Group IIA Elements:
Beryllium (Atomic number – 4)
Magnesium (Atomic number – 12)
Calcium (Atomic number – 20)
Strontium (Atomic number – 38)
Barium (Atomic number – 56)
Radium (Atomic number – 88)
- Have 2 electrons in the outermost orbit.
- By loosing two electrons they form stable + 2 ions.
- They are divalent and show + 2 as the stable oxidation state.
General trends in Periodic Table:
- As we move from top to bottom, atomic radius increases.
- Order of atomic radius: Be < Mg < Ca < Sr < Ba < Ra
- Ionization potential decreases down the group.
- Density increases with increase in atomic mass.
- Electronegativity decreases from top to bottom.
- Stability of thermal decomposition of metal carbonates increases down the group.
- Solubility of carbonates in water decreases down the group.
- Hydration enthalpy decreases down the group.
- Reactivity towards Halogens
All the alkaline earth metals combine with halogen forming their halides.
M + X₂ → M X₂ (X = F, Cl, Br, I)
Flame Test: Be and Mg give negative flame test as the electrons are strongly bound.
Hydration Enthalpy: Like alkali metals ions, the hydration enthalpies of alkaline earth metals ion decrease with increase in ionic size down the group.
General characteristics of compounds of alkaline earth metals:-
1. Oxides and Hydroxides: The alkaline earth metals burn in oxygen to form monoxide of the form MO. BeO is Amphoteric and rest are ionic in nature.
MO + H₂O → M (OH)₂ (hydroxide)
The solubility, thermal stability and the basic character of hydroxides increases with increase in atomic number.
2. Halides: Except for Beryllium halides, all halides of alkaline earth metals are ionic in nature.
3. Salts of Oxoacids:
- Carbonates of alkaline earth metals are insoluble in water.
- Metal carbonates on heating give metal oxide and carbon dioxide gas on heating.
- Beryllium carbonate in highly unstable hence are kept in CO₂ atmosphere.
MCO₃ (s) → MO (s) + CO₂ (g).
- On heating give metal oxides and Nitrogen dioxide.
- Tendency of formation of hydration decreases with increase in size.
M (NO₃)₂ (s) → 2MO (s) + 4NO₂ (g) + O₂ (g).