Chemistry - A Molecular Science

Chapter 4 The Ionic Bond

its oxidation state in HCl is +1. Similarly, the more electronegative chlorine would accept the electron to become a -1 ion, so its oxidation state in HCl is -1. In ClF (Figure 4.4b), the chlorine orbitals are above those of the

more electronegative fluorine, so an electron

would have to transfer from chlorine to fluorine and produce Cl

1+ and F

1- ions. Thus, the

oxidation states of Cl and F in ClF are +1 and -1

, respectively. It is important to recognize

that neither HCl nor ClF is ionic and the atom

s do not have +1 or -1 charges. However,

oxidation states are a convenient way to count electrons.

Atoms are assumed to lose and gain electrons when determining oxidation states just

as they do when they form ions. Thus, the mo

re electronegative element fills its sublevels,

while the less electronegative element empties its sublevels. Example 4.5

Consider the valence energy level diagrams for A, B, and C shown in the margin.

a) What are the likely oxidation states of A and B when they bond?

B is more electronegative, so it would be assigned the bonding electrons. It needs three electrons to fill its valence shell, so it would attain a -3 oxidation state. A would lose its one valence electron to empty its valence sh

ell and attain a +1 oxidation state.

b) What are the likely oxidation states of B and C when they bond?

C is more electronegative than B, so B would

either empty its p sublevel to become +3 or

empty the entire valence shell to become +5. C would fill its valence shell by gaining two electrons to attain a -2 oxidation state. We will use these oxidation states in Exampl

e 4.7 to determine the ratio in which the

atoms must combine in their compounds. Atoms fill or empty their valence sublevels, so the possible oxidation states of an atom

can be predicted from its group number just as the charge of an ion can be predicted.

The oxidation states that can be realized by an element

can range from minus the number

of electrons required to fill its valence shell to plus the number of electr

ons that must be lost

to empty its valence shell.

Energy

A B C^

Example 4.5

Chlorine is highly electronegative and is usually assigned the bonding electrons, but it

is a Group 7A element, so it can only accept one electron before filling its valence shell. Therefore, Cl is usually found in the -1 oxidation state. However, both F and O are more electronegative than Cl, so the bonding electr

ons would be assigned to F and O, not Cl. In

this situation, the chlorine atom would lose el

ectrons to attain a positive oxidation state. It

© by

North

Carolina

State

University