Learning focus
Develop precise chemical language, connect particle and bonding models to observations, interpret diagrams and data, and apply ideas to unfamiliar examples.
Double bonds
A double bond contains two shared pairs, or four shared electrons. O2 has an O=O double bond. Ethene contains a C=C double bond and is unsaturated.
Triple bonds
A triple bond contains three shared pairs, or six shared electrons. N2 has a strong N triple bond N, with one lone pair on each nitrogen.
Carbon dioxide
The displayed formula is O=C=O. Carbon shares two pairs with each oxygen, so all atoms have full outer shells. Each oxygen has two lone pairs.
Formula representations
A molecular formula gives the number of each atom type. A displayed formula shows every bond. A structural formula groups atoms to show connectivity, for example CH3OH or CH2=CH2.
Bond counting
One line means one shared pair, two lines a double bond and three lines a triple bond. A double bond contains four electrons, not two.
Practical or data skill
Translate between molecular, structural, displayed and dot-and-cross forms for O2, N2, CO2, ethene and methanol.
Examination tip
Count shared pairs rather than bond lines only when the question asks for electrons.
Review questions and suggested answers
Question 1
Electrons in a double bond?
Suggested answer
Four.
Question 2
Bond in N2?
Suggested answer
Triple covalent bond.
Question 3
Displayed formula of CO2?
Suggested answer
O=C=O.
