The group 2 elements.

Question 1

What is the half life of radium?

Answer 1

1599 years.

Question 2

What are the properties of the group 2 elements?

Answer 2

They are metallic solids at room temperature and pressure, they have higher melting points, boiling points and enthalpy changes of atomisation than their group 1 neighbours due to stronger metallic bonding due to the presence of two valence electrons per atom.

Question 3

Why is beryllium an exception to the group?

Answer 3

It forms a number of covalent compounds.

Question 4

Why are they less reacted than may be expected?

Answer 4

There is coating of oxide on their surfaces.

Question 5

How can magnesium be prepared?

Answer 5

It is obtained from sea water - calcium hydroxide solution is added causing Mg(OH)2 to precipitate. This is then treated with HCl to produce MgCL2 and the metal can then be liberated using electrolysis.

Question 6

How can calcium be obtained?

Answer 6

Minerals such as limestone. The carbonate in the limestone is converted into the oxide by heating (900-1100 degrees) and then the metal is obtained from the reduction of CaO with aluminium.

Question 7

What are the equations involved in obtaining calcium?

Answer 7

CaCO3 –> CaO + CO2

6CaO + 2Al —> 3CaO . Al2O3 + 3Ca

Question 8

What colour does magnesium burn with?

Answer 8

A bright white flame.

Question 9

What happens to the reaction with burning the metals in air down the group, in terms of whether it is exothermic or endothermic?

Answer 9

It becomes more exothermic down the group.

Question 10

What happens when the oxides are dissolved in water?

Answer 10

They form an alkaline solution of the hydroxides.

Question 11

What was calcium oxide used for in the 1960s?

Answer 11

To provide a spotlight - limelight light burnt a mixture of oxygen and hydrogen.

Question 12

What happens when the group 2 metals are reacted with oxygen?

Answer 12

They give the hydroxide and liberate hydrogen.

Question 13

How does the rate of reaction change down the group with water?

Answer 13

It becomes more vigorous.

Question 14

What happens when the hydroxides are heated?

Answer 14

They decompose to give the oxides.

Question 15

What does amphoteric mean?

Answer 15

Can act as either a base or acid.

Question 16

How do BeX2 compounds differ from the others in group 2?

Answer 16

They form polymeric structures with covalent bonds and bridging halides.

Question 17

How does BeH2 differ from BeCl2?

Answer 17

BeH2 is electron deficient and the Be-H-Be bridges involve 3-centre 2-electron bonding, whereas BeCL2 is not electron deficient because the bridging chloride donates three electrons.

Question 18

Why doesn’t MgCl exist?

Answer 18

It is unstable with respect to disproportionation, but stable with respect to the elements.

Question 19

What are ethynides?

Answer 19

Compounds of group 2 metals and carbon - they contain the (C2)2- ion.

Question 20

What is the equation for calcium ethynide reacting with water?

Answer 20

CaC2 + 2H2O –> Ca(OH)2 + C2H2.

Question 21

What happens when the group 2 metals react with nitrogen?

Answer 21

They produce nitrides.

Question 22

What is the equation for magnesium reacting with nitrogen?

Answer 22

3Mg + N2 —> Mg3N2.

Question 23

What happens when the nitrides are added to water and write an equation.

Answer 23

They decompose to form the metal hydroxide and ammonia.

Mg3N2 + 6H2O —> 3Mg(OH)2 + 2NH3.

Question 24

What happens when group 2 carbonates are heated?

Answer 24

They decompose to give the oxides and CO2.

Question 25

What happens to the decomposition temperature of the carbonates down the group?

Answer 25

It increases.

Question 26

What is decomposition temperature related to?

Answer 26

The temperature at which the reaction becomes spontaneous - when deltarG becomes negative.

Question 27

What is the change in the Gibbs equation for the carbonates mostly dependent on?

Answer 27

As entropy is largely independent of the group 2 element it is mostly dependent on differences between the lattice enthalpies of the reactants and products.

Question 28

What do group 2 nitrates and sulfates decompose to give?

Answer 28

The oxides. (and NO and O2 for the nitrates and SO3 for the sulfates).

Question 29

What is limestone used for?

Answer 29

A building material.

Question 30

What happens when limestone is heated?

Answer 30

It loses CO2 to form CaO (quicklime).

Question 31

What is a typical component of cement?

Answer 31

Ca3SiO5.

Question 32

What is Portland cement?

Answer 32

Gypsum, tricalcium silicate.

Question 33

Why are group 2 elements less soluble than group 1?

Answer 33

They have higher lattice enthalpies.

Question 34

What is barium sulfate used in?

Answer 34

X-ray contrast agent in images of the digestive tract.

Question 35

Why is the coordination chemistry of group 2 more extensive than group 1?

Answer 35

The ions are smaller and have twice the charge.

Question 36

How does coordination typically change down the group 2 elements?

Answer 36

It increases due to the increasing size of the ions.

Question 37

What dictates the nature of the complex formed with aqua ligands?

Answer 37

The size of the ions.

Question 38

What does the high charge density of Be2+ result in?

Answer 38

Hydrolysis so solutions of Be2+ are acidic.

Question 39

What are chlorophylls?

Answer 39

Pigment molecules that give leaves their green colour.

Question 40

What are chlorophylls made up of?

Answer 40

They are magnesium coordination complexes that contain Mg2+ ions lying in the centre of a chlorin ring.

Question 41

What is strange about beryllium in contrast to other group 1 elements?

Answer 41

It does not react with water, it is amphoteric, compounds of beryllium have much greater covalent character, it is acidic in aqueous solution, and BeO does not react with water unlike other oxides.

Question 42

Why are these unusual properties of beryllium observed?

Answer 42

There is a high charge density on Be2+ which makes the lattice enthalpies of compounds very high. It also means the free ion is strongly polarising and draws the electrons of neighbouring ions towards itself, giving its bonds a much higher covalent character.