Group 1 Flashcards
Elements?
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
Properties?
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
How are lithium and sodium prepared?
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-
Preparation of potassium, rubidium and caesium?
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
Group 1 oxides?
All group 1 metals burn in air to form oxides but the main product of combustion depends on the metal
Lithium oxide?
Lithium burns to form lithium oxide, Li2O
4Li + O2 –> 2Li2O
Sodium oxide?
Sodium gives peroxide Na2O2
2Na + O2 –> Na2O2
Potassium oxide?
Potassium and heavier metal form superoxides
K + O2 –> KO2
Normal group 1 products of combustion?
Li2O, Na2O2, KO2, RbO2, CsO2 are normal products of combustion but all the metals can from an oxide, peroxide and superoxide under appropriate conditions
Oxides reacting with water?
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
Why does type of oxide by combustion change going down the group?
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
Why is sodium peroxide stale to heating but lithium peroxide doesn’t?
Using born Haber cycles to find lattice enthalpy the higher value of enthalpy for sodium leads to a higher decomposition temperature for sodium peroxide
Group 1 suboxides?
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
Group 1 metals reacting with water?
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
Density with water?
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