Group II Flashcards
What is the trend in reducing power down group II?
Enaught value more negative down the group
Reducing power increases down the group
Because atomic radius increase down the group, ionisation energy decreases, tendency to be oxidised is INCREASED.
Group II ELEMENTS readily tarnish when they come into contact with air -> form metal oxide.
They are stored under l_____ p_______ with the exception of __ (protective oxide layer, tarnishes more slowly)
Liquid paraffin
Mg
Colour of metal oxides’ flame:
Mg is?
Brilliant white
Colour of metal oxides’ flame:
Ca is?
Brick red
Colour of metal oxides’ flame:
Sr is?
Crimson
Colour of metal oxides’ flame:
Ba is?
Apple green
Group II ELEMENTS react with water to give metal hydroxides M(OH)2 and H2 (g).
Resulting solution is ALKALINE.
Rxn of Mg and coldwater or mg with steam?
Mg reacts slowly with cold water
Mg(s) + 2H2O -> Mg(OH)2 (s) + H2 (g)
(White ppt) (weakly alkaline because mgoh2 sparingly soluble, not bc it is weak base)
Reacts readily with steam
Mg (s) + H2O (g) -> MgO(s) + H2 (g)
(White residue)
PH OF 8-10
Mg react with water pH?
8-10
Ca reacts readily with cold water
Give the reaction equation and pH of resulting solution?
Ca(s) + 2H2O (l) -> Ca(OH)2 (aq) + H2 (g)
pH 12-14
Note how the resulting metal hydroxide is SOLUBLE
Sr experiences VIGOROUS REACTION with cold water
Give the reaction equation and pH of resulting solution?
Sr (s) + 2H2O (l) -> Sr(OH)2 (aq) + H2 (g)
pH = 12-14
SOLUBLE METAL HYDROXIDE OK
Ba undergoes vigorous reaction with cold water
Give the reaction equation and pH of resulting solution?
Ba (s) + 2H2O -> Ba(OH)2 (aq) + H2 (g)
pH = 12-14
Oxides of group II metals, MO are generally:
1) w____
2) i____
3) b____
4) extremely high mp (they are ionic!!!)
exception: _____ is amphoteric
White
Ionic
Basic
BeO
Oxides of Group II elements react with water to form ???
MO (s) + H2O (l) -> M(OH)2 (aq)
Exception?
Hydroxides
BeO does not.
Why is reaction between MgO and water slow?
Very exothermic lattice energy YO
Mg has higher charge density compared to the rest down the group -> higher LE
Pattern of solubility of group II hydroxides down the group?
Increases down the group (think of LE decreasing down the group)
Mg(OH)2 is sparingly soluble, other hydroxides have appreciable solubilities, dissolve in water to give alkaline solutions
Thermal decomposition of nitrates, carbonates and hydroxides
Nitrates of group 2 elements M(NO3)2 thermally unstable, decompose to give _____?
simple metal oxide, nitrogen dioxide (brown gas) and oxygen.
M(NO3)2(s) -> MO (s) + 2NO2 (g) + (1/2)O2(g)
Thermal decomposition of carbonates and hydroxides are similar to that of nitrates. Equations?
MCO3(s) -> MO(s) + CO2 (g)
M(OH)2 (s) -> MO (s) + H2O (g)
Why are nitrates and carbonates prone to thermal decomposition?
Electron clouds of large anions more susceptible to polarisation.
Oxides more thermally stable than respective metal nitrates or carbonates. (Anion O2- is relatively smaller less polarisable)
Trend of thermal stability of nitrates down the group?
Increases down the group!
Radius of metal cation increases, charge density decreases. Ability of M2+ to polarise large NO32- anion decreases, N-O bonds weakened to smaller extent, so thermal stability of Group II nitrates increases down the group.
Why are group II elements good reducing agents?
Standard electrode potentials all highly negative aka they are easily oxidised.
What determines stability of carbonates nitrates down the group??
The key thing to rmb is how easily THE C,N,H are broken bc they are big anionic molecules, electron cloud easily distorted by cations (requires high charge density to polarise well and become covalent bond)
Down group, charge remains same but size increase, so charge density decreases.
Atomic radius of cation increase.
As charge density decrease -> polarizing power of cation decrease -> ease of distortion of electron cloud of NO3^- decrease, N-O bond less WEAKENED -> more energy required to break N-O bond -> stability increase
Why do metal oxides have high melting point?
Ionic bonds, large amount of energy required to overcome strong electrostatic attraction between M2+ and O2- ions.
BeO is actually c________ while other oxides of group 2 are ionic.
Hence it does not d_______ in water, is amphoteric, reacts with both _____________
Covalent
Dissolve
Acids and bases
Why is BeO covalent?
Be2+ has high charge density (top of the group) so it has high polarising power, distort electron cloud of O2- a lot, become covalent. Ionic with Covalent character stuff are usually amphoteric (like Al2O3)
Colour of group 2 metals down the group?
Brilliant white
Brick red
Crimson
Apple green
WRCG - where roland can’t go
