Covalent Bonding
6 marks · NormalThis question is about covalent bonds and giant covalent structures.
Define a covalent bond.
Describe what holds the atoms together in a covalent bond.
Diamond and graphite both contain carbon atoms joined by covalent bonds. State one way in which their structures are similar and one way in which they are different.
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(a) A covalent bond is formed when two atoms share a pair of electrons. · must show sharing, pair of electrons, between two atoms
(b) The atoms are held together by the strong electrostatic attraction between the positive nuclei and the shared pair of electrons. · must show strong electrostatic attraction, nuclei, shared pair of electrons
(c) Similar: Both have carbon atoms covalently bonded in a giant structure. Different: Diamond has each carbon joined to 4 others in a 3D tetrahedral structure; graphite has each carbon joined to only 3 others in layers. · must show both giant covalent, diamond: 4 bonds, tetrahedral, graphite: 3 bonds, layers
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Marking points
M1 (a) · 1 mark · States the sharing of electrons or pairs of electrons.
A1 (a) · 1 mark · Specifies this occurs between two atoms.
M2 (b) · 1 mark · Mentions electrostatic attraction or force between nuclei and shared electrons.
A2 (b) · 1 mark · Correctly links the positive nuclei and the negative shared electron pair.
B1 (c) · 1 mark · States a similarity, e.g. both have a giant covalent structure.
B2 (c) · 1 mark · States a difference, e.g. diamond has four bonds, graphite has three bonds/layers.
Worked solution
a) A covalent bond is formed when two atoms share a pair of electrons.
b) The atoms are held together by the strong electrostatic attraction between the positive nuclei and the shared pair of electrons, which are negatively charged.
c) Similarity: Both diamond and graphite are giant covalent structures made of carbon atoms covalently bonded together. Difference: In diamond, each carbon atom is bonded to four others in a tetrahedral 3D structure; in graphite, each carbon atom is bonded to three others in layers.