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Group 2 Alkaline earth metals
The elements of group II are known as the alkali earth metals.
All of these elements are reactive metals. Magnesium and calcium are abundant in the earth's crust. The
others are relatively rare.
The physical properties of the elements
Melting points and electrical conductivity:
The melting points of the elements decrease down group II.
Down the group, the size of the cations increases and the charge on the cations remains constant. The
charge density thus decreases and the attraction between the cations and the delocalized electrons
also decreases. The melting points and hardness therefore decrease.
All group II elements will conduct electricity because the delocalized electrons are free to move
throughout the solid.
First & second ionization energies:
The first & second ionization energies decrease down group II.
Down the group, the number of shells increases. Therefore the outer shells are more shielded from the
nucleus, the effective nuclear charge decreases , are less closely held and are easier to remove.
Successive ionization energies.
The second ionization energy of group 2 elements is higher than the first as the second electron is
removed from an already positive ion. There is greater attraction to as the effective nuclear charge
attracting the outer electron has increased.
The third ionisation energy of group 2 elements is much higher(there is a jump) than the second. The
third electron must be removed from a doubly positively charged ion and from a stable full energy level
closer to the nucleus.
Group 2 Element configuration I.E.s
in kJ Third
Mg 12 [Ne] 3s2 736 1450 7733
Ca 20 [Ar] 4s2 590 1150 4912
Sr 38 [Kr] 5s2 548 1060 4210
Ba 56 [Xe] 6s2 502 966
Reactions of group 2 elements
(a) Reactions with oxygen
Group 2 elements form the solid ionic oxide of formula MO when heated in oxygen.
For example magnesium forms magnesium oxide
2Mg(s) + O2(g) 2MgO(s)
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Reactions with chlorine
All the group 2 metals react when heated in chlorine to form solid ionic chlorides.
Magnesium for example:
Mg(s) + Cl2(g) MgCl2(s)
(c) Reactions with water
Be does not react with water or steam.
Magnesium burns when heated in steam to form magnesium oxide and hydrogen.
Mg (s) + H2O(g) MgO (s) + H2(g)
Calcium reacts steadily with cold water.…read more

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Ba2+(aq) + SO42(aq) BaSO4(s) thick white precipitate formed
Sr2+(aq) + SO42(aq) SrSO4(s) thick white precipitate formed
Ca2+(aq) + SO42(aq) CaSO4(s) faint white precipitate formed
If dilute sulphuric acid or sodium sulphate is added to a solution of Mg2+ or Be2+, there is no reaction
and no precipitate is formed.…read more

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The decomposition is a result of the polarising power of the cation.
As polarising power of the cation increases, compounds become more covalent in character and less
stable to heat.
Going down the group the cations become larger charge remains the same , so their polaring power
The smallest ion, Mg2+, has the highest charge density (is the most polarising), and forms the
compound with the small anion most readily (i.e. at the lowest temperature).…read more


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