Vidyabharti College Seloo

Department of Chemistry

Class :- B.Sc. Third Sem.

Presented by :-

Introduction :-

According to modern classification, the elements have

been classified into s, p, d and f-block elements. The base

of this classifications is the position of last electron.

The elements in which last electron enters into s-subshell

are known as s-block elements, those in which last

electron enters into p-subshell are known as p-block

elements, those in which last electron enters into d-

subshell of last but one (n-1)th main shell are known as

d-block elements whereas, those in which last electron

enters into f-subshell of last but two (n-2)th main shell

are known as f-block elements.

The d-block elements are placed in between s and p –block elements in the periodic table and have properties intermediate between s & p – block elements. Hence they are also known as transition elements. 3d- series is also known as first transition series It includes ten elements from Scandium (21) to Zinc (30)

POSITION OF TRANSITION

ELEMENTS IN PERIODIC TABLE

The transition elements occupy or hold a central position

in the periodic table.

They are placed in between s-block elements and p-block

elements.

Whereas, in case of d-block elements, there is gradual

decrease in ionic character and increase in covalent

character from left to right in the periodic table, thus d-

block elements are known as transition elements.

S - block p- block

Fourth transition series

Second transition series

Third transition series

First transition series

Lanthanides

Actinides

Transition elements

Position of Transition elements in periodic table

GENERAL PROPERTIES OF

TRANSITION ELEMENTS:-

The d-block elements are peculiar in their properties. All

the d-block elements are metals. Due to the some of

their characteristic properties, d-block elements are

important, which are as under.

1. The d-block elements are metals having high melting and boiling points.

2. Most of the transition elements are good conductors of heat and electricity.

3. They have high densities due to smaller atomic sizes & high atomic weights.

4. They show variable oxidation states.

5. Their compounds are generally paramagnetic in nature.

6. They have a good tendency to form coloured

compounds and complexes.

7. Most of the transition elements such as Mn, Ni, Co, Cr,

V, Pt and their compounds are used as catalysts.

8. They are good reducing agents.

PROPERTIES OF

FIRST TRANSITION SERIES ELEMENTS

ELECTRONIC CONFIGURATION :-

First transition series elements i.e. Scandium (Sc=21) to Zinc (Zc=30), belong to 3d series and thus, the last electron enters into 3d subshell. First transition series includes elements from Scandium (21) to Zinc (30). In case of Argon (Ar=18), the 18 electrons are distributed as 1s2, 2s2, 2p6, 3s2, 3p6. In Scandium (Sc=21), the next electron goes to 3d subshell according to aufbau principle. Hence , Scandium is the first element of transition series. After Scandium, each successive electron adds to 3d subshell till its capacity is fulfilled. Hence, the general electronic configuration is written as, [Ar] 4s1or2, 3d1-10.

ATOMIC AND IONIC RADII

Atomic radius :-

The distance of outer most electron from the center of nucleus in

an atom is known as atomic radius.

Ionic radius :-

The effective distance from the nucleus of the ion upto the point

of influence of nucleus is known as ionic radius.

The atomic or ionic radius are depends upon three factors, which

are as follows.

I. Nuclear charge

II. Number of shells

III. Screening effect (shielding effect)

IONIZATION POTENTIAL

“The minimum energy required to remove most loosely bound

outermost electron from isolated gaseous atom in its ground

state is known as ionization potential or ionization energy”.

The energy required to remove first electron from isolated

gaseous atom is known as first I. P., and energy required to

remove second electron is known as second I. P.

Ionization potential depends upon :-

I. Nuclear charge

II. Number of shells

III. Screening effect (shielding effect)

OXIDATION STATES:-

The number of electrons lost or gained by an atom during

formation of compound is known as its oxidation state. When

electron are lost, the oxidation states is positive. If electrons are

gained, oxidation state is negative.

All the metals have a tendency to show positive oxidation states by

loss of electron due to low values of their ionization potentials.

Minimum oxidation state :- Except chromium and copper, all the elements show +2 as minimum oxidation state. This is because of loss of two 4s electrons whereas, in case of Cr and Cu, there is only one electron in the 4s subshell. Hence, they show +1 as minimum oxidation state.

Maximum oxidation state

Maximum oxidation state goes on increasing when we move from

left to right across the period i.e. from Sc to Mn. It is due to loss of

total number of electrons in 4s and 3d subshell. The maximum

oxidation state shown by 3d series element is +7 for Mn. Thus,

upto Mn, the maximum oxidation state is equal to number of

electrons in 3d and 4s orbitals.