Group 2 Elements

The table shows the decomposition temperature of the carbonates of Group 2 elements.

Why is BeCO₃ unstable thermally?

• The electron cloud of the Be²⁺ ion is polarised by the CO₃^2– ion.

• The electron cloud of the CO₃^2– ion is polarised by the Be²⁺ ion.

• Going down Group 2, the size of the cation increases and the polarisation of the anion by the cation becomes greater.

• A small cation absorbs energy more efficiently and can be excited to a higher energy level which is unstable.

Magnesium is a Group 2 element. When magnesium carbonate is heated, magnesium oxide is formed and carbon dioxide is liberated.

MgCO₃ --> MgO + CO₂

Which of the following is true when going down the group?

• Lattice energy of carbonates decreases

  Lattice energy of oxides decreases

  Thermal stabilities of oxide decreases

• Lattice energy of carbonates decreases

  Lattice energy of oxides decreases

  Thermal stabilities of oxide increases

• Lattice energy of carbonates increases

  Lattice energy of oxides increases

  Thermal stabilities of oxide decreases

• Lattice energy of carbonates decreases

  Lattice energy of oxides increases

  Thermal stabilities of oxide decreases

Beryllium is a Group 2 element. Which of the following is the anomalous properties of beryllium?

• Beryllium oxide is amphoteric

• Beryllium chloride does not dissolve in water

• Beryllium forms a covalent compound with fluorine

• Beryllium oxide can form dimer.

Aqueous beryllium chloride has a pH less than 7 because

• the charge density of the beryllium ion is high

• the beryllium ion undergoes hydrolysis

• beryllium chloride undergoes partial dissociation in water

• beryllium chloride is a covalent compound

The solubilities of the sulphates of Group 2 metals decrease down the group because

• the cation size increases from Mg²⁺ to Ba²⁺

• the hydration energy of the cations becomes less exothermic from Mg²⁺ to Ba²⁺

• the sulphates ion very much smaller than these cations.

The carbonates, nitrates and hydroxides of Group 2 elements decompose to their respective oxides when heated. Hence, it can be concluded that

• all compounds of Group 2 elements are unstable to heat

• Group 2 elements are strong reducing agents

• the oxide is energetically more stable than the carbonates, nitrates and hydroxides

• the metallic properties of the elements increases down the Group

Barium sulphate, BaSO₄ is less soluble than magnesium sulphate, MgSO₄. This is because

• BaSO₄ is covalent whereas MgSO₄ is ionic

• the lattice energy of BaSO₄ is higher than that of MgSO₄

• the hydration energy of Ba²⁺ is less than than of Mg²⁺

• the enthalpy of solution of BaSO₄ is more exothermic than that of MgSO₄

The metals of Group 2 react readily with oxygen to form compounds of general formula MO. When each of these oxides is added to water, which forms the most alkaline ?

• MgO

• CaO

• SrO

• BaO

Steam is passed over heated magnesium to give compound X and hydrogen.

what is not the property of Compound X ?

• It has a high melting point

• It is a basic oxide

• It is a white solid

• It is very soluble in water

Which statement about the oxides and hydroxides of the Group 2 elements Mg, Ca, Sr and Ba is correct ?

• Each of the oxides reacts readily with water to form pH 12 or above

• Magnesium oxide is used as a furnace lining because it has giant molecular structure and hence a high melting point

• The hydroxides are produced directly by the thermal decomposition of the corresponding nitrates

• The solubility of hydroxides increases from Mg to Ba