The group 2 elements. Flashcards
What is the half life of radium?
1599 years.
What are the properties of the group 2 elements?
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.
Why is beryllium an exception to the group?
It forms a number of covalent compounds.
Why are they less reacted than may be expected?
There is coating of oxide on their surfaces.
How can magnesium be prepared?
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.
How can calcium be obtained?
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.
What are the equations involved in obtaining calcium?
CaCO3 –> CaO + CO2
6CaO + 2Al —> 3CaO . Al2O3 + 3Ca
What colour does magnesium burn with?
A bright white flame.
What happens to the reaction with burning the metals in air down the group, in terms of whether it is exothermic or endothermic?
It becomes more exothermic down the group.
What happens when the oxides are dissolved in water?
They form an alkaline solution of the hydroxides.
What was calcium oxide used for in the 1960s?
To provide a spotlight - limelight light burnt a mixture of oxygen and hydrogen.
What happens when the group 2 metals are reacted with oxygen?
They give the hydroxide and liberate hydrogen.
How does the rate of reaction change down the group with water?
It becomes more vigorous.
What happens when the hydroxides are heated?
They decompose to give the oxides.
What does amphoteric mean?
Can act as either a base or acid.
How do BeX2 compounds differ from the others in group 2?
They form polymeric structures with covalent bonds and bridging halides.
How does BeH2 differ from BeCl2?
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.
Why doesn’t MgCl exist?
It is unstable with respect to disproportionation, but stable with respect to the elements.
What are ethynides?
Compounds of group 2 metals and carbon - they contain the (C2)2- ion.
What is the equation for calcium ethynide reacting with water?
CaC2 + 2H2O –> Ca(OH)2 + C2H2.
What happens when the group 2 metals react with nitrogen?
They produce nitrides.
What is the equation for magnesium reacting with nitrogen?
3Mg + N2 —> Mg3N2.
What happens when the nitrides are added to water and write an equation.
They decompose to form the metal hydroxide and ammonia.
Mg3N2 + 6H2O —> 3Mg(OH)2 + 2NH3.
What happens when group 2 carbonates are heated?
They decompose to give the oxides and CO2.
