Group 18- The Nobel Gases

Question 1

Why is there little chemistry seen?

Answer 1

They have a filled octet and high 1st ionisation energy

Question 2

Describe the trend of IE with increasing size ,

How does this related to reactivity

Answer 2

The ionisation energy decreases with increasing size of the atom

This means that the reactivity of the elements increases down the group

Question 3

Which is the most reactive noble gas?

Answer 3

Xenon

Question 4

Describe Xe reactions with fluorine

Answer 4

Xe + F2 -> XeF2
(Sunlight)
Xe + 5F2 -> XeF4 + 3F2
(400 Celsius, 5atm)
Xe + 20F2 -> XeF6 + 17F2
(300 Celsius, 50 atom)

XeF6 + H2O-> XeOF4 + 2HF

Question 5

How can Xe reach higher oxidation states despite the high IE?

Answer 5

It can reach them due to the formation of strong bonds which means you get the energy back that you put in to reach the higher state

Question 6

Describe the geometries of Xe F products

Answer 6

XeF2 is linear
xeF4 is square planar
XeF6 has no vesper, it is distorted octahedral ( lone pair is directed through one of the triangular faces)

Question 7

Why is XeF6 fluxional?

Answer 7

The lone pair of electrons is able to move around the oxtahedron

Question 8

Describe a useful property of Xe fluorides

Answer 8

They are strong fluoridating agents and act as fluoride ion donors and acceptors

Question 9

Use MO theory to describe the bonding in XeF2

Answer 9

Linear molecule
The 5px and 5py form 2 non bonding MOs as they are the wrong symmetry
5pz interacts with out of phase p orbitals of F to make bonding
5pz also interacts in phase p orbitals to make a non bonding orbital
The 5s makes another non bonding as it has the wrong symmetry

Question 10

What is the bond in XeF2?

Answer 10

4 centre, 3 electron bonding

The system is quite ionic with lots of ionic character in the bond

Question 11

What is the bond order of XeF2

Answer 11

1/2

Question 12

What other element can form stable compounds with F?

Answer 12

Krypton, it forms KrF2, KrF+ and Kr2F3+

Question 13

How do you form KrF2?

Answer 13

Kr +F2 -> KrF2

1) cool to 196 Celsius
2) use electric discharge- high energy electrons or rays to break F bonds

This rapidly decays- less stable than XeF2

Question 14

What argon compounds are known?

Answer 14

HArF

Question 15

How do you form HArF?

Answer 15

Ar + HF -> HArF

1) IV irradiation
2) in solid argon matrix at -233 Celsius

This is very unstable above -200 Celsius