Principles of Chemistry - Covalent Bonding

two non-metal atoms by sharing a pair of electrons to fill the outer shell

a strong attraction between a shared pair of electrons and two nuclei

• within each molecule are atoms bonded to each other covalently. these covalent bonds inside the molecules are strong. • between the molecules are weak intermolecular forces of attraction that require little energy to break. these forces are not covalent bonds

• larger molecules (molecules with more mass) have more forces of attraction between them • these forces must be overcome if the substance is to boil

giant covalent structures have many strong covalent bonds that require a lot of energy to break

• diamond is made up of only carbon atoms, in a giant 3D lattice, where each of those atoms has strong covalent bonds to 4 other carbons • diamond is extremely hard because it is a giant covalent structure with many strong covalent bonds. this is why diamond is used in high speed cutting tools.

• graphite is also made of only carbon atoms, and is also a giant structure, but it is formed of layers where each carbon atom has a strong covalent bond to 3 other carbons. • this means each carbon atom has one electron not involved in a covalent bond, and these electrons form a sea of delocalised electrons between the layers. • graphite can conduct electricity because the delocalised electrons are free to move • each layer is a giant structure, with weak forces of attraction between the layers so they can slide over each other. this is why it’s used as a lubricant and in pencils

• C60 fullerene (simple molecular structure) is made of only carbon atoms, but it forms molecules of 60 carbon atoms. • the molecule has weak intermolecular forces of attraction between them which take little energy to overcome, so C60 fullerene is soft and has a low melting point. • C60 fullerene cannot conduct electricity as electrons cannot jump between different molecules.

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