covalent bonding (topic 2)

Question 1

explain how these covalent bonds are formed (2)

Answer 1

• electrons are shared between nitrogen and hydrogen
• the covalent bond is a shared pair of electrons

Question 2

predict the physical state of hydrogen fluoride at room temperature and pressure, explain your answer (3)

Answer 2

• gas or liquid
• made of small molecules
• has low melting point
• has low boiling point
• forces between molecules are weak

Question 3

what is a covalent bond (2)

Answer 3

shared electrons

Question 4

what does each single line represent in the formula above

Answer 4

one covalent bond

Question 5

draw a dot and cross diagram to show the bonding in a molecule of nitrogen gas (N2)

Answer 5

Question 6

Answer 6

Question 7

draw a dot and cross diagram to show the bonding in a molecule of chlorine (Cl2)

Answer 7

Question 8

explain why chlorine and other small covalent molecules are gases at room temperature (3)

Answer 8

• the intermolecular forces between molecules are weak
• a small amount of energy is required to break the bonds
• so at room temperature molecules can move freely, so are gaseous

Question 9

(6)

Answer 9

all structures:
- show that methane contains carbon and hydrogen
structure A:
- shows the ratio of carbon atoms to hydrogen atoms as 1:4
- gives no information about the bonding in the molecule
- gives no information about the shape of the molecule
structure B:
- shows the covalent bonding between carbon and hydrogen atoms
- shows the inner shell is not involved in bonding
structure C:
- uses single lines to show single covalent bonds
structures B and C:
- do not show the 3D structure of a methane molecule
structure D:
- shows atoms connected by sticks, which is not true
- shows position in space
structures B, C and D:
- show there are only single bonds in methane
structure E:
- shows the 3D arrangement of atoms
- shows the approximate size occupied by separate atoms
- provides no information about the type of bond between atoms

Question 10

does pure water conduct electricity, explain your answer (3)

Answer 10

• no
• water molecules are neutral
• there are no charged particles to move and carry charge

Question 11

explain why carbon dioxide is a gas at room temperature (2)

Answer 11

• the intermolecular forces/bonds between carbon dioxide molecules are weak
• small amount of energy is required to break the bonds
• so molecules are free to move at room temperature, and so are gaseous

Question 12

carbon dioxide can also be represented using a displayed formula, draw the displayed formula of carbon dioxide

Answer 12

Question 13

give one advantage of the dot and cross diagram compared to the displayed formula (1)

Answer 13

the dot and cross diagram shows which atom each electron comes from

Question 14

explain the electrical conductivity of simple molecular substances such as oxygen (2)

Answer 14

• no electrical conductivity
• there are no ions or electrons free to move

Question 15

explain, in terms of structure, why oxygen is a gas, even at low temperatures (2)

Answer 15

• intermolecular forces between molecules are weak
• only a small amount of energy needed to overcome forces
• low boiling point

Question 16

(4)

Answer 16

• giant structure
• covalent bonds
• strong bonds
• each silicon atom forms 4 bonds and each oxygen atom forms 2 bonds

Question 17

Answer 17

• weaker bonds
• fewer bonds