Everything Science Grade 11

CHAPTER 1. ATOMICCOMBINATIONS 1.4

Example 1: Covalent bonding

QUESTION

How do hydrogen and chlorine atoms bond covalently in a molecule ofhydrogen chloride?

SOLUTION

Step 1 : Determine the electronconfiguration of each of the bonding atoms.

A chlorine atom has 17electrons, and an electron configuration of [Ne] 3 s^23 p^5.

A hydrogen atom has only 1 electron, and an electron configuration of 1 s^1.

Step 2 : Determine the number of valence electrons for each atom, and howmany of

the electrons are pairedor unpaired.

Chlorine has 7 valenceelectrons. One of theseelectrons is unpaired. Hydrogen

has 1 valence electron and it is unpaired.

Step 3 : Look to see how the electrons can be sharedbetween the atoms so that the

outermost energy levelsof both atoms are full.

The hydrogen atom needs one more electron tocomplete its valence shell. The

chlorine atom also needs one more electron to complete its valence shell. There-

fore one pair of electrons must be shared betweenthe two atoms. In otherwords,

one electron from thechlorine atom will spend some of its time orbiting the

hydrogen atom so thathydrogen’s valence shell is full. The hydrogenelectron

will spend some of its time orbiting the chlorineatom so that chlorine’s valence

shell is also full. A molecule of hydrogen chloride is formed. Notice the shared

electron pair in the overlapping orbitals.

H +

x

x x

x

x

x x

Cl H

x

x x

x

x

x x

Cl

unpaired electrons

paired electrons in valence energy level

overlap of electron orbitals and

sharing of electron pair

Example 2: Covalent bonding involving multiple bonds

QUESTION

How do nitrogen and hydrogen atoms bond to form a molecule of ammonia (NH 3 )?