1.3.3 Group 2

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Group 2
Group 2 elements form 2+ ions. They all have 2 electrons in their outer shell, so they lose two to
form 2+ ions. Their ions then have the ultimate electron structure- that of a noble gas.
Reactivity increases down group 2. As you go down the group, the ionisation energies
decrease. This is due to the increasing atomic radius and shielding effect. When group 2
elements react react they lose electrons, forming positive ions. The easier it is to lose electrons
the more reactive the element, so reactivity increases down the group.
Group 2 elements react with water and oxygen. When group 2 elements react, they are oxidised
from a state of 0 to +2, forming M2+ ions. This is because group 2 atoms contain 2 electrons in
their outer shell.
They react with water to produce hydroxides- the group 2 metals react with water to give a
metal hydroxide and hydrogen e.g. M + 2H2O M(OH)2 + H2
They burn in oxygen to form oxides- when group 2 metals burn in oxygen, you get solid white
oxides e.g. 2M + O2 2MO
Group 2 oxides and hydroxides are bases. They form alkaline solutions in water. The oxides
of the group 2 metals react readily with water to form metal hydroxides, which dissolve. The
hydroxide ions, OH-, make these solutions strongly alkaline. Magnesium oxide is an exception-
it only reacts slowly and the hydroxide isn't very soluble. The oxides form more strongly alkaline
solutions as you go down the group, because the hydroxides get more soluble.
Thermal stability of carbonates changes down the group. Thermal decomposition is when a
substance breaks down when heated. The more thermally stable a substance is, the more heat
it will take to break down. Group 2 carbonates decompose to form the oxide and carbon dioxide
e.g. MCO3 MO + CO2. Thermal stability increase down the group. So it takes more heat to
decompose calcium carbonate than magnesium carbonate.
Group 2 compounds are used to neutralise acidity. They are known as the alkaline earth metals
and many of their common compounds are used for neutralising acids. Calcium hydroxide
(slaked lime) is used in agriculture to neutralise acid soil. Magnesium hydroxide is used in some
indigestion tablets as an antacid.

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