Group 2, the alkaline earth metals Flashcards
describe the physical appearance of the Group 2 metals in comparison to Group 1
harder and denser than the Group 1 metals
higher melting points, surface is covered in a layer of oxide
describe the trend in reactivity down the group
reactivity increases down the group
what is the trend of ionisation energy for group 2 elements ?
extra shells so more shielding so weaker attraction between the nucleus and the outer electrons - easier to remove the outer electrons so less energy needed
compare the sizes of a K+ ion and a Ca 2+ ion
Ca 2+ ion is smaller than a K + ion because the effective nuclear charge is 2 + compared to 1+ for K + so the remaining electrons are held more closely
what is the oxidation state of Group 2 metals in their compounds ?
+ 2
what types of agents is Group 2 metals ?
reducing agents
which metal in Group 2 is not a reducing agent ?
beryllium as they readily give up their two s electrons to form M 2+ ions
why is beryllium not a typical Group 2 element ?
the small size of its ion means that it has a much higher polarizing power than other Group 2 ions so its compounds have different chemical characteristics
what does group 2 elements produce in the reaction with oxygen ?
metal oxides - bases
group 2 oxides
- state the reaction of magnesium oxide and beryllium oxide
magnesium oxide - reacts very slowly and the hydroxide barely dissolves
beryllium oxide - does not react with water at all and the hydroxide is insoluble
as we go down the group, why do the group 2 oxides become more strongly alkaline ?
as the hydroxides become more soluble
how does oxides react with water ?
readily with water to make hydroxides which dissociate to form OH- ions
what does reaction with water for group 2 elements produce ?
metal hydroxides - bases
reactions with water - group 2 elements
- example
Sr (s) + 2H2O (l) -> Sr(OH) (aq) + H2 (g)
an increase of number of protons decreases down the group, what does the the shielding effect do ?
it overrides an increase in positive charge
Mg reacts slowly in cold water but more vigoursly in steam what does it produce ?
magnesium oxide instead of a hydroxide so the equation would be 2H2O(aq) not 2H2O(l)
what does group 2 elements produce when reacting with chlorine ?
metal chlorides - chlorides
reactions with chlorine - group 2 elements
- write the balanced equation for the reaction between beryllium and chlorine
Be (s) + CI2 (g) -> BeCI2 (s)
the oxides
- write the balanced symbol equation for the reaction between calcium oxide and nitric acid
CaO (s) + 2HNO3 (aq) -> Ca(NO3)2 (aq) + H2O (l)
the hydroxides - state the solubility
- magnesium hydroxides
- calcium hydroxide
- barium hydroxides
magnesium hydroxides - insoluble in water
calcium hydroxide - slightly soluble in water
barium hydroxides - the most soluble hydroxide
write the balanced equation for the thermal decomposition of calcium carbonate
CaCO3 (s) -> CaO (s) + CO2 (g)
describe the trend in thermal stability down the group
increases down the group
write the balanced symbol equation for the thermal decomposition of magnesium nitrate
2Mg(NO3)2 (s) -> MgO (s) + 4NO2 (g) + O2 (g)
describe the trend in thermal stability group 2
increases down the group
describe the trend in solubility in Group 2 sulfates down the group
- as the cation gets larger, it has a low charge stability
- it becomes less attracted to the polar water molecules
flame colors
metal ion
calcium
strontium
barium
calcium - brick red
strontium - crimson
barium - pale green
what is thermal stability ?
an indication of the ease with which compounds decompose on heating
polarizing power - define
indication of the extent to which a positive table is able to distort the electron cloud around a negative ions
explain why the thermal stability of carbonates and nitrates increases down the Group 2
- the carbonates ion becomes polarized
- as the positive ions get bigger as you go down the group, they have the less effect on carbonate ions near them
- to compensate for that, you heat the compound more in order to persuade the O2 to break free + leave the metal oxide
describe the type of ion with the greatest polarizing power in terms of charge and size
charge: large
size: small
neutralisation of group 2 oxides - example
CaO + 2HCI -> CaCI2 +H2O base + acid -> salt + water
neutralisation of group 2 hydroxides - example
Ca(OH)2 + 2HCI -> CaCI2 + 2H2O
base + acid -> salt + water
if the anion has a double charge how soluble is it as we go down the group ?
less
is the anion has a single charge how soluble is it as we go down the group ?
more soluble
what does carbonates break down into during thermal decomposition ?
metal oxides and carbon dioxide
what does nitrates break into during thermal decomposition ?
metal oxides, nitrogen dioxide and oxygen
write the balanced equation for the thermal decomposition of calcium nitrate
2Ca(NO3)2 (s) -> 2CaO (s) + 4NO2 (g) + O2 (g)
when the carbonate/ nitrate ion is nearby positive 2 metal ions what happens ?
it has a large electron cloud that can be distorted
explain why group 2 metal ions have a low charge density ?
they have a 2+ charge - they become larger as we go down the group meaning the charge is spread out over a larger area so low charge density
why is barium carbonate more stable than magnesium in the cloud in CO3 2- / NO3- ions ?
Mg 2+ is a smaller ion so it has a higher charge density and distorts the electron cloud more than Ba+ which has a lower charge density
the less distortion the more / less stable the carbonate is ?
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