5 Steps to a 5 AP Chemistry

of electrons, as the closest noble gas. There are numerous exceptions to the

octet rule; for example, some atoms may have more than an octet.

Keywords and Equations

There are no keywords or equations on the AP exam specific to this chapter.

Lewis Electron-Dot Structures

The Lewis electron-dot symbol is a way of representing the element and its valence elec-

trons. The chemical symbol is written, which represents the atom’s nucleus and all inner-

shell electrons. The valence, or outer-shell, electrons are represented as dots surrounding the

atom’s symbol. Take the valence electrons, distribute them as dots one at a time around the

four sides of the symbol and then pair them up until all the valence electrons are distrib-

uted Figure 11.1 shows the Lewis symbol for several different elements.

The Lewis symbols will be used in the discussion of bonding, especially covalent bond-

ing, and will form the basis of the discussion of molecular geometry.

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

Na Mg C N F

Figure 11.1 Lewis electron-dot symbols for selected elements.

Ionic and Covalent Bonding

Ionic Bonding

Ionic bondingresults from the transfer of electrons from a metal to a nonmetal with the

formation of cations (positively charged ions) and anions (negatively charged ions). The

attraction of the opposite charges forms the ionic bond. The metal loses electrons to form

a cation (the positive charge results from having more protons than electrons), and the

nonmetal becomes an anion by gaining electrons (it now has more electrons than protons).

This is shown in Figure 11.2 for the reaction of sodium and chlorine to form sodium

chloride.

The number of electrons to be lost by the metal and gained by the nonmetal is deter-

mined by the number of electrons lost or gained by the atom in order to achieve a full octet.

There is a rule of thumb that an atom can gain or lose one or two and, on rare occasions,

three electrons, but not more than that. Sodium has one valence electron in energy level 3.

Na Na+

NaCl

Sodium chloride

++Cl Cl−

Metal Nonmetal Cation Anion

Figure 11.2 Formation of sodium chloride.

KEY IDEA