Covalent bonding

Question 1

What is a covalent bond

Answer 1

two non-metal atoms, sharing a pair of electrons in order to fill the outer shell.

Question 2

Electrostatic attractions in covalent bonds

Answer 2

There is a strong attraction between a shared pair of electrons and two nuclei.

Question 3

Simple molecular structure

Answer 3

Just made up of molecules
Within each molecule, are atoms bonded to each other covalently. Only covalent bonds INSIDE the molecules are strong.

Question 4

Why do simple molecular structures have a low boiling/melting point

Answer 4

Between the molecules are weak forces of attraction that require little energy to break. These forces are not covalent bonds. This is why simple molecular substances have a low boiling point.

Question 5

How does increase in relative molecular mass affect melting and boiling points in simple molecular structures

Answer 5

Larger molecules → higher boiling points.
Larger molecules (= higher molecular mass) have more forces of attraction between them. Since there are more forces, they require more/higher heat to break the bonds.

Question 6

Why substances (e.g. diamond) with giant covalent structures are solids with high melting and boiling points

Answer 6

Diamond has a high melting point because it is a giant covalent structure with many strong covalent bonds that require a lot of energy to break.

Question 7

Allotropes

Answer 7

different forms of the same element

Question 8

Examples of allotropes

Answer 8

diamond, graphite and C60 fullerene

Question 9

Diamond: how many atoms are bonded, and what type of atom

Answer 9

• made up of only carbon atoms
• all electrons are bonded

Question 10

Graphite: how many atoms are bonded, and what type of atom

Answer 10

• made up of only carbon atoms
• each carbon atom has a strong covalent bond to 3 other carbons → 1 delocalised electron

Question 11

Can graphite conduct electricity

Answer 11

Even though they are non-metal, but can conduct electricity because there are delocalised electrons that are free to move

Question 12

Graphite

Answer 12

each layer = giant structure, with weak intermolecular forces or weak forces of attraction between layers.
These layers can easily slide over each other.

Question 13

Diamond shape

Answer 13

giant 3D lattice

Question 14

diamond structure

Answer 14

Diamond is extremely hard because it is a giant covalent structure with many strong covalent bonds and strong intermolecular forces.

Question 15

Why does diamond have strong bonds and intermolecular forces?

Answer 15

strong covalent bonds to 4 other carbon → no delocalised electrons → strong intermolecular forces

Question 16

Why is graphite used as a lubricant?

Answer 16

graphite is soft/slippery, and layers will slide over each other due to the weak forces of attraction between layers.

Question 17

C60 fullerene

Answer 17

• C60 fullerene cannot conduct electricity.
• each carbon is only covalently bonded to 3 others and the other electrons are delocalised → weak intermolecular forces → less energy to overcome → lower boiling point
• simple molecular structure

Question 18

Can covalent compounds conduct electricity? Why?

Answer 18

Electric current is a flow of charged particles that can move.
Covalent compounds do not have delocalised/free electrons, so they cannot conduct electricity.