Group 2 Reactions
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36. Group 2
Melting points
Down the group the melting points decrease. The
Atomic radius
metallic bonding weakens as the atomic size
Atomic radius increases down the Group.
increases. The distance between the positive ions and
As one goes down the group, the atoms have more
delocalized electrons increases. Therefore the
shells of electrons making the atom bigger.
electrostatic attractive forces between the positive
ions and the delocalized electrons weaken.
1st ionisation energy
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
Group 2 reactions
Reactivity of group 2 metals increases down the group
Reactions with oxygen.
Mg will also react slowly with oxygen without a flame.
The group 2 metals will burn in oxygen.
Mg ribbon will often have a thin layer of magnesium oxide on it
Mg burns with a bright white flame.
formed by reaction with oxygen.
2Mg + O
2MgO
2Mg + O
2MgO
2
2
This needs to be cleaned off by emery paper before doing
MgO is a white solid with a high melting
reactions with Mg ribbon.
point due to its ionic bonding.
If testing for reaction rates with Mg and acid, an un-cleaned Mg
ribbon would give a false result because both the Mg and MgO
would react but at different rates.
Mg + 2HCl
MgCl
+ H
2
2
MgO + 2HCl
MgCl
+ H
O
2
2
Reactions with water
.
Mg will also react with warm water, giving a different
Magnesium burns in steam to produce
magnesium hydroxide product.
magnesium oxide and hydrogen. The Mg
would burn with a bright white flame.
Mg + 2 H
O
Mg(OH)
+ H
2
2
2
Mg (s) + H
O (g)
MgO (s) + H
(g)
This is a much slower reaction than the reaction with
2
2
steam and there is no flame.
Make sure you learn the difference between the reaction of
Magnesium with steam and that of warm water
The hydroxides produced make the water alkaline
(if they are soluble in water)
The other group 2 metals will react with cold water with
One would observe:
increasing vigour down the group to form hydroxides.
•fizzing, (more vigorous down group)
Ca + 2 H
O (l)
Ca(OH)
(aq) + H
(g)
2
2
2
•the metal dissolving, (faster down group)
Sr + 2 H
O (l)
Sr(OH)
(aq) + H
(g)
2
2
2
•the solution heating up (more down group)
Ba + 2 H
O (l)
Ba(OH)
(aq) + H
(g)
2
2
2
•and with calcium a white precipitate
appearing (less precipitate forms down
group)
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