Group 1

Question 1

Elements?

Answer 1

First five are metallic solids at room temperature and pressure, the melting point of caesium is low enough for it to melt in hot weather. Francium is radioactive and has not been isolated as the pure element. Chemistry of these elements dominated by +1 oxidation state

Question 2

Properties?

Answer 2

Low melting points, boiling points and enthalpy of atomisation reflect relatively weak metallic bonding, low densities due to large atomic radii and relatively open body cubic structures

Question 3

How are lithium and sodium prepared?

Answer 3

Industrially via electrolysis of their molten chlorides.
For sodium in a Downs cell, CaCl2 used to reduce melting point
Reduction at cathode: 2Na+ + 2e- –> 2Na
Oxidation at anode: 2Cl- –> Cl2 + 2e-

Question 4

Preparation of potassium, rubidium and caesium?

Answer 4

Prepared by the reduction of their molten salts with sodium at high temperatures
KCl + Na —> K + NaCl
potassium is more reducing than sodium so the equilibrium lies to the left hand side, the more volatile potassium is obtained by fractional distillation which displaces the equilibrium to the right hand side

Question 5

Group 1 oxides?

Answer 5

All group 1 metals burn in air to form oxides but the main product of combustion depends on the metal

Question 6

Lithium oxide?

Answer 6

Lithium burns to form lithium oxide, Li2O

4Li + O2 –> 2Li2O

Question 7

Sodium oxide?

Answer 7

Sodium gives peroxide Na2O2

2Na + O2 –> Na2O2

Question 8

Potassium oxide?

Answer 8

Potassium and heavier metal form superoxides

K + O2 –> KO2

Question 9

Normal group 1 products of combustion?

Answer 9

Li2O, Na2O2, KO2, RbO2, CsO2 are normal products of combustion but all the metals can from an oxide, peroxide and superoxide under appropriate conditions

Question 10

Oxides reacting with water?

Answer 10

All group 1 oxides are basic and great with water to give hydroxides
Li2O + H2O –> 2LiOH
Na2O2 + 2H2O –> 2NaOH + H2O2
5KO2 + 2H2O –> 4KOH + 3O2

The reaction with KO2 is used in submarine breathing system to generate O2 and the OH products absorbs CO2

Question 11

Why does type of oxide by combustion change going down the group?

Answer 11

As a general rule large anions are stabilised by large cations, the ionic radius of group 1 cations increases down the group and the larger cations are better at stabilising the large peroxide and superoxide ions with respect to decomposition into oxide and oxygen gas

Question 12

Why is sodium peroxide stale to heating but lithium peroxide doesn’t?

Answer 12

Using born Haber cycles to find lattice enthalpy the higher value of enthalpy for sodium leads to a higher decomposition temperature for sodium peroxide

Question 13

Group 1 suboxides?

Answer 13

Rubidium and caesium burn in limited amounts of oxygen to form a class of intensely coloured compounds called suboxides an example includes Rb9O2, although the metal oxidation state in a suboxide appears to be less than +1 this is not really the case. The additional electrons are actually delocalised over the whole structure these delocalised electrons electrons give rise to metallic behaviour

Question 14

Group 1 metals reacting with water?

Answer 14

All react with water to give hydroxide and hydrogen gas
2Na + H2O –> 2NaOH + H2
These reactions are very exothermic and the violence of the reactions increases going down the group

Question 15

Density with water?

Answer 15

Lithium, sodium and potassium are all less dense than water so they react on the surface with the exception of lithium the reactions are exothermic enough to melt the metals and the reaction with potassium is sufficiently vigorous to ignite the hydrogen produced. Rubidium and caesium are denser than water so they sink beneath the surface and react explosively

Question 16

How is sodium hydroxide prepared industrially?

Answer 16

By the electrolysis of sodium chloride solution known as the chloroalkali process
2NaCl + 2H2O –> 2NaOH + H2 + Cl2

Question 17

Group 1 halides?

Answer 17

Colourless and ionic solids with high melting points. Sodium chloride is obtained either by mining naturally occurring deposits or by the evaporation of sea water

Question 18

Group 1 ethynides?

Answer 18

Group 1 metals all react with ethyne in liquid ammonia to form ethynides which contain the HC2- mono anion or the C22- dianion
2Li + 2HC—CH —> 2Li+C—CH- + H2
2Li + HC—CH —> (Li+)2C—C2- + H2

Group 1 ethynides decompose in water to form LiOH with ethyne
Li2C2 + 2H2O —> 2LiOH + C2H2

Question 19

Group 1 Nitrides?

Answer 19

Lithium is the only group 1 metal to form a stable binary nitride. Lithium nitride is prepared from the reaction of lithium with nitrogen at high temperature and pressure
6Li + N2 —> 2Li3N
Lithium nitride decomposes in water to form lithium hydroxide and ammonia
Li2N + 3H2O —> 3LiOH + NH3
Lithium nitride shows high Li+ ion conductivity and is being investigated for use in Li-ion batteries

Question 20

Compounds with oxyanions?

Answer 20

The group 1 metals form salts with oxyanions such as nitrates, carbonates and sulphates. Most group 1 nitrates MNO3 decompose on heating to the nitrites MNO2
2MNO3 —> 2MNO2 + O2
though for lithium decomposing gives the oxide
4LiNO3 –> 2Li2O + 4NO + 3O2

Question 21

Nitrates stability?

Answer 21

Nitrates become more stable with respect to decomposition as the group is descended the increasing stability of the nitrates down group 1 is largely due to the decrease in the difference in lattice enthalpies of the nitrate and nitrite which makes decomposition less favoured

Question 22

Small anions stability?

Answer 22

Compounds with small anions becomes less stable down the group this is mainly due to the decrease in the lattice enthalpy of these compounds as the group is descended. When these compounds decompose on heating they decompose to the elements

Question 23

Large anions stability?

Answer 23

Compounds with large anions become more stable down the group this is due to the decrease in the lattice enthalpies of the decompositions products

Question 24

Solubility of group 1 compounds?

Answer 24

Most group 1 salts are soluble in water for last containing large anions such as chlorides, bromides and iodides and nitrates, the solubility generally decreases down the group and the lithium salts are the most stable.
For salts with small anions such as fluorides and hydroxides the solubility increases down the group and the rubidium and caesium salts are the most soluble

Question 25

What does whether a compound is soluble depend on?

Answer 25

The relative magnitudes of the lattice Gibbs energy and the Gibbs energy of hydration of the ion, we have to use Gibbs emerges rather than enthalpies since entropies cannot be ignored

Question 26

When is a compound soluble?

Answer 26

If deltasolG is negative, both lattice Gibbs energy and Gibbs energy changes of hydration are large but with opposite signs this means deltasolG is small which is why entropies cannot be ignored Generally compounds with large cations and small anions, or small cations and large anions are soluble

Question 27

Group 1 Coordination Chemistry?

Answer 27

Metals ions are lewis acids and so they are able to interact with Lewis bases, this is the basis of coordination chemistry where the bases are called ligands. The group 1 ions are singly charged and relatively large so they have low charge density as a results they are weak Lewis acids and unlike many other metals they coordinate only very weakly to simple ligands such as water. The coordination becomes weaker down the group as the charge density on the cation decreases

Question 28

What coordination complexes do group 1 form?

Answer 28

Crown ethers, relationships between cavity size, cationic radius and stability of the resulting complex, known as optimal spatial fit. Another type of ligands that binds to group 1 cations is the cryptands, from more stable complexes than crown ethers as less rearrangement of the ligand is added to coordinate to the cation. Like crown ethers cryptands are size selective and they form the most stable complexes with cations that fit best into the central cavity

Question 29

Reaction with liquid ammonia?

Answer 29

All group 1 metals dissolve in liquid ammonia to give dark blue solutions, unlike the reaction of sodium with water the solvent is not being reduced instead the metal atoms ionise into cations and electrons both of which are solvated by the liquid ammonia Na ---> Na+ + e-

Question 30

Why does the solution of liquid ammonia turn blue?

Answer 30

The colour of the solution is independent of the metal used and is due to the solvated electrons. These electrons sit in cavities formed by groups of NH3 molecules. The solvated electrons act like free electrons and so the solutions are strong reducing agents

Question 31

Examples of group 1 being reduced by liquid ammonia

Answer 31

C60 is reduced to [C60]3- anion on reaction with rubidium in liquid ammonia C60 + 3Rb+ 3e- --> Rb3[C60] The nickel (II) complex [Ni(CN)4]4- is reduced to nickel (0) complex by sodium in liquid ammonia [Ni(CN)4]2- + 2Na+ + 2e- --> [Ni(CN)4]4- At high concentrations of the metal the blue colour turns into a metallic bronze and the liquid ammonia solution begins to conduct electricity, the electrons are delocalised throughout the solution in a similar manner to the delocalisation of electrons in a solid metal.

Question 32

Solvated electron solution unstable?

Answer 32

The solvated electron solutions are thermodynamically unstable and after several days ammonia is reduced to form sodium amide and hydrogen 2Na + 2NH3 --> 2NaNH2 + H2