What is a covalent bond?
4 marks · Normal| Molecule | Number of Covalent Bonds per Molecule |
|---|---|
| H2 | 1 |
| CH4 | 4 |
| NH3 | 3 |
| CO2 | 4 |
Using the data in Table 1, answer the following questions:
Which molecule contains the greatest number of covalent bonds per molecule?
Explain why CO has four covalent bonds per molecule.
State how many covalent bonds exist in two molecules of ammonia (NH).
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) CH and CO (tie for 4 bonds).
(b) In CO, the carbon atom forms a double bond with each oxygen atom, giving a total of four shared electron pairs (two bonds per oxygen × 2 = 4 bonds).
(c) 6
Common mistakes: Thinking ammonia has 6 bonds in one molecule.; Misidentifying the double bonds in CO2.
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · Identifies CH4 or CO2 as having the highest number of covalent bonds (either is accepted as both have 4).
M1 (b) · 1 mark · States carbon forms a double bond to each oxygen (total two double bonds).
A2 (b) · 1 mark · Correctly states total: 2 bonds per O × 2 O = 4 bonds in CO2.
N1 (c) · 1 mark · Two NH3 molecules have 3 bonds each: total = 6.
Worked solution
a) CH4 and CO2 both have 4 covalent bonds per molecule, which is the greatest.
b) In CO2, carbon forms two double covalent bonds (one to each oxygen), so there are 2 × 2 = 4 bonds in total.
c) Two NH3 molecules have 3 × 2 = 6 covalent bonds in total.