Department of Chemistry
Subject: Chemistry Subject Code: 18BSCH03
Module 2
Periodic properties and Molecular structure (12 hours)
Classification as s, p, d & f block elements, variation of atomic volume, atomic and ionic
radii ionization potential, electron affinity and electronegativity along periods and groups,
Effective nuclear charge, penetration of orbitals (shielding and de-sheilding), polarizability.
Crystal field theory and the energy level diagrams for transition metal ions and their magnetic
properties. MO Theory and Energy level diagrams – Bonding and antibonding orbitals –
Application of MO Theory to H2, He2, N2, O2, HF and CO.
1
,Classification as s, p, d & f block elements
s-block elements
Elements of groups 1 and 2 including He in which the last electron enters the s-orbital of the
valence shell are called s-block elements. There are only 14 s-block elements in the periodic
table.
p-block elements
Elements of groups 13–18 in which the last electron enters the p-orbitals of the valence shell
are called p-block elements.
d-block elements
There are three complete series and one incomplete series of d-block elements. These are: 1st
or 3d transition series which contains ten elements which atomic numbers 21–30 (21Sc – 30Zn).
2nd or 4d-transition series which contains ten elements with atomic numbers 39 – 48 (39Y –
48Cd). 3rd or 5d transition series which also contains ten elements which atomic numbers 57
and 72 – 80 (57La, 72Hf – 80Hg). 4th or 6d transition series which is incomplete at present
and contains only nine elements. These are 89Ac, 104Rf, 105Ha, Unh (Unnihexium, Z =
106), 107Ns (Neilsobohrium), 108Hs (Hassium), 109Mt (Meitherium), Uun (Ununnilium, Z
= 110) and Uud (Unundium, Z = 112) or Ekamercury. The element, Z = 111 has not been
discovered so far. Thus, in all there are 39 d-block elements.
f-Block elements
These elements are called inner-transition elements. In these elements, the f-subshell of the
anti-penultimate is being progressively filled up. There are two series of f-block elements
each containing 14 elements. The fourteen elements from 58Ce – 71Lu in which 4 f-subshell
is being progressively filled up are called lanthanides or rare elements. Similarly, the fourteen
elements from 90Th – 103Lr in which 5 f-subshell is being progressively filled up are called
actinides.
2
, Fig. Block wise categorization of elements.
1. Variation of atomic volume, atomic and ionic radii ionization potential, electron
affinity and electronegativity along periods and groups
Atomic size: In homo nuclear diatomic molecules the distance from the centre of one nucleus
to the centre of another nucleus gives the bond length and half of this bond length is atomic
radius. (Fig 4.2). The first member of each period is the largest in size. Thus we can say that
the group 1 atom are the largest in their respective horizontal rows. Similarly, atoms of group
2 elements are large but are definitely smaller than the corresponding atoms of group 1. This
3
Subject: Chemistry Subject Code: 18BSCH03
Module 2
Periodic properties and Molecular structure (12 hours)
Classification as s, p, d & f block elements, variation of atomic volume, atomic and ionic
radii ionization potential, electron affinity and electronegativity along periods and groups,
Effective nuclear charge, penetration of orbitals (shielding and de-sheilding), polarizability.
Crystal field theory and the energy level diagrams for transition metal ions and their magnetic
properties. MO Theory and Energy level diagrams – Bonding and antibonding orbitals –
Application of MO Theory to H2, He2, N2, O2, HF and CO.
1
,Classification as s, p, d & f block elements
s-block elements
Elements of groups 1 and 2 including He in which the last electron enters the s-orbital of the
valence shell are called s-block elements. There are only 14 s-block elements in the periodic
table.
p-block elements
Elements of groups 13–18 in which the last electron enters the p-orbitals of the valence shell
are called p-block elements.
d-block elements
There are three complete series and one incomplete series of d-block elements. These are: 1st
or 3d transition series which contains ten elements which atomic numbers 21–30 (21Sc – 30Zn).
2nd or 4d-transition series which contains ten elements with atomic numbers 39 – 48 (39Y –
48Cd). 3rd or 5d transition series which also contains ten elements which atomic numbers 57
and 72 – 80 (57La, 72Hf – 80Hg). 4th or 6d transition series which is incomplete at present
and contains only nine elements. These are 89Ac, 104Rf, 105Ha, Unh (Unnihexium, Z =
106), 107Ns (Neilsobohrium), 108Hs (Hassium), 109Mt (Meitherium), Uun (Ununnilium, Z
= 110) and Uud (Unundium, Z = 112) or Ekamercury. The element, Z = 111 has not been
discovered so far. Thus, in all there are 39 d-block elements.
f-Block elements
These elements are called inner-transition elements. In these elements, the f-subshell of the
anti-penultimate is being progressively filled up. There are two series of f-block elements
each containing 14 elements. The fourteen elements from 58Ce – 71Lu in which 4 f-subshell
is being progressively filled up are called lanthanides or rare elements. Similarly, the fourteen
elements from 90Th – 103Lr in which 5 f-subshell is being progressively filled up are called
actinides.
2
, Fig. Block wise categorization of elements.
1. Variation of atomic volume, atomic and ionic radii ionization potential, electron
affinity and electronegativity along periods and groups
Atomic size: In homo nuclear diatomic molecules the distance from the centre of one nucleus
to the centre of another nucleus gives the bond length and half of this bond length is atomic
radius. (Fig 4.2). The first member of each period is the largest in size. Thus we can say that
the group 1 atom are the largest in their respective horizontal rows. Similarly, atoms of group
2 elements are large but are definitely smaller than the corresponding atoms of group 1. This
3
