Chemical Ideas 11.2
The s block: Groups 1 & 2
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The s block: Groups 1 & 2
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The s block contains two groups of reactive
metals.
Group 1 metals (alkali metals)
Group 2 metals (alkali earth metals)
Elements become more metallic as you go down
a group – for this reason most reactive metals
are found at the bottom of the groups
Elements become less metallic as you go across
a period from left to right – for this reason Gp
1 metals are more reactive than Gp 2 metals in
the same period
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Department
Physical properties
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S block are only really typical metals in there
chemical properties
Metals are not widely used in element form as the
more familiar d – block metals
Tend to be
 Soft
 Weak
 Low melting points
 Too reactive with water and oxygen to have many
uses
 Compounds of s-block elements are very important
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Department
Chemical reactions
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Group 1 & 2 metals are all v. reactive
Never found in nature in there native,
uncombined state
Compounds of s block metals are very
common throughout nature
A lot of the ground beneath our feet in
made from compounds of Ca and Mg!
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Department
Chemical reactions
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Group 1 & 2 show patterns of reactivity as you go
down the group
There are similarities between the reaction of
the elements in the group, also differences these
difference show up in patterns or trends
The similarities are because elements in the same
group have the same number of e’s in the outer
shell
Difference’s are because as you go down a group
the size of the atom increases.
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Department
Some chemical properties of Group 2
elements and their compounds
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Magnesium, calcium, Strontium and Barium
are most well known
Elements are all reactive
Form compounds containing ions with a +2
charge such as Mg2+ and Ca2+
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Reactions of group 2 elements
with water
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All react with water to form hydroxides and
hydrogen
Steady increase in reactivity as you go down
group
Mg reacts slowly even when water is heated
Ba reacts rapidly
None react as vigorously as Gp 1 metals
General equation:
M(s) + 2H20 (l)  M(OH)2 (aq) + H2 (g)
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Oxides and hydroxides
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General formula of the oxides is MO
General formula of the hydroxides is M(OH)2
In water, oxides and hydroxides form alkaline solutions
(although not very soluble)
Typical of metals, unlike non-metals whose oxides form acidic
solutions
Strongest alkaline solutions are formed by elements at bottom
of group
Oxides and hydroxides react with acids to form salts
MO (s) + 2HCl (aq)  MCl2 (aq) + H20 (l)
M(OH)2 (s) + H2SO4(aq)  MSO 4(aq) + 2H20 (l)
This neutralising effect is used by farmers when they put
lime (calcium hydroxide) on their fields to neutralise soil
acidity
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Department
Effect of heating carbonates
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The general formula of Gp 2 carbonates is MCO3
Heating carbonates makes them decompose, forming the oxide
and releasing carbon dioxide
MCO3 (s)  MO (s) +CO 2(g)
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Carbonates more difficult to decompose the further you go
down the group
We say the thermal stability of calcium carbonate is greater
than that of magnesium carbonate
Decomposition of calcium carbonate (limestone) is an important
process used to manufacture calcium oxide (quicklime)
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Department
Solubility of compounds
Solubility of hydroxides
 More soluble as you go down the group
 Pattern is repeated for most Gp 2 compounds
where the negative ion has a single charge (1-)
Solubility of carbonates
 Less soluble as you go down the group
 Pattern is repeated for most Gp 2 compounds
where the negative ion has a double charge (2-)
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Department
Solubility of compounds
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Numbers in table don’t
show a perfect trend
This rule is generally
correct but and is useful
in making predictions
As in all science the
predictions can’t be
confirmed until you or
someone else confirms it
through experiments
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Department