group 2 Flashcards
atomic radius down the group
atomic radius decrease down the group
as one goes down the group, the atoms have more shells of electrons making the atom bigger
melting points down the group
decreases, the metallic bonding weakens as the atomic size increases. the distance between the positive ions and the delocalised electrons increases. therefore the electrostatic attractive forces between the positive ions and the delocalised electrons weaken
1st ionisation energy down the group
decreases, 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 the inner shell electrons
reactivity down the group
increases down the group as the atomic radii increase, there is more shielding. the nuclear attraction decreases and it is easier to remove the outer electrons and so cations form more easily
group 2 reactions with oxygen
will burn in oxygen to form metal oxides
e.g. 2Mg + O2 = 2MgO
what will 2Mg + O2 form?
bright white flame
MgO is a white solid with a high melting point due to it’s ionic bonding
what do you use to clean off Mg ribbon?
emery paper
why does the Mg ribbon need to be cleaned before doing reactions with it?
it will have a thin layer of magnesium oxide on it formed by reaction with oxygen
if testing for reaction rates with Mg and acid, an un-cleaned Mg ribbon would give false result because both the Mg and MgO would react at different rates
group 2 reactions with chlorine
form a metal chloride
e.g. Mg + Cl2 = MgCl2
group 2 reactions with cold water
produces hydroxide and hydrogen
e.g Ca + 2H2O (l) = Ca(OH)2 (aq) + H2 (g)
what would you observe when reacting group 2 metals with water?
- fizzing (more vigorous down group)
- metal dissolving (faster down group)
- solution heating up (more down group)
- calcium - white precipitate appearing (less precipitate down group)
magnesium reaction with steam
Mg (s) + H2O (g) = MgO (s) + H2 (g)
- the magnesium would burn with a bright flame
magnesium reaction with warm water
Mg + 2H2O = Mg(OH)2 + H2
- much slower reaction than the reaction with steam and there is no flame
ionic group 2 oxides with water
produce hydroxide ions
e.g. Ca (s) + H2O (l) = Ca(OH)2 (aq)
magnesium oxide reacting with water
MgO (s) + H2O (l) = Mg(OH)2 (s)
- only slightly soluble in water so fewer free OH- ions are produced and so lower pH
group 2 oxides reacting with acids
produces metal chloride/sulfate/nitrate + H2O
e.g. MgO (s) + 2HCl (aq) = MgCl2 (aq) + H2O (l)
CaO (s) + H2SO4 (aq) = CaSO4 (aq) + H2O (l)
group 2 hydroxides reacting with acids
produces metal chloride/sulfate/nitrate + H2O
e.g. 2HNO3 (aq) + Mg(OH)2 (aq) = Mg(NO3)2 (aq) + 2H2O(l)
2HCl (aq) + Mg(OH)2 (aq) = MgCl2 (aq) +2H2O
solutbility of hydroxides group 2
more soluble down the group - all group 2 hydroxides when not soluble appear as white precipitates
is Mg(OH)2 insoluble or soluble in water + simplest ionic equation for formation of Mg(OH)2?
insoluble
Mg2+ (aq) + 2OH- (aq) = Mg(OH)2 (s)
solubility of sulfates in group 2
less soluble down the group Ba SO4 is the least soluble
thermal decomposition
use of heat to break down a reactant into more than one product
ease of thermal decomposition in group 2 elements
decreases down the group
why do group 2 carbonates become more thermally stable down the group?
the cations get bigger, they have less of a polarising affect and distort the carbonate ion less. the C-O bond is weakened less so it less easily breaks down
what do group 2 carbonates produce when decomposed
metal oxide and carbon dioxide e.g. MgCO3 (s) = MgO (s) + CO2 (g)
why don’t group 1 carbonates decompose (with the exception of lithium)
they only have 1+ charges, they don’t have a big enough charge to polarise the carbonate ion. Li is the exception because its ion is small enough to have a polarising effect
what do group 2 nitrates decompose to form?
2 oxides, oxygen, nitrogen dioxide gas
e.g. 2Mg(NO3)2 = 2MgO + 4NO2 + O2
what would you observe when nitrates decompose
brown gas and the white nitrate solid is seen to melt to a colourless solution then re-solidify
why does magnesium nitrate decompose the easiest
Mg2+ ion is the smallest and has a greater charge density. it causes more polarisation of the ntrate anion and weakens the N-O bond
how do group 1 nitrates decompose?
form nitrate (III) salt and oxygen
e.g. 2NaNO3 = 2NaNO2 + O2
