What is a covalent bond?
4 marks · NormalDraw a dot-and-cross diagram to show the covalent bonding in an oxygen (O) molecule.
Explain why there are two covalent bonds between the two oxygen atoms.
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.
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(a) Dot-and-cross diagram for O2 with two shared pairs between the O atoms, and two lone pairs on each O. · must show 2 O atoms, 2 shared pairs between, 2 lone pairs on each O.
(b) Each oxygen atom has 6 electrons in its outer shell and needs to share 2 electrons to get 8; both share 2 electrons, forming two shared pairs (double bond).
Must show: O2 diagram: two shared pairs
Also accept: Any clear representation of two shared pairs between O atoms.; Dots/crosses may be in any distinct symbols.
Common mistakes: Only drawing one shared pair.; Not showing lone pairs.
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Marking points
D1 (a) · 1 mark · Two oxygen atoms drawn with two shared pairs between them.
D2 (a) · 1 mark · Each O has two lone pairs.
M1 (b) · 1 mark · States each O atom needs to share two electrons to get 8 in its outer shell.
A1 (b) · 1 mark · Explains two shared pairs means a double covalent bond.
Worked solution
b) Each oxygen atom needs to gain 2 electrons to have a full outer shell (8 electrons), so they each share 2 electrons with each other, forming two shared pairs—this makes a double covalent bond.