9 - Alkaline Earth Metals

Question 1

What are Group 2 elements?

Answer 1

Alkaline earth metals
As their oxides and hydroxides are alkaline.

Question 2

What are the physical properties of Group 2 elements?

Answer 2

All have 2 electrons in an outer s-orbital.
Have high melting points as they metallic bond which forms a strong electrostatic attraction between the cations and the sea of delocalised electrons.
In all reactions they lose their 2 valence electrons to form ions.

Question 3

What is the trend of atomic radius down Group 2?

Answer 3

Increases
As each element will have an extra filled shell of electrons so the shielding between the nucleus and valence electrons increases.

Question 4

What is the trend of melting points down Group 2?

Answer 4

Decreases
As the electrons in the ‘sea’ of delocalised electrons gets further away from the positive nucleus the strength of the metallic bond decreases.

Question 5

What is the trend of first and second ionisation energy down Group 2?

Answer 5

Decreases
As it takes less energy to remove the valence electrons as shielding increases, weakening the electrostatic attraction between the valence electrons and the nucleus.

Question 6

What is the trend of reactivity down Group 2?

Answer 6

Increases
Shielding increases so it is easier to lose the 2 valence electrons therefore its easier to form a cation.

Question 7

What is the trend of the elements reaction with oxygen down Group 2?

Answer 7

Reacts with increasing vigour.

Question 8

What occurs when the elements react with oxygen?

Answer 8

A metal oxide and hydrogen is formed.
The metal is oxidised (0 to +2)
The oxygen is reduced (0 to -2)

Question 9

What is the trend of the elements reaction with water down Group 2?

Answer 9

Reacts with increasing vigour.

Question 10

What occurs when the elements react with water?

Answer 10

A hydroxide[ X(OH)2 (aq) ] and hydrogen is formed.
Reacts very slowly with cold water.

Question 11

What occurs when the elements react with steam?

Answer 11

A metal oxide is formed
Reacts rapidly.

Question 12

What is magnesium hydroxide used for?

Answer 12

Indigestion tablets to neutralise stomach acid.

Question 13

What is calcium hydroxide used for?

Answer 13

To treat acidic soil by neutralising it.

Question 14

What is the trend of the basic strength of hydroxides down Group 2?

Answer 14

Increases
As solubility increases the more the hydroxides dissociates in water, releasing more hydroxide ions

Question 15

What is basic strength of element?

Answer 15

The ability of a substance to accept protons (H+) or donate hydroxide ions (OH−) in an aqueous solution.

Question 16

What is the trend of the solubility of hydroxides down Group 2?

Answer 16

Increases
As the ions get larger the chare density decreases therefore there is a lower attraction between the OH- ions and the larger +2 ions so the ions split away from each other easily.

Question 17

What is the trend of the pH of hydroxides down Group 2?

Answer 17

Increases
As the more soluble the hydroxide the more they dissociate so the greater the OH- ion concentration in the water.

Question 18

What is the trend of the solubility of sulphates down Group 2?

Answer 18

Decreases
As the cation gets larger the charge density decreases therefore becoming less attracted to the polar water molecules.

Question 19

What is the solubility of Barium Sulphate like?

Answer 19

Insoluble.

Question 20

What is barium sulphate used for?

Answer 20

Used to outline the gut in medical X-rays as it is good at absorbing X-rays and is safe despite being toxic due to its insolubility.

Question 21

How is the insolubility of barium sulphate used to test for sulphate ions in solution?

Answer 21

The solution is acidified with nitric or hydrochloric acid to remove carbonate ions as carbon dioxide, as barium carbonate is also an indistinguishable while precipitate.
Barium chloride is then added and if a sulphate is present a white precipitate of barium sulphate is formed.