5 Steps to a 5 AP Chemistry

You get 1 point if you correctly predict only SiF 4 to be nonpolar. You get 1 additional

point for each correct Lewis structure.

b. The order is: KrF 2 <SeF 2 <SnF 2.

KrF 2 : two bonding SeF 2 : two bonding SnF 2 : ionic

pairs and three pairs and two

nonbonding pairs nonbonding pairs

The Lewis structure indicates that KrF 2 is nonpolar. Thus, it only has very weak

London dispersion forces between the molecules. SeF 2 is polar and the molecules are

attracted by dipole–dipole attractions, which are stronger than London. SnF 2 has the highest

melting point, because of the presence of strong ionic bonds.

You get 1 point for the order, and 1 point for the discussion.

c. The following resonance structures may be drawn for the oxalate ion. The presence of

resonance equalizes the bonds.

You get 1 point for any correct Lewis structure for C 2 O 42 −,and 1 point for showing or

discussing resonance.

d. PCl 5 must ionize. There are two acceptable equations.

You get 1 point for the explanation, and you get 1 point for either of the equations.

Total your points for the different parts. There are 10 points possible.

 Rapid Review

 Compounds are pure substances that have a fixed proportion of elements.

 Metals react with nonmetals to form ionic bonds, and nonmetals react with other non-

metals to form covalent bonds.

 The Lewis electron-dot structure is a way of representing an element and its valence

electrons.

 Atoms tend to lose, gain, or share electrons to achieve the same electronic configuration

(become isoelectronic to) as the nearest noble gas.

 Atoms are generally most stable when they have a complete octet (eight electrons).

 Ionic bonds result when a metal loses electrons to form cations and a nonmetal gains

those electrons to form an anion.

2 PCl 546 PCl ++++PCl or PCl– 5 PCl 4 Cl–

Sn 2

2+

F

−

F Se

F Kr F F

164  Step 4. Review the Knowledge You Need to Score High

CC

O O

O

O

O

2 −

CC

O

O O

2 −

CC

O

O

O

O

2 −

CC

O

O

O

O

2 −