122ch11a_001 - 1 Chapter 11 - Homework Solutions 11.2) What...

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1 Chapter 11 - Homework Solutions 11.2) What types of Intermolecular Attractive Forces (IAF) are shown in the following? a) HF molecules H-F ------ H-F (This dashed line represents a H-bond.) What is being shown is a hydrogen bond. This occurs between a lone-pair of electrons on the F atom of one molecule and the H atom of another molecule. Remember, H bonding is a special type of very strong dipole-dipole interaction. It occurs when a H atom bonded directly to a an atom of high electronegativity (N, O or F) forms a strong dipole-dipole attraction to an unshared electron pair on a nearby small electronegative atom or ion (N, O or F). You need a H covalently bonded (directly connected) to a N, O or F in a molecule in order to have hydrogen bonding and a lone pair on a N, O or F. You will also have London Forces (LF) and Dipole-Dipole AF (DD) between HF molecules. Not all HF molecules in the liquid will be H-bonded to each other. The molecules have to line up just right to form H bonds. Thus, when you have liquid HF the molecules are attracted to each other by all three types of AF (LF, DD and H-bonding). In solid HF (if it is a prefect crystalline solid) the H-bonding will be maximized and on average the HF molecules form 2 H-bonds per molecule. In the liquid the HF molecules form between 1-2 H-bonds per molecule. Polar molecules with a H bonded directly to a N, O or F atom can form H-bonds in addition to LF and DD. Thus, polar molecules are attracted to each other by LF , DD and H-bonds . b) F 2 molecules F-F --- F-F (This dashed line represents LF.) This molecule is NON polar. All molecules have LF between them. NON polar molecules have ONLY LF between them.
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2 11.2) (cont.) c) Na + and H 2 O Na + *** H 2 O (This represents a Ion-Dipole AF.) Ion-Dipole AF (I-D) occur between an ion and a polar molecule. This is a very strong IAF. It occurs in solutions and we will discuss it in detail and use it in Ch. 13. In this particular case, the negative end of the polar H 2 O (the oxygen atom) is attracted to the positive Na + cation. This AF is weaker than the Ion-Ion AF forces in ionic compounds but much stronger than H-bonding. d) SO 2 molecules O = S ----- O = S (This represents LF and DD AF) \ \ O O This molecule is polar . The S-O bonds are polar and the molecule is bent (with a bond angle of about 120°). The S atom has a partial positive charge ( * + ) on it and the O atoms have a partial negative charge ( * ). Thus, the partially negatively charged O atom of one molecule forms an attraction to the positively charged S atom of another molecule. This is in addition to LF that occur between these molecules. Thus, SO 2 molecules are attracted to each other by both LF and DD AF. Polar
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This note was uploaded on 07/17/2008 for the course CHEM 122 taught by Professor Zellmer during the Summer '07 term at Ohio State.

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122ch11a_001 - 1 Chapter 11 - Homework Solutions 11.2) What...

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