Hcn Intermolecular Forces

No comments:. For example, paraffin wax (C 30 H 62) is a non-polar solute that will dissolve in non-polar solvents like oil, hexane (C 6 H 14) or carbon tetrachloride (CCl 4). It consists of atom-atom potentials for the representation of repulsion and dispersion energies and an evaluation of the electrostatic energy in terms of partitioned multipole moments of the monomer electron distributions. a) London dispersion c) hydrogen bonding b) dipole-dipole d) all of the above. dipole-dipole interactions hydrogen bonding dispersion forces. All solids also have a vapor pressure. Question 1. List the intermolecular forces present in each. 1) For each of the following compounds indicate which intermolecular force is most important: a) FCN dipole-dipole force. So, London Dispersion has an effect on all molecules, and these temporary dipoles are the temporary shift in electrons as they change their positions. This is the driving force of atoms to combine with other atoms in so called "chemical reactions. Dipole-Dipole: SF4 is a polar molecule. 35 difference in electronegativity for the H-C bond shows that it is essentially nonpolar. Intermolecular Forces Webquest. HCN dipole Investigate polar intermolecular interactions using HCN. Each dot represents one electron. Therefore, CH2Cl2 interacts with H2O via dipole-dipole forces, while CCl4 only interacts with water via dipole/induced dipole forces or LDFs, which would be weaker. This force is sometimes called an induced dipole-induced dipole attraction. Note: If you aren't happy about intermolecular attractions then you really ought to follow this link before you go on. Dipoles are stronger than London Forces alone, so polar molecules tend to have stronger intermolecular forces than nonpolar molecules of a similar size and polarity. 6 mL of aqueous 0. The ethane/ethyne molecule is nonpolar because all of the bond dipoles in the molecule. Dispersion: These two molecules are adjacent in a liquid, so they are attracted by dispersion. Lewis Dot Structure Worksheet. More Intermolecular Force Practice Problem Answers. Combining Eqs. assigning boiling points to a substance on the basis of intermolecular forces Submitted by VCU12 on Wed, 02/06/2008 - 16:38 I was wondering if anyone could explain to me the best way to figure out the boiling points of certain substances. When C4H10O interacts with C4H10O, there are two intermolecular forces that occur: Dipole-dipole: The positive H of C 4 H 10 O is attracted to the negative O of C 4 H 10 O. 50 M sodium hydroxide are mixed. 2 Intermolecular Forces • Intermolecular forces are much weaker than ionic or covalent bonds (e. Why does CH3I have stronger intermolecular forces than CH3Cl? Chemistry I figured that CH3Cl would have stronger IM forces because Cl is able to pull on the carbon's electrons more than I is because Cl is much smaller than I, which would cause a greater dipole moment in CH3Cl and stronger intermolecular forces. ; Intermolecular forces are weaker than intramolecular forces. Dipole-dipole: Occurs non-polar in molecules and is directly proportional to the number of electrons in the molecules. Intermolecular forces in van der waals dimers Intermolecular forces in van der waals dimers Hurst, G. It causes a temporary covalent bond between the hydrogen of one molecule and the nitrogen, oxygen, or flourine of another molecule. dinitrogen tetrachloride 14. For example, if you're looking at a water molecule,. The other molecular weights are H 2 (2), CO (28), HF (20), and Ne (20). Therefore, CH2Cl2 interacts with H2O via dipole-dipole forces, while CCl4 only interacts with water via dipole/induced dipole forces or LDFs, which would be weaker. More Intermolecular Force Practice Problem Answers 1) For each of the following compounds indicate which intermolecular force is most important: a) FCN dipole-dipole force b) HCN dipole-dipole force c) C 2 H 6 Van der Waals forces d) CF 2 H 2 dipole-dipole force. forces, but dipole-dipole forces are stronger. It therefore allows one to draw some conclusions about this interaction. What is the intermolecular force of HCN? (d) HCN is a linear molecule; it does have a permanent dipole moment ; it does contain N, however the nitrogen is not directly bonded to a hydrogen. London forces are the only intermolecular force that propane molecules experience. Propane: C3H8. A)each nitrogen has one nonbinding electron pair B)each hydrogen has one nonbonding electron pair C)each nitrogen has two nonbinding electron pairs. For example, paraffin wax (C 30 H 62) is a non-polar solute that will dissolve in non-polar solvents like oil, hexane (C 6 H 14) or carbon tetrachloride (CCl 4). Factors that affect the strength of London Forces 1) The more protons and electrons in a molecule, the stronger the London Forces-(higher molar mass usually means stronger London Forces) 2) A molecule with a linear shape will have stronger London Forces than a molecule with a spherical shape (if p+ and e-are the same). So these are forces between molecules or atoms or ions. The results for anisole and N-N dimethyl-aniline also fall on this line, but it should be noted that in these cases there may be. A)each nitrogen has one nonbinding electron pair B)each hydrogen has one nonbonding electron pair C)each nitrogen has two nonbinding electron pairs. Contact with the unconfined. ; Buckingham, A. With the exception of ionic compounds, the words polar and nonpolar only pertain to MOLECULAR substances and the difference between them dictates the strength and type of IMF. as an ideal gas system and ignore the intermolecular forces. The result of this dipole-dipole interaction though, is that molecules want stay as the liquid for as long as possible, because there are intermolecular forces holding them together. This is the dominant intermolecular force when an ionic compound dissolves in water. Just because HF exhibits hydrogen bonding, and hydrogen bonding is stronger than the three van der Waals forces, that doesn’t mean that HF exhibits only hydrogen bonding. Explore intermolecular forces by seeing how many drops of a liquid a penny can hold. CH3OH Based on the intermolecular forces reported for the compounds in problem 1, predict the order of increasing boiling point. What is the primary intermolecular force present in the following compounds? a. Intermolecular Forces In the image to the left, quartz is displayed with the polar molecule HCN and the non-polar CO2. All van der Waals forces are weak compared to ionic bonds, covalent bonds, and metallic bonds. dinitrogen tetrachloride 14. The result of this dipole-dipole interaction though, is that molecules want stay as the liquid for as long as possible, because there are intermolecular forces holding them together. London Dispersion Forces are attractive IMF's that occur when spontaneous dipoles are formed randomly or induced by other charged species in neutral polarizable molecules. Download this CHMA10H3 study guide to get exam ready in less time! Study guide uploaded on Dec 3, 2018. HCN C What is the primary intermolecular force present in the following compounds? a. Answer to: 15. In general, deviation. For the compound with the highest boiling point, does that mean the vapor pressure will be high or low? Why?. The intermolecular force is the sum of all the forces between two neighboring molecules. In this case, the -OH group has been replaced by a chlorine atom. HCN is covered under AX2, which is a linear molecular geometry. For example, paraffin wax (C 30 H 62) is a non-polar solute that will dissolve in non-polar solvents like oil, hexane (C 6 H 14) or carbon tetrachloride (CCl 4). tutor-homework. The present chapter deals with systems in which intermolecular interactions are ignored. And an intermolecular force would be the force that are between molecules. This is the driving force of atoms to combine with other atoms in so called "chemical reactions. State a generalisation relating London dispersion forces to the number of electrons in atoms or molecules. If the intermolecular forces are relatively weak, the boiling point will be relatively low. Dispersion forces are intermolecular forces which are relatively weak when compared with covalent or ionic bonds, so the melting points of the halogens are low. (d) HCN is a linear molecule; it does have a permanent dipole moment; it does contain N, however the nitrogen is not directly bonded to a hydrogen. An important type of dipole-dipole forces are hydrogen bonds. For example, the covalent bond, involving sharing electron. Any contribution is appreciated. The formula of glycerol is CHOH(CH2OH)2. Remember, the prefix inter means between. Insoluble in water and has a high thermal stability. dipole-dipole interactions hydrogen bonding dispersion forces b. Dispersion forces & dipole-dipole forces c. What is a temporary dipole? What types of molecules are capable of having temporary dipoles? What is the name of the intermolecular force that involves temporary dipoles? 9. The only intermolecular forces that occur between nonpolar molecules are dispersion forces. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Intermolecular Forces Between two molecules of acetic acid there are 3 forces of attraction that affect them. A dipole is a molecule that has split charge. Liquids boil when the molecules have enough thermal energy to overcome the intermolecular attractive forces that hold them together, thereby forming bubbles of vapor within the liquid. Therefore, it will experience London Dispersion Forces which are forces that exist among non-polar molecules. Hydrogen Peroxides AX form is an AX2E2, meaning that is bent with 109. The strongest intermolecular forces in each case are: "CHF"_3: dipole - dipole interaction "OF"_2: London dispersion forces "HF": hydrogen bonding "CF"_4: London dispersion forces Each of these molecules is made up of polar covalent bonds; however in order for the molecule itself to be polar, the polarities must not cancel one another out. There are three types of intermolecular forces. Properties: burns in air, reacts with halogens, concentrated sulfuric acid, nitrogen dioxide. The intermolecular forces are correct and are well explained. NH3 H2O SnCl2 CH2F2 5. Use this number to determine the electron pair geometry. Back to Molecular Geometries & Polarity Tutorial: Molecular Geometry & Polarity Tutorial. Similar Questions. ; Intermolecular forces are weaker than intramolecular forces. 3 -dispersion forces b. Arrange the following intermolecular attractions in order of increasing strength: dipole-dipole interactions, London dispersion forces, hydrogen bonds. The Journal of Chemical Physics 1997 , 107 (20) , 8327-8337. Van der Waals (a. That one will have the strongest IMF's overall. Intermolecular forces are weak attractive forces between molecules. The hydrogen bond is shown as a dotted line. 0 M hydrocyanic acid (HCN), a weak acid, and 100. Dipole-dipole forces have strengths that range from 5 kJ to 20 kJ per mole. Identify all type(s) of intermolecular force(s) between molecules of each substance using LF=London forces, DDF=Dipole-dipole forces, and HB=Hydrogen bonds. It is colorless gas above 78 degrees Fahrenheit. The relative significance of bulk dielectric effect and intermolecular interaction varies in different cases. The first type, which is the weakest type of intermolecular force, is a London Dispersion force. van der Waals forces – Keesom force, Debye force, and London dispersion force. With the exception of ionic compounds, the words polar and nonpolar only pertain to MOLECULAR substances and the difference between them dictates the strength and type of IMF. Although such induced moments vary in magnitude, in principle, an electric. This is the dominant intermolecular force when an ionic compound dissolves in water. If this molecule was bonded to itself the intermolecular forces that would be sent are: London Dispersion Forces: It has a temporaray dipole direct effect of eectron motion in molecule. hydrogen bonding and induced dipole/induced dipole force e. The increased kinetic energy with rising temperature overcomes the cohesive intermolecular forces of attraction. " (Wikipedia) Polar molecules. Covalent bonds form between non-metals. Title: Pressure Broadening of the HCN Band Lines and Intermolecular Forces: Authors: Herzberg, G. The strongest intermolecular forces in each case are: "CHF"_3: dipole - dipole interaction "OF"_2: London dispersion forces "HF": hydrogen bonding "CF"_4: London dispersion forces Each of these molecules is made up of polar covalent bonds; however in order for the molecule itself to be polar, the polarities must not cancel one another out. Intermolecular Forces, Liquids, and Solids 11. a)Hydrogen bonding is found in water, to a lesser volume in ammonia, and not in any respect in methane. A) of weaker intermolecular forces B) the molecules are more polarizable HCN E) CO 2. 1) gives the accumulated data from the literature , , , on the binding energies and the equilibrium distances of the primary (or chemical) and secondary (or intermolecular) forces. Smaller molecules (atoms) have smaller London forces. Hydrogen Bonding. is a particularly strong type of dipole-dipole force that occurs when hydrogen is attached to nitrogen, oxygen, or fluorine. And so that's different from an intramolecular force, which is the force within a molecule. CH3OH Based on the intermolecular forces reported for the compounds in problem 1, predict the order of increasing boiling point. A selection of dimers is studied, with emphasis on cases where the experimental structure is not reliably predicted by the hard‐sphere electrostatic model. Propane molecules are relatively small, so the London forces between them are weak -- too weak to hold them together in solid or liquid phase at room temperature. What intermolecular forces are present in each of the substances: CH3F; C6H5OH; HF; C2H6; C5H12 a. When sugar dissolves in water, the weak bonds between the individual sucrose molecules are broken, and these C 12 H 22 O 11 molecules are released into solution. Using the data from the Boiling Point Vs Number of electrons (Noble gases) table, plot a graph of boiling point versus number of electrons for the noble gases. With the exception of ionic compounds, the words polar and nonpolar only pertain to MOLECULAR substances and the difference between them dictates the strength and type of IMF. 2CH3CH2OH +HCO2H ⇀↽ HCO2CH2CH3. Instrumental techniques Phar 6521 1 2. Intermolecular Forces, Liquids, and Solids 11. Substances with stronger intermolecular attractions have. and a higher melting point. Microsoft Word - GCI_Mock_3. Chapter 11: Intermolecular Forces. Types of Intermolecular Forces. Co-ordinate covalent bond: a bond in which both of the electrons were contributed by one of the atoms 2. For example, if you're looking at a water molecule,. CHEMISTRY CONCEPT: The stronger the intermolecular forces between a substance, the higher the. In particular, long-range forces are shown to be the sum of the van der Waals force and hydrogen bonding. Intermolecular attractive forces, collectively referred to as van der Waals forces, are responsible for the behavior of liquids and solids and are electrostatic in nature. low- because of weak intermolecular forces. Just because HF exhibits hydrogen bonding, and hydrogen bonding is stronger than the three van der Waals forces, that doesn’t mean that HF exhibits only hydrogen bonding. Types of intermolecular forces: dipole-dipole, London dispersion, hydrogen bond FORMULA LEWIS STRUCTURE MOLECULAR SHAPE POLAR or NONPOLAR TYPE OF INTERMOLECULAR FORCE BETWEEN 2 OR MORE OF THESE MOLECULES ex CH 3Cl tetrahedral polar dipole-dipole 1) CI 4 2) HF 3) NF 3 4) CO 2 5) HCN 6) H2O 7) C3H8. The electron cloud in I 2 is, therefore, much more polarisable leading to stronger dispersion forces in I2. The attraction is caused by the exchange of electrons between molecules. Contact with the unconfined. Read and learn for free about the following article: Intramolecular and intermolecular forces If you're seeing this message, it means we're having trouble loading external resources on our website. The Organic Chemistry Tutor 624,733 views 45:36. • Melting point linked to strength of forces between particles for BOTH solids. Introduction. Start studying Intermolecular Forces Mastering Chemistry. These interactions influence the properties of the compounds like boiling point, melting point and so on. 1986-05-01 00:00:00 For several van der Waals molecules, the results of ab initio intermolecular perturbation theory are compared with the simple Buckingham‐Fowler model. Substances with stronger intermolecular forces take longer to evaporate than substances with weaker intermolecular forces. They differ in their strength and include the following. molecules will have enough energy to overcome the intermolecular forces and enter into the gas phase. The Lewis Dot Structure for CH4 is shown above. Intermolecular forces are weak relative to intramolecular forces - the forces which hold a molecule together. The only intermolecular forces between NH4+ ions are van der waals (london dispersion forces). - Part A What intermolecular forces are present in each of the substances? Drag each item to the appropriate bin. AP Chemistry study material. The intermolecular forces of the remaining substances depend on molecular weight, polarity, and hydrogen bonding. For several van der Waals molecules, the results of ab initio intermolecular perturbation theory are compared with the simple Buckingham‐Fowler model. Therefore dispersion forces and dipole-dipole forces act between pairs of HCN molecules. Dipole-Dipoles are permanent charge seperations. Examples of intermolecular forces include the London dispersion force, dipole-dipole interaction, ion-dipole interaction, and van der Waals forces. Intermolecular forces are forces of attraction or repulsion which act between neighboring particles (atoms, molecules or ions). Dipole-dipole attractions result from the electrostatic attraction of the partial negative end of one dipolar molecule for the partial positive end of another. Chemistry Group Work: Intermolecular Forces For questions 1-5: a) Draw the 3-D Lewis structures, showing any polar bonds with + and - symbols in the appropriate location. The polar bonds in "OF"_2, for example, act in. Intermolecular forces in aggregates of asphaltenes and resins Article in Petroleum Science and Technology 09-10 10(9-10):983-997 · January 2002 with 123 Reads How we measure 'reads'. Mostly gases and liquidsat room temp. HCN C What is the primary intermolecular force present in the following compounds? a. A dipole is a molecule that has split charge. 5--Ion forces -dipole forces -dispersion forces e. The increase in melting point down the group is due to the increase in intermolecular dispersion forces experienced as a result of the increased number of electrons. They come in many forms, giving us insight into how molecules interact with each other as well as what chemical properties a substance may have. Intermolecular Forces? Three of the fundamental types of intermolecular forces are dispersion forces (or London forces), dipole-dipole forces, and hydrogen bonding. ↑ ΔEN α ↑ intermolecular force (dipole - dipole force) Explain why Chlorine (Cl2) is a gas, bromine (Br2) is a liquid, and iodine (I2) is a solid. London dispersion forces and dipole-dipole forces are collectively known as van der Waals forces. Intermolecular forces are weak attractive forces between molecules. Hydrogen bonds are much weaker than covalent bonds, only about 5 to 10% as strong, but are generally much stronger than other dipole-dipole attractions and dispersion forces. , 16 kJ/mol versus 431 kJ/mol for HCl). NH3 H2O SnCl2 CH2F2 5. The forces result from the actions of the kinetic energy of atoms and the slight positive and negative electrical charges on different parts of a molecule that affect its neighbors and any solute that may be present. negative ions held together by electrostatic forces (B) closely packed lattice with delocalized electrons throughout (C) strong single covalent bonds with weak intermolecular forces (D) strong multiple covalent bonds with weak intermolecular forces (E) macromolecules held together with strong polar bonds 19. Paraffin wax will NOT dissolve in polar solvents such as water (H 2 O) or ethanol (ethyl alcohol, C 2 H 5. Any contribution is appreciated. You try: determine the Intermolecular forces (IMFs) present for all of the molecules on worksheet pg5. Intermolecular Forces - Hydrogen Bonding, Dipole-Dipole, Ion-Dipole, London Dispersion Interactions - Duration: 45:36. Unlike forces between molecules with permanent dipole moments, dispersion forces always act to attract the molecules to each other regardless of the relative orientation of the. Dipole-dipole: _ attractive forces between polar molecules (pure substance or mixture) ___. C3h4 Iupac Name. Therefore, it will experience London Dispersion Forces which are forces that exist among non-polar molecules. Properties of Solids and Liquids Worksheet Objectives: • Identify the information given in a heating or cooling curve. Dispersion forces are found in all substances. If you're behind a web filter, please make sure that the domains *. Attractive intermolecular forces are categorized into the following types: Hydrogen bonding. Give an example of each and describe what characteristic that example has that results in each type of intermolecular force. Name _____ Honors Chemistry ___/___/___ Covalent Compounds & Intermolecular Forces A covalent compound is a compound in which the outer energy level (valence) electrons are shared by two or more atoms. The result of this dipole-dipole interaction though, is that molecules want stay as the liquid for as long as possible, because there are intermolecular forces holding them together. WEEK 22 AGENDA: Unit 5 (Covalent Compounds) course website: kachemistry. The other molecular weights are H 2 (2), CO (28), HF (20), and Ne (20). For example $\ce{HCN}$ has a $\mathrm pK_\mathrm a$ value of 9. Covalent bonds can consists of one pair of shared electrons (a single bond), two. Both Br 2 and F 2 consist of 2 equally electronegative molecules, so Van der Waals' (VdW) forces are the intermolecular forces present. Hydrogen cyanide (HCN) and isocyanide (HNC) are among the most abundant organic. And Hydrogen bonding is a special case of dipole-dipole bonding that only appears in HF, HN and HO molecules due to the large difference in electronegativities. In fact, all molecules exhibit London dispersion forces. Covalent bonds form between non-metals. Thus, intramolecular forces are much stronger than intermolecular forces. Intermolecular Forces. ammonia 12. dinitrogen tetrachloride 14. higher than the normal boiling point of CF 4 (l) (145 K)? A) The C-Cl bonds in CCl 4. This forms a dipole (dipole means two oppositely charged ends). Since the ammonia ion has hydrogen atoms bonded to nitrogen, a very electronegative atom, the molecule is also polar since the nitrogen atom more strongly pulls on the electrons from the hydrogen atoms than the hydrogens themselves do. What is the strongest intermolecular force present for each of the following compounds? 1) water _____ 2) carbon tetrachloride _____. Intermolecular forces in aggregates of asphaltenes and resins Article in Petroleum Science and Technology 09-10 10(9-10):983-997 · January 2002 with 123 Reads How we measure 'reads'. Be very specific! Intermolecular force (IMF) is responsible for the different states of the halogens. Determine the intermolecular forces present in NH2Cl. Draw the electron dot structures for each molecule. Asked in Chemistry , Chemical Bonding What intermolecular forces are present in HCN ?. They are weak compared. Question 1. These forces are responsible for the formation of chemical bonds. Since dipole-dipole forces are stronger than dispersion, I can say that H 2 S has a higher boiling point, yes? Thank you for your time and help!. The substance is at its normal melting point at time (A) T1 (B) T2 (C) T3 (D) T4 (E) T5 2. iii: Draw a diagram showing the resulting hydrogen bonds between water and the compound chosen in. In fact, all molecules exhibit London dispersion forces. Lewis Dot Structure Worksheet. Answer is: ammonia experience only dispersion intermolecular forces with BF 3 (boron trifluoride) because BF 3 is only nonpolar molecule (vectors of dipole moments cansel each other, dipole moment is zero). London dispersion forces are considered as the weakest intermolecular force between adjacent molecules or atoms. " (Wikipedia) Polar molecules. Download this CHMA10H3 study guide to get exam ready in less time! Study guide uploaded on Dec 3, 2018. A) of weaker intermolecular forces B) the molecules are more polarizable HCN E) CO 2. The London dispersion force (intermolecular force) is a temporary attractive force between molecules. intermolecular forces. Dispersion: These two molecules are adjacent in a liquid, so they are attracted by dispersion. Using the data from the Boiling Point Vs Number of electrons (Noble gases) table, plot a graph of boiling point versus number of electrons for the noble gases. Propane molecules are relatively small, so the London forces between them are weak -- too weak to hold them together in solid or liquid phase at room temperature. Oxidation-Reduction (Redox) The items exchanged are electrons. For the compound with the highest boiling point, does that mean the vapor pressure will be high or low? Why?. The Lewis structure and geometric sketch for HCN are the same: The electronegativities of hydrogen, carbon, and nitrogen are 2. Since the ammonia ion has hydrogen atoms bonded to nitrogen, a very electronegative atom, the molecule is also polar since the nitrogen atom more strongly pulls on the electrons from the hydrogen atoms than the hydrogens themselves do. Intermolecular Forces 3) Dipole-Dipole Forces Forces b/w polar molecules (H 2S, HCl…) (+) end of one molecule is attracted to (–) end of another. We know that while carbon dioxide is a non-polar molecule, we can still freeze it (and we can also freeze all other non-polar substances). This type of bond is not as strong as some of the other type of bonds and can be easily broken. Intermolecular forces are forces of attraction or repulsion which act between neighboring particles (atoms, molecules or ions). Introduction to Organic Chemistry. Journal of Chemical Physics, 106 , 6288. SeF4 or SeF6. What is the strongest intermolecular force present for each of the following molecules? 1) hydrogen (H 2) London dispersion forces 2) carbon monoxide (CO) London dispersion forces 3) silicon tetrafluoride (SiF 4) London dispersion forces 4) nitrogen tribromide (NBr 3) dipole-dipole forces 5) water (H 2 O) hydrogen bonding 6) acetone (CH 2. They are hydrogen-bonding interactions, the dipole-dipole interactions and the induced dipole interactions. Ice, H2O, has a solid structure with alternating H-O interactions b. HCN C What is the primary intermolecular force present in the following compounds? a. Ion–induced dipole forces. H2 HBr HCN HFhydrogen bonding, dipole dipole, dispersion onlydipole dipole and dispersion onlydispersion only. Other Chemicals: Take a look at some other chemicals. 1 5 (I956, I957). a)Hydrogen bonding is found in water, to a lesser volume in ammonia, and not in any respect in methane. CH 2 Cl 2 Dipole-dipole forces The strongest intermolecular force in a polar molecule that cannot form hydrogen bonds is the dipole-dipole force e. Dipoles are stronger than London Forces alone, so polar molecules tend to have stronger intermolecular forces than nonpolar molecules of a similar size and polarity. Use this number to determine the electron pair geometry. The intermolecular forces increase with increasing polarization (i. What is the primary intermolecular force present in the following compounds? a. 8 amu) than in F2 (38. You will measure the mass of a sample that evaporates after 3 minutes, then take the difference between that mass and the initial mass of the sample to determine the percent by mass of the sample that evaporated. The electron cloud in I 2 is, therefore, much more polarisable leading to stronger dispersion forces in I2. Answer to: 15. So these are forces between molecules or atoms or ions. Candidates should be able to: (a) describe hydrogen bonding and van der Waals forces (permanent, temporary and induced dipole); (b) deduce the effect of van der Waals forces between molecules on the physical properties of substances;. Intermolecular Forces. Lewis Dot Structure Worksheet. However, N 2 is a gas at room conditions because the intermolecular forces between different N 2 molecules are very weak. There are three types of interactions through which the molecules are stabilized. What type of intermolecular forces do the following compounds contain? a. Two quantum mechanical approximation formulas due to Slater and Kirkwood are modified empirically such as to relate the empirical intermolecular force constants of a two‐parameter potential to the average polarizabilities and the number of valence electrons of the interacting molecules. The geometry of the SO 3 molecule is best described as (A) trigonal planar (B) trigonal pyramidal (C) square pyramidal (D) bent (E) tetrahedral _____ 2. /4 – t (• 2. Liquids boil when the molecules have enough thermal energy to overcome the intermolecular attractive forces that hold them together, thereby forming bubbles of vapor within the liquid. What is a temporary dipole? What types of molecules are capable of having temporary dipoles? What is the name of the intermolecular force that involves temporary dipoles? 9. 4a: Identify the intermolecular forces present in hydrogen iodide in the liquid state, HI(l). The Lewis structure and geometric sketch for HCN are the same: The electronegativities of hydrogen, carbon, and nitrogen are 2. Similarly, solids melt when the molecules. When C 3H 8 is bonded the force that holds it together is London dispersion. If yes, then this type of intermolecular forces would resemble (but not identical, by definition, to) the permanent dipole-dipole forces in water. Insoluble in water and has a high thermal stability. These are H 2 O–HCN intermolecular distance, r (H 3 O 4 ), which decreases by nearly 0. Orient data files for HCN and methyl fluoride. 4 -dispersion forces. b) Identify all of the intermolecular forces in each compound: (dispersion force, dipole interaction or hydrogen bonding) 1) carbon disulfide 2) ammonia 3) oxygen 4) CH2F2 5) C2H6. intermolecular forces act between the molecules. Using the data from the Boiling Point Vs Number of electrons (Noble gases) table, plot a graph of boiling point versus number of electrons for the noble gases. e) Vapor Pressure As the intermolecular forces increase (↑), the vapor pressure decreases (↓). NCl 3-LD, VDW forces. Intermolecular interaction potentials of methane and ethylene dimers calculated with the Møller–Plesset, coupled cluster and density functional methods. Intermolecular Forces, Liquids, and Solids 11. Inside a calorimeter, 100. And so let's look at the first. Google Scholar. This means that it contains no permanently dipolar molecules; lacking a dipole. negative ions held together by electrostatic forces (B) closely packed lattice with delocalized electrons throughout (C) strong single covalent bonds with weak intermolecular forces (D) strong multiple covalent bonds with weak intermolecular forces (E) macromolecules held together with strong polar bonds 19. London Dispersion Forces) and Dipole-Dipole interactions. London dispersion ONLY occurs in nonpolar molecules. The action of intermolecular forces must be observed through a microscope and by analyzing data, including vapor pressure. There are three types of interactions through which the molecules are stabilized. assigning boiling points to a substance on the basis of intermolecular forces Submitted by VCU12 on Wed, 02/06/2008 - 16:38 I was wondering if anyone could explain to me the best way to figure out the boiling points of certain substances. Back to Molecular Geometries & Polarity Tutorial: Molecular Geometry & Polarity Tutorial. and a higher melting point. Answer is: ammonia experience only dispersion intermolecular forces with BF₃ (boron trifluoride) because BF₃ is only nonpolar molecule (vectors of dipole moments cansel each other, dipole moment is zero). HCN does not hydrogen bond to itself. Intermolecular vs Intramolecular • 41 kJ to vaporize 1 mole of water (inter) • 930 kJ to break all O-H bonds in 1 mole of water (intra) Generally, intermolecular forces are much weaker. It is formed from both natural processes and human activities. Answer to: 15. Which of the following substances has London dispersion forces as its only intermolecular force? a. The interparticle force is the same as the intermolecular force: the ionic bond and it is the strongest of the interparticle forces. Water is an example of a substance in which hydrogen bonding occurs. ii: State and explain which compound can form hydrogen bonds with water. Hydrogen can never be at the center. carbon tetrafluoride 13. And an intermolecular force would be the force that are between molecules. Ion-dipole forces attract the positive (hydrogen) end of the polar water molecules to the negative chloride ions at the surface of the solid, and they attract the negative (oxygen) ends to the positive potassium ions. I hope the article helped you to understand the organic compounds in a better manner. Intermolecular Forces In the image to the left, quartz is displayed with the polar molecule HCN and the non-polar CO2. Intramolecular forces is the force of attraction between atoms in a molecule. This is called dipole -dipole interaction. Ionic - result of electrostatic forces between ions Coulomb's law: examples: NaCl(s), solid sodiumnitrate, NaOAc(s) Ion-dipole - interaction of an ion (cation or anion) with a polar molecule examples: dissolving any ionic compound in water Dipole-dipole - Interaction of polar molecules with other polar molecules examples: acetone in acetone, triethyl amine in acetone. Ion–dipole forces. Properties of Solids and Liquids Worksheet Objectives: • Identify the information given in a heating or cooling curve. kJ of heat energy is absorbed at its melting temperature of 5. As the melting point is reached there will be a rearrangement of HCN molecules. The Organic Chemistry Tutor 994,425 views. Intermolecular forces are not strong enough to prevent the sample from being a fluid (Solid (s), Liquid (l), Gas (g)) l and g Particles within the sample are highly organized, held together in a relatively rigid structure (Solid (s), Liquid (l), Gas (g)). Benzene is a great chemical. b) Identify all of the intermolecular forces in each compound: (dispersion force, dipole interaction or hydrogen bonding) 1) carbon disulfide 2) ammonia 3) oxygen 4) CH2F2 5) C2H6. O has a smaller atomic radius than N, as O has a more positive nucleus, but the valance electrons in both N and O are in the same. The dash model for N2H4 with the one line of symmetry, shown in red. Be very specific! Intermolecular force (IMF) is responsible for the different states of the halogens. MSJChem - Topic 4 - Intermolecular forces Answers: 1) London dispersion forces < Dipole-dipole forces < Hydrogen bonding 2) Non-polar molecules have London dispersion forces, polar molecules have dipole-dipole forces and molecules with H-O, H-N or H-F have hydrogen bonding as the strongest intermolecular force between molecules. This is the rapid changing of bonds between the hydrogen and the oxygen, and where they actually began. We have changed simple atomic orbitals to atomic orbitals suitable for bonding. Dispersion forces only b. Draw each Lewis structure. 9b Addition of HCN. The theoretical calculation and experimental determination of intermolecular forces has been a fundamental subject discussed intensively on many review articles and books for many years. Table 1-5 (see 1. The last force of attraction is hydrogen bonding. ; Spinks, J. The species that gains electrons is said to be reduced (and is called the oxidizing agent). Created by MakeTheBrainHappy. Ethylene glycol is widely used to inhibit the formation of natural gas clathrates (hydrates) in long multiphase pipelines that convey natural gas from remote gas fields to a gas processing facility. … List all the intermolecular forces present in pure acetone. In other words, the cause of these intermolecular forces is not an induced temporary dipole in neighboring molecules. The formula of glycerol is CHOH(CH2OH)2. Here are some tips and tricks for identifying intermolecular forces. The only intermolecular forces that occur between nonpolar molecules are dispersion forces. Thus, intramolecular forces are much stronger than intermolecular forces. A certain gaseous oxide of sulfur has an effusion rate that is … will exhibit the strongest dipole-dipole intermolecular force with … CH2Cl2) 20. 9b Addition of HCN. The dominant intermolecular forces in octane are (A) dipole-dipole forces (B) London dispersion forces (C) hydrogen bonding (D) covalent bonding 15. With the exception of ionic compounds, the words polar and nonpolar only pertain to MOLECULAR substances and the difference between them dictates the strength and type of IMF. 1986-05-01 00:00:00 For several van der Waals molecules, the results of ab initio intermolecular perturbation theory are compared with the simple Buckingham‐Fowler model. What is the primary intermolecular force present in the following compounds? a. Is Co2 Ionic Or Covalent. kJ of heat energy is absorbed at its melting temperature of 5. That one will have the strongest IMF's overall. The motion of electrons around the atom temporarily charges the molecule. Remember, the prefix inter means between. Ion–induced dipole forces. Intermolecular Forces Proceedings of the Fourteenth Jerusalem Symposium on Quantum Chemistry and Biochemistry Held in Jerusalem, Israel, April 13-16, 1981. I hope the article helped you to understand the organic compounds in a better manner. The intermolecular forces between $\ce{CO2}$ molecules are dispersion forces, while the forces between $\ce{CO}$ molecules are mostly dipole-dipole attraction forces. What kind(s) of intermolecular forces exist in ch2cl2(l)? select all that apply. Chad breaks down the Nucleophilic Addition of HCN to Ketones and Aldehydes to produce Cyanohydrins. relative strength of intermolecular forces (so) bromine has stronger (London) forces (between molecules) / more (heat) energy is needed to overcome the London forces between bromine molecules / greater temporary dipole – induced dipole forces (1) Allow reverse arguments Allow correct formulae Bromine has 35/70 electrons and chlorine has. If two XeF4 molecules were to bond together, the only intermolecular force that would occur would be the London Dispersion Force. The rotational spectrum, geometry, and intermolecular force constant of the heterodimer of hydrogen cyanide and fluoroform Article (PDF Available) in The Journal of Chemical Physics 84(4):1988. • Melting point explained with reference to particles,. The strongest intermolecular force in a polar molecule is the dipole-dipole force d. The three types of intermolecular forces are: Dipole-dipole interactions London dispersion forces Hydrogen bonds The dipole forces are attractive. Difluoromethane is a member of fluoromethanes. Ice, H2O, has a solid structure with alternating H-O interactions b. This is the driving force of atoms to combine with other atoms in so called "chemical reactions. “The compressibility factor (Z), also known as the compression factor or the gas deviation factor, is the ratio of the molar volume of a gas to the molar volume of an ideal gas at the same temperature and pressure. So these are intermolecular forces that you have here. Lastly, it has hydrogen bonding, which is a special case of dipole-dipole. The types of intermolecular forces present in ammonia, or NH3, are hydrogen bonds. The Journal of Chemical Physics 1997 , 107 (20) , 8327-8337. dipole-dipole forces forces only in polar substances, strength of force increases with molar mass: hydrogen bonds very strong dipole force, only exists in compounds with H directly attached to N, O, or F: ion-dipole forces forces between an ion and a polar molecule. Properties of Solids and Liquids Worksheet Objectives: • Identify the information given in a heating or cooling curve. It is also used in cleaning fluids and as a starting material to make other chemicals. Based on electrostatic interaction, three kinds of intermolecular forces. Using your knowledge of intermolecular forces, why wouldn’t it be better to use a compound like glycerol. Chromatography is a physical method of separation in which the components to be separated are distributed between two phases (KD/P = Distribution/partition constant) one of which is stationary (stationary phase) while the other (the mobile phase) moves through it in a definite direction. And Hydrogen bonding is a special case of dipole-dipole bonding that only appears in HF, HN and HO molecules due to the large difference in electronegativities. Using your knowledge of intermolecular forces, why wouldn't it be better to use a compound like glycerol. ; Fowler, P. Chapter 11: Intermolecular Forces. document PDF (Teacher's Edition Only) Test your knowlege of IMFs. Intermolecular Forces Practice pg 247 #1-8, 11-14 1. The three bond dipole moments are then 120° apart and of equal magnitude all directed at the more electronegative hydrogen atoms. Molecules can have any mix of these three kinds of intermolecular forces, but all substances at least have London dispersion forces. With the exception of ionic compounds, the words polar and nonpolar only pertain to MOLECULAR substances and the difference between them dictates the strength and type of IMF. Comparing Intermolecular Forces We can identify the intermolecular forces operative in a substance by considering its composition and structure. Using your knowledge of intermolecular forces, why wouldn't it be better to use a compound like glycerol. in terms of the intermolecular forces between each of the solutes and water. Properties of Solids and Liquids Worksheet Objectives: • Identify the information given in a heating or cooling curve. London dispersion and hydrogen bonds. London Dispersion Forces - the force of attraction between all molecules (any two at one time), created by temporary dipoles, which are caused by the movement of electrons around two atoms. Nitriles therefore have strong permanent dipole-dipole attractions as well as van der Waals dispersion forces between their molecules. Dipole-dipole: Occurs non-polar in molecules and is directly proportional to the number of electrons in the molecules. This is the dominant intermolecular force when an ionic compound dissolves in water. Hydrogen bond are stronger than Van der Waals forces therefore both NH3 and H2O will have higher boiling points than CH4. If two XeF4 molecules were to bond together, the only intermolecular force that would occur would be the London Dispersion Force. 8 amu) than in F2 (38. It is stronge than dispersion forces. They are hydrogen-bonding interactions, the dipole-dipole interactions and the induced dipole interactions. ; Intermolecular forces are weaker than intramolecular forces. AP Chemistry Chapter 11. The validity of the hard-sphere model in hydrogen bonded intermolecular interactions of HCN–HF. Table 1-5 (see 1. Dispersion forces & dipole-dipole forces & hydrogen bonding 2. Intermolecular Forces - Hydrogen Bonding, Dipole-Dipole, Ion-Dipole, London Dispersion Interactions - Duration: 45:36. Inside a calorimeter, 100. This type of bond is not as strong as some of the other type of bonds and can be easily broken. CH2Cl2 is polar, whereas CCl4 is not. b) HCN dipole-dipole force. asked by Jake on May 1, 2010. Introduction to Organic Chemistry. Intermolecular forces, like all interactions in chemistry, are electrostatic. For homework help in math, chemistry, and physics: www. As a result, CH2Cl2 has a greater solubility. 4a: Identify the intermolecular forces present in hydrogen iodide in the liquid state, HI(l). The forces result from the actions of the kinetic energy of atoms and the slight positive and negative electrical charges on different parts of a molecule that affect its neighbors and any solute that may be present. Identify if a Lewis Structure, the molecular shape, or both would show the following: 3. They are considerably weaker than a covalent or ionic bond. Dipole-Dipoles are permanent charge seperations. The strength of these attractive forces increases with increasing molecular weight and depends on molec-ular shapes. what type of intermolecular force describes the interaction between Ca2+ and Mg2. Intermolecular Forces Proceedings of the Fourteenth Jerusalem Symposium on Quantum Chemistry and Biochemistry Held in Jerusalem, Israel, April 13-16, 1981. Ion–dipole forces. HCN dipole Investigate polar intermolecular interactions using HCN. b) HCN dipole-dipole force. CH3CH2CH2CH2OH a) dipole-dipole forces b) London dispersion forces c) hydrogen bonding 2. Water has strong intermolecular forces (hydrogen bonds) while carbon tetrachloride only has weaker induced dipole forces. The strength of the four main intermolecular forces (and therefore their impact on boiling points) is ionic > hydrogen bonding > dipole dipole > dispersion Boiling point increases with molecular weight, and with surface area. Intermolecular forces are forces between molecules. Although this compound could be named as nitrogen monoxide monochloride, it is commonly known as Nitrosyl Chloride. Understand how intermolecular forces are related to states of matter. org are unblocked. Intermolecular Forces 11. 4 -dispersion forces. These relatively weak attractive forces are called intermolecular forces. The theoretical calculation and experimental determination of intermolecular forces has been a fundamental subject discussed intensively on many review articles and books for many years. There are different kinds of intermolecular forces(IMF) in covalent compounds. Hydrogen bonding is the main effectual intermolecular rigidity interior of NH2CH3 as not basically does it hydrogen bond interior of it self yet additionally helps Nitrogen to have a lone pair with helps with London-Dispersion Forces. , the fraction of members of the. Weaker Intermolecular Forces Ion-Dipole Forces An ion-dipole force is an attractive force that results from the electrostatic attraction between an ion and a neutral molecule that has a dipole. Substances with stronger intermolecular attractions have. Any contribution is appreciated. 6 mL of aqueous 0. The most common intermolecular forces (excluding hydrogen bonding--well, actually, "sort of" including it as we shall discuss below) are shown in the following figure from the text book. Two quantum mechanical approximation formulas due to Slater and Kirkwood are modified empirically such as to relate the empirical intermolecular force constants of a two‐parameter potential to the average polarizabilities and the number of valence electrons of the interacting molecules. Predict the intermolecular forces that would predominate in the following molecules: Argon CO2 HI HF. That one will have the strongest IMF's overall. State the intermolecular forces in each of the following groups of molecules and then number them from highest to lowest boiling points. Determine the intermolecular forces present in NH2Cl. Always consider the concept of vectors before going further to find. This is the dominant intermolecular force when an ionic compound dissolves in water. R DForm Approved REPORT DOCUMENTATION PAGE 0MB No. In drawing Lewis structures, a single line (single bond) between two elements represents: a shared pair of electrons. The Lewis structure and geometric sketch for HCN are the same: The electronegativities of hydrogen, carbon, and nitrogen are 2. Give an example of each and describe what characteristic that example has that results in each type of intermolecular force. Intermolecular forces act between molecules. Dipoles may form associations with other dipoles, induced dipoles or ions. Intermolecular forces (IMFs) are one of two kinds of forces that take place in and around a molecule. HCN - HYDROGEN CYANIDE. The origin of intermolecular forces varies depending on the structure and functional groups of the molecules involved. Combining Eqs. Candidates should be able to: (a) describe hydrogen bonding and van der Waals forces (permanent, temporary and induced dipole); (b) deduce the effect of van der Waals forces between molecules on the physical properties of substances;. This is called dipole -dipole interaction. If the intermolecular forces are relatively strong, the boiling point will be relatively high. The Journal of Chemical Physics 1997 , 107 (20) , 8327-8337. When C4H10O interacts with C4H10O, there are two intermolecular forces that occur: Dipole-dipole: The positive H of C 4 H 10 O is attracted to the negative O of C 4 H 10 O. There will also, of course, be dispersion forces and dipole-dipole attractions between the nitrile and water molecules. No comments:. The increase in melting point down the group is due to the increase in intermolecular dispersion forces experienced as a result of the increased number of electrons. They differ in their strength and include the following. Hydrogen cyanide (HCN) and isocyanide (HNC) are among the most abundant organic. Answer is: ammonia experience only dispersion intermolecular forces with BF₃ (boron trifluoride) because BF₃ is only nonpolar molecule (vectors of dipole moments cansel each other, dipole moment is zero). Intermolecular Forces One of the biggest sources of difficulty for a chemistry student is the distinction between chemical bonds and intermolecular forces. In contrast, intramolecular forces act within molecules. Check the orientation of the molecules, check energy of interaction. These kinds of structures can also be shown by representing each of the bonds with two dots. This type of bond is not as strong as some of the other type of bonds and can be easily broken. More Intermolecular Force Practice Problem Answers 1) For each of the following compounds indicate which intermolecular force is most important: a) FCN dipole-dipole force b) HCN dipole-dipole force c) C 2 H 6 Van der Waals forces d) CF 2 H 2 dipole-dipole force. One atom of the pair (the donor), generally a fluorine, nitrogen, or. an unshared pair of electrons. Chromatography is a physical method of separation in which the components to be separated are distributed between two phases (KD/P = Distribution/partition constant) one of which is stationary (stationary phase) while the other (the mobile phase) moves through it in a definite direction. Covalent bonds form between non-metals. London dispersion or Van der Waals forces. Ion–induced dipole forces. CHEMISTRY CONCEPT: The stronger the intermolecular forces between a substance, the higher the. Since the H-F bonds in the gaseous molecule are polar, hydrogen fluoride als. Learn vocabulary, terms, and more with flashcards, games, and other study tools. HCN bond angles of 180 degrees. Answer is: ammonia experience only dispersion intermolecular forces with BF 3 (boron trifluoride) because BF 3 is only nonpolar molecule (vectors of dipole moments cansel each other, dipole moment is zero). b) Identify all of the intermolecular forces in each compound: (dispersion force, dipole interaction or hydrogen bonding) 1) carbon disulfide 2) ammonia 3) oxygen 4) CH2F2 5) C2H6. kJ of heat energy is absorbed at its melting temperature of 5. 3 -dispersion forces b. Name the kind or kinds of intermolecular forces that must be overcome to convert the following from liquid or solid to gas: (a) Br2, (c) CH3OH, (d) CO2, (e) HCN, (f) NH3 (a) Br2 - London dispersion. 3 -dispersion forces b. And an intermolecular force would be the force that are between molecules. (e) Identify a compound from the table above that is nonpolar. Dispersion forces only b. It is the attraction between a positive element and a negative element from another molecule. in terms of the intermolecular forces between each of the solutes and water. In this case, the major effect comes from London forces. Therefore, CH2Cl2 interacts with H2O via dipole-dipole forces, while CCl4 only interacts with water via dipole/induced dipole forces or LDFs, which would be weaker. When electrons are. When C4H10O interacts with C4H10O, there are two intermolecular forces that occur: Dipole-dipole: The positive H of C 4 H 10 O is attracted to the negative O of C 4 H 10 O. Stone, Yuthana Tantirungrotechai and A. The three types of intermolecular forces are: Dipole-dipole interactions London dispersion forces Hydrogen bonds The dipole forces are attractive. These intermolecular forces are also sometimes called “London forces” or “momentary dipole” forces or “dispersion” forces. It is possible to draw the structure with two electrons in place of the lines to represent the covalent bonds, which would result in there being six shared electrons between the carbon and nitrogen. List and describe the three types of intermolecular forces: — — vx. HCN at 10380 A. There are three types of interactions through which the molecules are stabilized. London Dispersion Forces are attractive IMF's that occur when spontaneous dipoles are formed randomly or induced by other charged species in neutral polarizable molecules. OK, let's review the kinds of intermolecular forces you can have: 1. In general like dissolves like: Non-polar solutes dissolve in non-polar solvents. So, London Dispersion has an effect on all molecules, and these temporary dipoles are the temporary shift in electrons as they change their positions. The Organic Chemistry Tutor 994,425 views. Note that the hydrogen bond is linear with a bond angle of 180 o. While the RMA should be useless for very floppy monomer (e. The intermolecular forces of the remaining substances depend on molecular weight, polarity, and hydrogen bonding. The polar bonds in "OF"_2, for example, act in. 9b Addition of HCN. London dispersion or Van der Waals forces. ; Buckingham, A. Types of Intermolecular Forces. A dipole-dipole is an intermolecular force that occurs between two polar molecules. Which is a brittle, high-melting solid but dissolves in water? a. A dipole is a molecule that has split charge. Water is polar, and the dipole bond it forms is a hydrogen bond based on the two hydrogen atoms in the molecule. Liquids, Solids, and Intermolecular Forces Problem Set Phase Diagrams and Triple Point Diagrams Questions 1-2: Refer to the diagram below. Dispersion forces & dipole-dipole forces & hydrogen bonding 2. b) Identify all of the intermolecular forces in each compound: (dispersion force, dipole interaction or hydrogen bonding) 1) carbon disulfide 2) ammonia 3) oxygen 4) CH2F2 5) C2H6. The formula of glycerol is CHOH(CH2OH)2. HCN - HYDROGEN CYANIDE. SO 2 Dipole-dipole forces SO 2 is a bent, polar molecule. Dispersion forces only b. Forces that hold atoms in a molecule are called intramolecular forces. Ionic - result of electrostatic forces between ions Coulomb's law: examples: NaCl(s), solid sodiumnitrate, NaOAc(s) Ion-dipole - interaction of an ion (cation or anion) with a polar molecule examples: dissolving any ionic compound in water Dipole-dipole - Interaction of polar molecules with other polar molecules examples: acetone in acetone, triethyl amine in acetone. /intermolecular forces (in ethan al) OR hydrogen bonds are the strongest/strong intermolecular forces (1) Third mark: ethanoic acid has more electrons/ethanoic acid has the most electrons OR ethanoic acid is dimeric OR ethanoic acid forms dimers OR description of ethanoic acid dimers (N. The Journal of Chemical Physics 1997 , 107 (20) , 8327-8337. an octet of electrons. The last force of attraction is hydrogen bonding. The stronger the intermolecular forces (forces between molecules/atoms/ions), the higher the boiling point, or the more difficult it is to overcome those forces holding the molecule together. Intermolecular forces. atoms or ions. If this molecule was bonded to itself the intermolecular forces that would be sent are: London Dispersion Forces: It has a temporaray dipole direct effect of eectron motion in molecule. Select the interactions that can be explained by hydrogen bonding: a. Intermolecular forces, like all interactions in chemistry, are electrostatic. In this case, the -OH group has been replaced by a chlorine atom. Intermolecular Forces 2012. /4 - t (• 2.