3.1

Question 1

Explanation of the nooks in ionisation energies due to sub shells

Answer 1

There is a slight decrease in first ionisation energy between beryllium and boron as the fifth electron in boron is in the 2p subshell, which is further away from the nucleus than the 2s subshell of beryllium

There is a slight decrease in first ionisation energy between nitrogen and oxygen as the paired electrons in the 2p subshell of oxygen repel each other, making it easier to remove an electron in oxygen than nitrogen.
Nitrogen has a first ionisation energy of 1402 kJ mol-1 as its electron configuration is 1s2 2s2 2p3
Oxygen has a first ionisation energy of 1314 kJ mol-1 as its electron configuration is 1s2 2s2 2p4

Question 2

Prediction of electron configurations having been given the ionisation energies

Answer 2

High difference in energies = the electron is being removed from a different shell closer to the nucleus

Question 3

Variations in melting points across periods 2 and 3 in terms of structures and bonding

Question 4

Redox reactions and reactivity with group 2 metals:

Answer 4

All group 2 metals have an outer shell with only 2 electrons, both in that shell’s s orbital. Electronic stability is gained by losing both these electrons leaving them with a 2+ charge. This makes them quite good reducing agents.

Question 5

How can the relative reactivities of group 2 elements be show?

Answer 5

Due to increasing atomic radii and increasing electron shielding, the ionisation energy decreases as you go down the group and therefore the reactivity increases.
This can be shown by how they react with:
1. Oxygen: Group 2 Metal + Oxygen → White Ionic Metal Oxide (calcium burns with a brick-red flame)
2. Water: Group 2 metal + Water → Metal Hydroxide + Hydrogen
Beryllium does not react with water.
Magnesium only reacts with very hot water when ground into a very fine powder.
As you go down the group they react faster. They slowly dissolve and disappear. Effervescence and steam may be seen. The grains of metal may rise and fall in the test-tube as hydrogen bubbles form around the grains and then escape upon reaching the surface. A white precipitate is seen as hydroxides are insoluble.
3. Metal + acid → salt + hydrogen
They react vigorously.

Question 6

What happens when water is added to group 2 oxides?

Answer 6

Metal Oxide + Water → Metal Hydroxide solution
The solubility of the metal hydroxide increases as you go down the group.
The more soluble the hydroxide the more OH- ions available per mole of Metal Hydroxide dissolved, so the more alkaline they are.
On the pH scale: Magnesium is ~8. All the others are ~12.

Question 7

Uses of group 2 compounds as bases:

Answer 7

• Mg(OH)2 and CaCO3 as antacids in treating indigestion.
  -Ca(OH)2 in agriculture to neutralise acid soils.

Question 8

What is the trend in boiling points amounts the halogens?

Answer 8

At room temperature: F2 and Cl2 are gases, Br2 is a liquid, and I2 is a solid.
This is because the X-X bond is non-polar as both atoms are of the same element so have the same electronegativity, so the only intermolecular forces possible are London Dispersion forces, which increase in strength with the increased numbers of electrons.

Question 9

Redox reactions and reactivity of halogens and their compounds:

Answer 9

Halogens have an electron configuration ending in s2p5, so they from 1- ions, making them good oxidising agents.
As always, atomic radius and electron shielding outweigh nuclear charge so Fluorine attracts electrons more strongly than Iodine, making it more reactive.
This can be proved by displacement reactions: add KX1 to X2 in a test tube.
Cl2 is slightly green/yellow, Br2 is orange, and I2 is brown.
Organic solvents, like cyclohexane, turn iodine from purple to brown.

Question 10

What is the word for a reaction in which one element is both oxidised and reduced? +examples

Answer 10

Disproportionation.
The reaction of chlorine with water as used in water treatment:
Cl2(aq) + H2O(l) ⇌ HCl(aq) + HOCl(aq)
The reaction of chlorine with sodium hydroxide to form bleach:
2NaOH + Cl2 –> NaCl + NaOCl + H2O

Question 11

What are the benefits and drawbacks to using chlorine in water treatment?

Answer 11

-kills bacteria e.g. cholera thereby saving lives
-hazards of toxic chlorine gas and risks from the formation of chlorinated hydrocarbons.

Question 12

What are the tests for different halide ions?

Answer 12

Ion : silver nitrate : dilute ammonia : concentrated ammonia
F- : no visible change
Cl- : white precipitate : colourless solution
Br- : cream precipitate : cream precipitate : colourless solution
I- : yellow precipitate : yellow precipitate : yellow precipitate

Question 13

What is the test for carbonate ions?

Answer 13

Carbonates react with dilute acids to make carbon dioxide which can be identified by effervescence or tested with lime water.

Question 14

What is the test for sulphate ions?

Answer 14

Barium sulphate is insoluble, so we add a soluble barium compound (usually barium chloride) and if it forms a white precipitate sulphate ions are present.

Question 15

What is the order for chemical tests?

Answer 15

1. carbonate
2. sulphate
3. halide

Question 16

What is the test for ammonium ions?

Answer 16

Add sodium hydroxide which produces a white fume of ammonia gas which can then be tested for by using damp red litmus paper which should then turn blue.