Topic 3 - physical properties

Question 1

Melting and Boiling point

Answer 1

Melting point – sufficient energy has been added to overcome some of the attractive forces holding the atoms or molecules together​

Boiling point – sufficient energy has been added to overcome most of the rest of the attractive forces​

The stronger the forces between atoms or molecules, the higher the melting and boiling points will be

Question 2

Melting and boiling points in group 1​

Answer 2

As you go down group 1, melting and boiling points decrease​

The forces of attraction between atoms are getting weaker​

The atoms are held together by metallic bonds – the attraction between the nucleus and delocalised electrons​

As the atoms get bigger, the increase in distance from nucleus to outer orbitals makes the attraction weaker​

The increase in nuclear charge as you go down the group is offset by the increase in shielding from inner electrons

Question 3

Melting and boiling points in Group 7

Answer 3

As you go down group 7, the melting and boiling points increase​

The attractive forces are getting stronger​

The intermolecular forces between diatomic halogen molecules are temporary dipole-dipole interactions​

The bigger the atoms, the more electrons there are to move around and cause the temporary dipoles​

This means the bigger the atoms, the stronger the intermolecular forces, so more energy is needed to overcome them

Question 4

Period 2

Answer 4

Lithium to Boron:​
Metallic structure – positive ions and delocalised electrons​
More delocalised electrons = stronger bonding​
M.p. and b.p. increase​

Carbon:​
Giant covalent structure – diamond, graphite or fullerene​
Lots of strong covalent bonds to overcome​
Very high m.p. and b.p.​

Nitrogen to Fluorine:​
Small covalent molecules (N2, O2, F2)​
Only weak intermolecular forces to overcome​
Low m.p. and b.p​

Neon:​
Monoatomic, very weak intermolecular forces​
Lowest m.p. and b.p. of the period

Question 5

Period 3​

Answer 5

Similar trend to P2​

BUT non-metals in this group form different sized molecules​

Phosphorus is P4, Sulfur is S8, Chlorine is Cl2, Argon is monoatomic​

The bigger the molecule, the stronger the Van der Waals forces​

Therefore Sulfur has the highest m.p. and b.p. of the non-metals

Question 6

Trends in conductivity

Answer 6

Metals conduct both heat and electricity well as the energy (thermal or electrical) can be transferred by the delocalised electrons in the structure​

Non-metals have no delocalised electrons so cannot conduct electricity or heat​

Some semi-metals can conduct electricity a little

Question 7

Malleability and ductility​

Answer 7

Metals:​
The layers in a metal can slide over each other, making metals both malleable and ductile​

The metallic bonds are not broken by this movement of atoms, the attraction between ions and delocalised electrons remains strong​

Non-metals:​
These bond in different ways and atoms have fixed positions within their structures​

The bonding in non-metals must be overcome to move the atoms​

This means that non-metals are brittle