principles of chemistry - covalent bonding

Question 1

what is a covalent bond?

Answer 1

a chemical bond that involves the sharing of electrons to form electron pairs between atoms.

Question 2

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

Answer 2

Very little energy is needed to overcome the intermolecular forces

Question 3

why do the melting and boiling points of substances with simple molecular
structures increase with increasing relative molecular mass?

Answer 3

The stronger the intermolecular attractive forces, the more energy that is required to break them apart

Question 4

do covalent compounds conduct electricity?

Answer 4

no

Question 5

why do simple molecular structures have low melting and boiling points?

Answer 5

the forces of attraction between the molecules are weak, so they require little energy to break. THESE FORCES ARE NOT COVALENT BONDS

Question 6

why are giant covalent structures solid with high melting/boiling points

Answer 6

because they have many strong covalent bonds, which require a lot of energy to break.

Question 7

structure of diamond and how they influence physical properties

Answer 7

• made up of only carbon atoms
• each of those atoms has a strong covalent bonds to 4 other carbon
• every one of carbon’s 4 outer electrons is involved in one of these strong covalent bonds.
• diamond is extremely hard because it is a giant covalent structure with many strong covalent bonds.
• because it is hard, diamond is used in high speed cutting tools, eg diamond-tipped saws.

Question 8

structure of graphite and how they influence physical properties

Answer 8

• made of only carbon atoms, and is a giant structure
• it is formed of layers where each carbon atom has a strong covalent bond to 3 other carbons
• each carbon atom has one electron not involved in a covalent bond
• 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. These layers can easily slide over each other.
• graphite is soft and slippery because it has weak forces of attraction between layers.
• It is used as a lubricant and in pencils because it is soft and slippery.

Question 9

structure of C60 fullerene and how they influence physical properties

Answer 9

• a simple molecular structure (also known as a buckyball) - –
• 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.
• Hence C60 fullerene has a low melting point, and it is soft.
• C60 fullerene cannot conduct electricity.
• Although in each molecule every carbon is only covalently bonded to 3 others and the other electrons are delocalised, these electrons cannot jump between different molecules.