Week 6 · Lesson 4 Chemical Bonds: ions and the ionic bond, the covalent bond, ionic and covalent compounds, carbon and methane · 3 lessons
2
Sharing electrons: the covalent bond
Science Prep 1 Term 1, Unit 1: pp. 26–31
GoalExplain how nonmetal atoms share electrons in covalent bonds and draw single, double and triple bonds.
New words
covalent bond · a bond formed when two atoms share electronssingle bond · one shared pair of electronsdouble bond · two shared pairs of electronstriple bond · three shared pairs of electrons
Explanation
Two nonmetal atoms both tend to gain electrons, so neither gives one away. Instead they share. A pair of electrons shared between two atoms is a covalent bond, and each atom counts the shared pair as its own, so both reach a full outer level. One shared pair is a single bond, two pairs make a double bond and three pairs make a triple bond. We draw a bond as a line. Hydrogen chloride H–Cl has a single bond. Hydrogen H₂ has a single bond: H–H. Oxygen O₂ has a double bond: O=O. Nitrogen N₂ has a triple bond: N≡N. Water has two single bonds, one from the oxygen atom to each hydrogen atom.
Worked examples
Hydrogen has 1 outer electron and chlorine has 7. They share one pair: hydrogen now feels like helium (2) and chlorine feels like argon (8). That is the single bond in HCl.
An oxygen atom has 6 outer electrons and needs 2 more. Two oxygen atoms share two pairs, which gives a double bond in O₂.
A nitrogen atom has 5 outer electrons and needs 3 more. Two nitrogen atoms share three pairs, which gives the triple bond in N₂.
Class activity
Share the ball. Two children hold one ball between them to show a shared pair. Then show a double bond with two balls shared and a triple bond with three. Draw Cl₂ on paper: each chlorine has 7 outer electrons, so one shared pair is enough. Write its picture as Cl–Cl.
Practice
1
How many pairs of electrons are shared in O₂?
Two pairs, so it is a double bond.
2
Which molecule has a triple bond: H₂, O₂ or N₂?
N₂.
3
How many single bonds does a water molecule have?
Two: one from oxygen to each hydrogen.
4
Do covalent bonds form between two metals or between two nonmetals?
