Principles of Chemistry - Covalent Bonding

Question 1

what is a covalent bond formed between?

Answer 1

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

Question 2

what is covalent bonding?

Answer 2

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

Question 3

why are substances with simple molecular structures gases, liquids, or solids with low melting points?

Answer 3

• 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

Question 4

why does the melting point of substances with simple molecular structures increase with relative molecular mass?

Answer 4

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

Question 5

why are giant covalent structures solids with high melting points?

Answer 5

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

Question 6

how does the structure of diamond influence its physical properties?

Answer 6

• 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.

Question 7

how does the structure of graphite influence its physical properties?

Answer 7

• 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

Question 8

how does the structure of C60 fullerene influence its properties?

Answer 8

• 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.

Question 9

do covalent compounds conduct electricity?

Answer 9

no