Group 16- The Chalcogens

Question 1

What is the outer electron configuration?

Answer 1

ns2np4

Question 2

Describe the trend in metallic character

Answer 2

Metallic character increases as the group descends

Question 3

What is the highest oxidation state?

Answer 3

+6

Question 4

What species do they like to form?

Answer 4

X2-

Question 5

Describe the 1st and 2nd electron gain enthalpy?

Answer 5

The 1st is exothermic and the 2nd is endothermic

However energy is received back from the formation of ionic or covalent bonds

Question 6

Describe the boiling points from H2S to H2Se

Answer 6

The boiling points increase due to greater van der waals forces

Question 7

Why is the boiling point of H2O high?

Answer 7

It is high due to hydrogen bonding

Question 8

Why is does SF6 break the octet rule?

Answer 8

S has 6 electrons and each f donates an electron

In total there are 12 valence electrons which breaks the octet rule?

Question 9

Why is SF6 unreactive with water?

Answer 9

The f shields s from attack

Question 10

What is the synthesis of SF6?

Answer 10

S8 + 24F2 -> 8SF6

Question 11

What are the properties or SF6?

Answer 11

\+6 oxidation state
Colourless
Odourless
Inert
Non toxic
Non flammable 
Breaks octet rule

Question 12

Describe the geometry of SF6

Answer 12

6 bonding pairs so it is octahedral

Sp3d hybridisation is a poor way of account for its hyper valency

Question 13

Describe the orbitals involved in bonding for SF6

Answer 13

S has 3s, 3pxyz
Each f uses a single p orbital

That means there are 10AO and so therefore 10 molecular orbitals

Question 14

Describe the MO that make up the bonding in SF6

Answer 14

10 AO means there are 10 MO

4 are bonding
4 are antibonding
2 are non bonding

Question 15

How are the bonding orbitals formed in SF6?

Answer 15

A bonding MO is made with the f p orbitals and the S 3s orbital all in phase with each other
3 degenerate bonding MOs are made with the p orbitals of f and the 3 x3p orbitals of S being in phase with each other

Question 17

How are the antibonding orbitals made in SF6

Answer 17

An antibonding MO is made with the f p orbitals being in the same phase as the bonding MO but the S 3s is now out of phase with these
3 more antibonding MO are made with the f p orbitals being in the same phase as the bonding MO but the S 3x 3p is now out of phase with these

Question 18

How do you calculate bond order?

Answer 18

BO= (Bonding- antibonding)/2

Question 19

What is the bond order of SF6?

Answer 19

8-0/2 =4

This is spread over all 6 F= 2/3
No electrons occupy antibonding
8 electron will occupy bonding, 4 will occupy non bonding

Question 20

How does the MO orbitals explain the hypervalency in SF6?

Answer 20

8 electrons occupy bonding
4 electrons occupy non bonding
This means 8 of the 12 electrons occupy bonding so the octet rule still applies and the molecule can exist

Question 21

Why is SBr6 unknown when we have SF6?

Answer 21

Four electrons are placed entirely on electronegative fluorine atoms so it is stabilised
Br isn’t as electronegative
S-F bonds may be stronger

Question 22

How are the non bonding MO orbitals made?

Answer 22

There is no contribution from S, these are entirely based on F