3.1.9 Group 2 Compounds: Reactions

Question 1

What ions do group 2 elements form?

Answer 1

1. They form cations, that are +2 ions - as all of them have two outer shell electrons;
2. They do this so that they have the electron configurations of noble gasses;

Question 2

What is the electron configuration of Be, compared with its atom?

Answer 2

• Be atom electron configuration: 1s22s2;

- Be ion electron configuration: 1s2 (same as H);

Question 3

What is the electron configuration of Mg compared with its atom?

Answer 3

• Mg atom electron configuration: 1s22s22p63s2;

- Mg ion electron configuration: 1s22s22p6 (same as Neon);

Question 4

What is the electron configuration of Ca, compared with its atom?

Answer 4

• Ca atom electron configuration: [Ar] 4s2;

- Ca ion electron configuration: 1s2 (Argon);

Question 5

How does shielding change down G2?

Answer 5

1. There are more electrons added further down the group;
2. These electrons repel each other (same charges);
3. The more are added, the more they repel each other;
4. This repulsion works to overcome the attraction between the nucleus and the electron cloud;
5. This means that there is more shielding the further down the group that one goes;

Question 6

How does atomic radius change down the G2?

Answer 6

1. Shielding increases down the group;
2. Therefore, there is less effective nuclear charge between the electron cloud and the metal ions;
3. This means that the inner electrons are less attracted to the nucleus, and so the atomic radius increases, as there is less force holding the nucleus in;
4. The shielding provides more resistance to the extra repulsive forces felt by shielding;

Question 7

How do ionisation energies change doe G2?

Answer 7

1. Ionisation energies decrease down the group
   this is because electrons are further from the nucleus the more electron shells are added;
2. Therefore, there is less effective nuclear charge holding them in, and so the electrons are more easily booted out from the outer shells;
3. This means that ionisation energies decrease down the group, as less energy is needed to strip one mole of electrons from one mole of the element in a gaseous state;

Question 8

Why are the first and second ionisation energies lower than the third?

Answer 8

Because more energy is needed to strip electrons that are closer to the nucleus of an atom

Question 9

Give the reaction for G2 + Oxygen; what is special about this product?

Answer 9

1. They combust in Oxygen to produce metal oxides:
   G2 + Oxygen = Metal oxide;
2. Most of these oxides are alkalis, not bases - as they dissolve in water;
3. These metal oxides then go onto react with (dissolve in) water, to form strongly alkaline solution;

Question 10

Give the reaction for G2 + water

Answer 10

1. They react with water to produce metal hydroxides:
   Metal Hydroxide (2 lots of the OH), + Hydrogen, H2;
2. Most of these hydroxides are alkalis, not bases - as they dissolve in water;

Question 11

Give the reaction for G2 + dilute acid

Answer 11

They react with dilute acids to produce a salt and hydrogen:

G2 + acid = salt + hydrogen (H2)

Question 12

Name two uses for G2 compounds

Answer 12

1. Calcium Hydroxide (slaked lime), Ca(OH)2 is used in agriculture to neutralise acidic soils;
2. Magnesium Hydroxide, Mg(OH)2 and calcium carbonate CaCO3, are used in indigestion tablets as antacids;
   The neutralisation reaction for this is H+(aq) + OH-(aq)=H2O(l);

Question 13

How does the reactivity of G2 metal hydroxides change?

Answer 13

1. The oxides form more strongly alkaline solutions as you go down the group, because the hydroxides get more soluble;
2. This is because down the group, the less reactive the elements become, and so these bonds are more easily broken by the hydrogen bonds in water;

Question 14

What is a valuable exception when talking about the reactivity of G2 metal oxides?

Answer 14

Magnesium, and magnesium oxide - it is not as soluble as it should be following the trend, and reacts very slowly. This is because of its crystalline structure.