Q.Discuss the general characteristics and gradation in properties of alkaline earth metals.

General characteristics

• Outer electronic configuration ns$^2$; the two electrons are lost to give a stable, doubly-charged M$^{2+}$ ion — always +2 oxidation state.
• Harder, denser and with higher melting/boiling points than the corresponding alkali metals of the same period (stronger metallic bonding from two valence electrons).
• Smaller atomic and ionic radii than the alkali metal of the same period.
• Good conductors of heat and electricity; silvery-white lustre.

Gradation down the group (Be → Mg → Ca → Sr → Ba)

• Atomic/ionic radius: increases steadily.
• Ionisation enthalpy (both IE$_1$ and IE$_2$): decreases down the group (though always higher than the corresponding alkali metal), so reactivity increases down the group.
• Electropositive/metallic character increases down the group.
• Reaction with water: Be does not react, Mg reacts only with steam, Ca, Sr, Ba react readily even with cold water.
• Basicity of oxides/hydroxides increases down the group: BeO is amphoteric, MgO weakly basic, while CaO, SrO, BaO are strongly basic.
• Solubility of hydroxides increases down the group (Be(OH)$_2$ almost insoluble, Ba(OH)$_2$ fairly soluble), while solubility of carbonates and sulphates decreases down the group.
• Thermal stability of carbonates, nitrates and sulphates increases down the group as the cation's polarising power falls.
• Be, unlike the rest, forms largely covalent compounds due to its very small size and high polarising power (diagonal relationship with Al).

Split the answer into (a) features common to all alkaline earth metals — ns$^2$, +2 state, higher hardness/density/m.p. than Group 1 — and (b) the smooth gradation down the group in ionisation enthalpy, reactivity, basicity and solubility, noting Be's anomalous covalent behaviour.

• Describing alkaline earth metals as being as reactive as alkali metals, ignoring that IE and reactivity, while trending the same way down the group, are always lower/less than the corresponding alkali metal.
• Stating that all Group 2 hydroxides and carbonates follow the same solubility trend (hydroxide solubility rises down the group; carbonate/sulphate solubility falls — see Examples 4 and 5).
• Leaving out Be's distinct, largely covalent chemistry, which is a key part of the group's gradation.