topic 4: inorganic chemistry and the periodic table

increases because one goes down the group, the atoms have more shells of electrons making the atom bigger

down the group the melting points decrease - the metallic bonding weakens as the atomic size increases - the distance between the positive ions and delocalized electrons increases - therefore the electrostatic attractive forces between the positive ions and the delocalized electrons weaken

the outermost electrons are held more weakly because they are successively further from the nucleus in additional shells. in addition, the outer shell electrons become more shielded from the attraction of the nucleus by the repulsive force of inner shell electrons

the reactivity increases down the group as the atomic radii increase - there is more shielding - the nuclear attraction decreases and it is easier to remove (outer) electrons and so cations form more easily - first ionisation energy decreases - there is a increase in repulsion between the filled inner shells and the electrons removed

the group 2 metals will burn in oxygen. Mg burns with a bright white flame 2Mg + O2 —> 2MgO MgO is a white solid with a high melting point due to its ionic bonding

The group 2 metals will react with chlorine Mg + Cl2 —> MgCl2

magnesium reacts in steam to produce magnesium oxide and hydrogen. the Mg would burn with a bright white flame Mg (s) + H2O (g)  MgO

giving a different magnesium hydroxide product Mg + 2 H2O  Mg(OH)2 + H2

react with cold water with increasing vigour down the group to form hydroxides Ca + 2H2O(l) —> Ca(OH)2(aq) + H2 (g) Sr + 2H2O(l)—> Sr(OH)2(aq) + H2(g) Ba + 2H2O(l) —> Ba(OH)2(aq) + H2(g)

MgO(s) + 2HCl(aq) —> MgCl2(aq) + H2O(l) SrO(s) + 2HCl(aq) —> SrCl2(aq) + H2O(l) CaO(s) + H2SO4(aq)  CaSO4(aq) + H2O(l)

2HNO3(aq) + Mg(OH)2(aq) —>Mg(NO3)2(aq) + 2H2O(l) 2HCl(aq) + Mg(OH)2(aq) —>MgCl2(aq) + 2H2O(l)

group II hydroxides become more soluble down the group. all Group II hydroxides when not soluble appear as white precipitates

insoluble in water

reasonably soluble in water

easily dissolve in water

group 2 sulfates become less soluble down the group

BaSO4

the use of heat to break down a reactant into more than one product

group 2 carbonates decompose on heating to produce group 2 oxides and carbon dioxide gas MgCO3(s) —> MgO(s) + CO2(g)

become more thermally stable going down the group. as the cations get bigger they have less of a polarising effect and distort the carbonate ion less. the C-O bond is weakened less so it less easily breaks down

group 1 carbonates do not decompose with the exception of lithium. as they only have +1 charges they don’t have a big enough charge density to polarise the carbonate ion. lithium is the exception because its ion is small enough to have a polarising effect Li2CO3(s) —> Li2O(s) + CO2(g)

one is to heat a known mass of carbonate in a side arm boiling tube and pass the gas produced through lime water. time for the first permanent cloudiness to appear in the limewater. repeat for different carbonates using the same moles of carbonate/same volume of limewater/same Bunsen flame and height of tube above flame

group 2 nitrates decompose on heating to produce group 2 oxides, oxygen and nitrogen dioxide gas. you would observe brown gas evolving (NO2) and the white nitrate solid is seen to melt to a colourless solution and then re-solidify 2Mg(NO3)2 → 2MgO + 4NO2 + O2

decreases