S Block: Group 2

Question 1

Electronic configuration

Answer 1

Be: [He]2s2
Mg: [Ne]3s2
Ca: [Ar]4s2
Sr: [Kr]5s2
Ba: [Xe]6s2
Ra: [Rn]7s2

Question 2

Atomic or ionic radii

Answer 2

Smaller alkali metals, increase down the group. The divalent ions (M2+) are smaller than the parent atom

Question 3

Ionisation Enthalapy

Answer 3

The 1st IE of alkaline earth metals are higher than that of alkali metals due to smaller size. But the 2nd IE are smaller than corresponding alkali metals.

Question 4

Hydration Enthalapy

Answer 4

Larger than alkali metals due to greater charge density.
Be2+ > Mg2+ > Ca2+ > Sr2+ > Ba2+
Salts are more extensively hydrated eg MgCl2.6H2O, CaCl2.6H2O

Question 5

Density

Answer 5

Denser, heavier and harder thank alkali metals due to small size and strong metallic bonds. Increases down the group

Question 6

State

Answer 6

Silvery white, harder than alkali metals

Question 7

conductors

Answer 7

good conductors of heat and electricity

Question 8

MP and BP

Answer 8

higher than alkali metal due to smaller size but doesnt show regular trend

Question 9

Flame colour

Answer 9

Be & Mg do not impart color as the electrons are strongly bound to get excited by flame (high ionisation enthalpies).
Ca: Brick red
Sr: Crimson red
Ba: apple green

Question 10

Reducing properties

Answer 10

lower than alkali metals because of higher IE

Question 11

Reaction w air

Answer 11

Be and Mg- kinetically inert to O2
- except Ba and Ra(peroxides), rest form form oxides
2Be + O2 →  2BeO
2 Mg + O2 →  2 MgO
2Ca + O2 →  2CaO
Ba + O2 →  BaO

Question 12

Reaction w acids

Answer 12

• Readily react with acids to liberate H2

M + 2HCl → MCl2 + H2

Question 13

Nature of oxides

Answer 13

BeO is a covalent solid, the oxides of the rest of the metals are white crystalline ionic solids
- Except for BeO which is amphoteric in nature, rest of the oxides are basic & the basic strength increases down the group
MO + H2O → M(OH)2

Question 14

Reaction w water

Answer 14

• Be & Mg are kinetically inert due to formation of an oxide layer.
  
  • Ca, Sr & Ba are readily react with water with increasing vigour even in cold to form hydroxides

Question 15

Nature of hydroxides

Answer 15

• Less basic & less stable than alkali metals.
• Due to low IE of metals, M-OH bond ionizes, releasing OH-.
• Basic strength increases down the group due to decrease in IE.
• Be(OH)2 is amphoteric in nature
Be(OH)2 + 2OH- → 🡪 [Be(OH)4]2- (Berrylate ion)
Be(OH)2 + 2HCl +2H2O → 🡪[Be(OH)4]Cl2

Question 16

Reactivity towards halogen

Answer 16

• Combine with halogens at elevated temperature.
• Ionic character increases from Be to Ra.
• BeCl2 in solid state has a polymeric chain structure.
In vapour state BeCl2 forms a dimer with Cl as a bridge which dissociates into a linear monomer at high temperature.
Tendency to form hydrated halides decreases down the group. (MgCl2.8H2O; CaCl2.6H2O, BaCl2.2H2O)

Question 17

Reactivity towards hydrogen

Answer 17

• All the elements except Be combine with H2 to form MH2.

* BeH2 & MgH2 are covalent & polymeric whereas others are ionic.

Question 18

Salts of Oxo - acids ( H+ on hydroxyl group) (Carbonates & bicarbonates)

Answer 18

• Carbonates are insoluble in water & their solubility decreases with increase in at.no. of metal ion.
• Thermal stability increases with increase in cationic size. BeCO3 is unstable & is stored only in the atmosphere of CO2.
• Sulphates are thermally stable & white in color.
• The solubility of sulphates decreases down the group because SO42- is large & masks the cation in lattice thus the size of cation does not influence lattice energy but hydration energy decreases from Be2+ to Ba2+.
• Nitrates are prepared by dissolution of carbonates in dil HNO3.
• The tendency to form hydrated nitrates decreases with increase in size of cation.
• All nitrates decompose on heating to give oxide.
2M(NO3)2 → 2MO + 4NO2 + O2

Question 19

Berellium vs other alkali earth metals

Answer 19

1) Be has higher MP & BP than other alkali earth metals.
2) BeO is amphoteric while others are strong bases.
3) Be & Mg do not impart color to the flame.
4) Be does not form peroxides.
5) BeSO4 is soluble in water.
6) Be does not liberate H2 from acids whereas others do

Question 20

Be and Al are similar as

Answer 20

1) The charge/ radius ratio is nearly the same.
2) Both are not readily attacked by acids due to formation of protective oxide layer.
3) Hydroxides of both dissolve in excess of alkali to give ‘ate’ ion i.e. [Be(OH)4]2- (Berrylate ion) & [Al(OH)4]-(Aluminate ion)
4) The chlorides of Be & Al have bridged Cl- in their vapour phase.