Group 17- The Halogens

Question 1

What is the outer electron configuration?

Answer 1

ns2np6

Question 2

What are halogens most commonly found as?

Answer 2

Halide anions where an electron has been gained

X + e- -> X-

This is exothermic

Question 3

Describe the trend in oxidising power

Answer 3

All halogens are oxidising agents but the oxidising power decreases as you go down the group due to the decrease in electronegativity
I- can even be used as a reducing agent

Question 4

Describe the trend in stability of the halides

Answer 4

Stability decreases as the size of the halogen decrease

Question 5

Why does F has a different electron gain enthalpy than expected?

Answer 5

On the basis of electronegativity we would expect F to have the smallest electron gain energy
But F is very small which leads to electron repulsions which means adding an electron requires more energy

Question 6

Why do larger halogens have weaker bonding?

Answer 6

Large atoms means they have more large diffuse orbitals which leads to poorer orbital overlap and so weaker bonding

Question 7

Why is the F-F bond weaker than expected?

Answer 7

You would expect F bond to be strong as it is small

But there are electron repulsions due to the small size of F which makes the bond unstable

Question 8

What are interhalogen compounds?

Answer 8

Interhalogen compounds contain two or more different halogens

Question 9

Why is it easier to oxidise halogens at the bottom of the group?

Answer 9

This is because they have a lower ionisation energy at the bottom of the group

Question 10

Which oxidation state forms the strongest bonds ?

Answer 10

+6 forms strong bonds

You get the same energy in an you get out which allows the element to reach the oxidation state +6

Question 11

What at the properties of interhalogen compounds?

Answer 11

Strongly oxidising

Hypervalent

Question 12

What are the formulas of the interhalogen compounds that can be formed?

Answer 12

XY, XY3, XY5, IF7

X is the most electropositive halogen and is the central atom
Y is normally F as it is the most electronegative

Question 13

What are compounds known for XY

Answer 13

All combinations of halogens are known for this

Question 14

Which compounds are known for XY3

Answer 14

X is the +3 oxidation state
Y= F
X= Cl, Br or I

This requires higher heating, pressure and good oxidising agents

Question 15

Which compounds are known for XY5

Answer 15

Only ClF5, BrF5 and IF5 are possible

Question 16

How are halogens able to reach higher oxidation states?

Answer 16

The bonds are strong which replaces the energy required to reach the higher oxidation state

Question 17

Which compounds are possible for XY7

Answer 17

Only IF7 exists

A very high temperature is required

Question 18

Use MO theory to describe the bonding in [F-H-F]-

Answer 18

Bonding orbitals- 2 F p orbitals being in phase with each other and the S orbital being in phase with these
Antibonding- 2F p orbitals are in phase with each other, S is out of phase
Non bonding- 2F p orbitals are out of phase with each other so H has the wrong symmetry to interact

Question 19

Describe the bond in FHF-

Answer 19

It is a 3 centre, 4 electron bond

There are 4 electrons in the bonding, two electrons from the two Fs, one from the hydrogen and one from the negative charge