module 2 ppqs

Question 1

5) what is meant by the term ‘ionic lattice’? [2]

Answer 1

• repeating pattern
• of oppositely charged ions

Question 2

5) explain the different boiling points of NH₃, F₂ and Br₂ using the table [5]

Answer 2

• NH₃ has hydrogen bonding
• F₂ and Br₂ have london forces
• forces are intermolecular for ammonia, fluorine or bromine
• london forces in Br₂ are greater than in F₂ because bromine has more electrons than fluorine
• london forces in Br₂ are greater than hydrogen bonding in NH₃ and hydrogen bonding in NH₃ is stronger than london forces in F₂ (probably in table)

Question 3

6) explain why the student might expect the H–N–H bond angle to be larger in H₃NBF₃ than in NH₃ [3]

Answer 3

• NH₃ has three bonding pairs and one lone pair
• H₃NBF₃ has four bonding pairs and no lone pairs
• lone pair of electrons repels more than bonding pairs

Question 4

state one reason why chlorine should not be added to drinking water and one reason why it should be

Answer 4

• chlorinated hydrocarbons are carcinogens
• chlorine is toxic/poisonous
• chlorine sterilises water
• chlorine kills bacteria

Question 5

6) what is meant by the term electronegativity? [2]

Answer 5

• the ability of an atom to attract electrons
• in a covalent bond

Question 6

use your diagrams to explain why a molecule of BF₃ has bond angles of 120° and NH₃
has bond angles of 107° [5]

Answer 6

(2 for diagram)

• electron pairs repel
• NH₃ has one lone pair and three bonding pairs of electrons and lone pairs of electrons repel more than than bonding pairs
• BF₃ has three bonding pairs of electrons which repel equally

Question 7

4) what does the term ‘anhydrous’ mean? [1]

Answer 7

there are no waters of crystallisation

Question 8

what type of reaction takes place when aqueous silver nitrate is added to chlorine? [1]

Answer 8

precipitation reaction

Question 9

5) explain how the information in the table above provides evidence for two electron
shells in oxygen [2]

Answer 9

• large difference between 6th and 7th IEs
• marking a different shell closer to nucleus

Question 10

5) why is bromine classified as a p-block element? [1]

Answer 10

the highest energy sub-shell being filled is the p sub-shell

Question 11

6) with an example, how can the presence of a polar bond be explained in terms of electronegativity? [2]

Answer 11

• one element is more electronegative than the other
• δ- on more electronegative atom and δ+ on less

Question 12

5) explain why silicon has a much higher boiling point than phosphorus [2]

Answer 12

• in silicon, strong covalent bonds between atoms are broken
• in phosphorus, weak london forces are broken

Question 13

5) explain why the boiling point increases from sodium to aluminium [2]

Answer 13

• from Na to Al, the number of delocalised electrons increases
• metallic bonding gets stronger

Question 14

6) explain why a water molecule has a different shape from a carbon dioxide molecule [2]

Answer 14

• oxygen in water has 2 bonded pairs and 2 lone pairs AND carbon in carbon dioxide has 2 bond regions
• electron pairs repel

Question 15

5) describe the relative energies of the 2s orbital and each of the three 2p orbitals in a nitrogen atom [2]

Answer 15

• p-orbitals have greater energy than s-orbitals
• three p-orbitals have equal energy