Introduction of p- block
- P block is present at extreme right of periodic table.
- It has general electronic configuration ns2np1-6.
- It includes solids, liquids and gases.
- The elements of this group are metal, non- metal and metalloids.
- If we move along period in periodic table, non-metallic character increases and if we move down the group, the non-metallic character decreases.
- In this group: As we move down, the lower oxidation state becomes more stable due to” Inert pair effect.”
Inert pair effect : It is “reluctance in the participation of s electrons in bond formation due to poor shielding effect by d and f orbital .As a result, s electrons are tightly bounded .
1st member is different from its congeners due to:
- Small size
- Highest ionization energy.
- High electro-negativity.
- No vacant d orbital.
- They show maximum co-valence of 4 because of no vacant d orbital.
- First member also has tendency to form multiple bonds because in them p can takes place (because of its small size) .
Physical properties of group 13:
- Atomic size and Ionic radii:
- If we compare group 11 with group 13, then group 13 is smaller due to increased nuclear charge.
Example: Out of Be and B ,Boron is smaller .
- Down the group, size increases because nuclear charge decreases (due to addition of new shell).
- Expected order : B <Al<Ga<In<Tl
- But actual the order is :BGa<In<Tl
- The reason behind it: Is due to filling of d-orbital in Gallium, the effective nuclear charge on valence electron increases (because of poor shielding effect by d and f orbital).
- Therefore, nucleus pull electron more effectively and size decreases.
- That is the reason, Gallium is smaller than Aluminum (because Gallium has d-electrons and Aluminum doesn’t have) .
- Ionization energies
- If we compare ionization energy of group 13 and group 2, we can say that the ionization of group 13 is more, because of their small size and increased nuclear charge.
- But actually group 2 has high ionization energy, than group 13 due to completely filled s orbital in group 2 elements.
- In case of Be and B, the electronic configuration of Be is 1s22s2 and in boron it is 1s22s22p1. So, due to this reason the ionization energy of Boron is less than Beryllium.
Down the group ionization energy decreases, as the size increase and nuclear charge decrease.
So , the expected order is : B>Al>Ga>In>Tl
But actually it is : B>AlIn>Tl due to poor shielding effect by d electrons in gallium.
- Electronegativity: If we compare with group 2, they are more electronegative due to increased nuclear charge.
Along group: It decreases, but the expected order is this B>AlIn>Tl.
This is due to poor shielding effect.
- Electropositive character: As compared to group 2, they are less electropositive due to increased nuclear charge.
Down the group: The size increases. Therefore, metallic character increases.
B Al Ga In Tl
Non metal amphoteric less metallic metallic metallic
- Oxidation state: It depends on electronic configuration .As their electronic configuration is ns2 np.So, oxidation states shown by them are +3,+1.
- Boron: Shows exceptional behavior because of its small size and high ionization energy .It actually faces difficulty in loosing electrons .Therefore, it forms covalent bond.
B Al Ga In Tl
(+3) (+3) (+3,+1) (+3,+1) (+1)
This is basically due to inert pair effect.