Everything Science Grade 11

CHAPTER 1. ATOMICCOMBINATIONS 1.5

The electron configuration of hydrogen is 1s^1 and the electron configuration for

oxygen is 1s^2 2s^2 2p^4. Each hydrogen atom has one valence electron, which is

unpaired, and the oxygen atom has six valence electrons with two unpaired.

H• O

× ××

××

×

2

Step 2 : Arrange the electrons so that the outermost energy level of each atomis full.

The water molecule is represented below.

H O

ו ××

××

ו

H

Example 5: Lewis notation: Molecules with multiple bonds

QUESTION

Represent the moleculeHCN using Lewis notation

SOLUTION

Step 1 : For each atom, determine the number of valence electrons that the atom has

from its electron configuration.

The electron configuration of hydrogen is 1s^1 , the electron configuration of ni-

trogen is 1s^2 2s^2 2p^3 and for carbon is 1s^2 2s^2 2p^2. This means that hydrogen

has one valence electron which is unpaired, carbon has four valence electrons,

all of which are unpaired, and nitrogen has fivevalence electrons, threeof which

are unpaired.

H• C

×

×

×

×

N

•

••

•

Step 2 : Arrange the electrons in the HCN molecule sothat the outermost energy level

in each atom is full.

The HCN molecule is represented below. Notice the three electron pairs be-

tween the nitrogen andcarbon atom. Becausethese three covalent bonds are

between the same two atoms, this is a triple bond.

H C

ו

×××

N ••

•••