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The Group 2S Block Elements

Group 2 of the periodic table is composed of the alkaline-earth metals beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). Their physical properties are recorded in Table.

Table: General Physical Properties of Alkaline Earth Metals

Property Be Mg Ca Sr Ba Ra
Electronic configuration [He]2s2  [Ne]3s2  [Ar]4s2  [Kr]5s2  [Xe]6s2  [Rn]7s2
Atomic number 4 12 20 38 56 88
Relative atomic mass 9.012   24.305 40.08 87.67 137.33 226.025

Abundance in earth's crust (ppm) 

2 27640 46668 384 390 10-6

Atomic radius, r/pm

112 160 197 215 222

Ionic radius for 6-coordinate, r/pm

27*  72 100 118 135 148

Melting point, T/K

1580 922 1112 1041 1000 (973)

Density at 293 K, 
r/g cm-3

1.85 1.74 1.55  2.63 3.62  5.5

Ionization energy, I/kJ mol-1







Standard electrode potential E°/V at 298 K for M2+(aq) +2e- 2M(s)

-1.70 -2.37 -2.87 -2.89 -2.90 -2.92

*For 4-coordinate.

Description of Physical Properties

  1. All are metals with two electrons in their outermost orbital and thus they form bivalent M2+ ions.
  2. The elements of Group 2 are soft but compared to elements of Group 1, they are harder and have higher cohesive energy. This is due to the contribution of two electrons per atom towards metallic bonding as compared to one electron contributed by the elements of Group 1.
  3. Their melting and boiling points are comparatively higher than those of Group 1 elements. The melting points do not vary regularly because of different structures adopted by the elements.

Fig. Melting Points of Alkaline Earth Metals

  1. The atomic and ionic radii are large but are smaller than the corresponding values of Group 1 elements. The reason behind this is the extra nuclear charge which attracts the orbital electrons more strongly.
  2. Because of the smaller atomic radii, the elements are dense than the elements of Group 1. 
  3. Because of the higher nuclear charge, the first ionization energies of elements of Group 2 are higher than the corresponding elements of Group 1. After the removal of one electron, the ratio of charges on the nucleus to orbital electrons is increased resulting in the remaining electrons being held more tightly. This makes the second ionization energies almost double of the first ionization energies.As expected, the ionization energies decrease on descending the group. The sums of first and second ionization energies are about four times the corresponding values of ionization energies of elements of Group 1.
  4. Calcium, strontium and barium impart characteristic colours to the flame. In the flame, the electrons are excited to a higher energy level. When the electron drops back to its original energy level, it emits the absorbed energy as radiation which lies in the visible region.






Flame colours of Ca, Sr and Ba are:
Element colour


Brick red


Crimson red
Ba Apple Green
  1. The standard electrode potential, E°(M2+|M), becomes more negative on descending the group. This shows that the metals become increasingly more reducing in character.
  2. Alkaline-earth metals dissolve in liquid ammonia giving bright blue colour due to the solvated electrons. These metals are not recoverable on evaporating ammonia. Instead, hexa ammoniates of the metals are obtained which slowly decompose to amides.
              M + 6NH3 M(NH3)6 M(NH2)2 + 4NH3 + H2
    Concentrated solutions of metals in ammonia are bronze coloured, due to the formation of metal clusters.
  3. The crystalline compounds of Group 2 contain more water of crystallization than the corresponding Group 1 compounds. For example, NaCl and KCl are anhydrous but MgCl2. 6H2O, CaCl2. 6H2O and BaCl2. 2H2O all have water of crystallization. The number of molecules of water of crystallization decreases as the ions become large.

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