Everything Science Grade 10

6.2 CHAPTER 6. CHEMICAL BONDING

bonding.

You need to remember that it is thevalence electrons(those in the outermost level) that are

involved in bonding and that atoms will try to fill their outer energy levels so that they are

more stable. The noble gases have completely full outer energy levels, so are very stable

and do not react easily with other atoms.

Lewis structures ESABS

Lewis notationuses dots and crosses to represent thevalence electronson different atoms.

The chemical symbol of the element is used to represent the nucleus and the inner elec-

trons of the atom. To determine which are the valence electrons we look at the lastenergy

levelin the atom’s electronic structure (chapter 4). For example, chlorine’s electronic struc-

ture can be written as: 1 s^22 s^22 p^63 s^23 p^5 or [Ne] 3 s^23 p^5. The last energy level is the third one

and it contains 7 electrons. These are the valence electrons.

Tip

If we write the con-
densed electron con-
figuration, then we
can easily see the va-
lence electrons.

For example:

A hydrogen atom (one valence electron) would be represented like this: H•

A chlorine atom (seven valence electrons) would look like this:

××Cl ××

××

×

A molecule of hydrogen chloride would be shown like this:

××Cl ××

ו ××

H

The dot and cross in between the two atoms, represent the pair of electrons that are shared

in the covalent bond.

Table 6.1 gives some further examples of Lewis diagrams.

Iodine I 2

I

××

××××

I

•• ••

ו ••

Water H 2 O

H O

ו ××

ו ××

H

Carbon dioxide CO 2

O

••

•• ••C

××

××O••

•• ••

Hydrogen cyanide HCN

H C

ו

×××

N ••

•••

Table 6.1: Lewis diagrams for some simple molecules

106 Chemistry: Matter and Materials