Classification of Elements
Mendeleev periodic law :-
Mendeleev explanation that properties of the elements are periodic function of their atomic weights.
Modern periodic law :-
Moseley (1913) according to this law physical & chemical properties of the elements are periodic functions of their atomic numbers.
s – Block elements: –
Elements of group 1 (Alkali metals) with ns2 outermost electronic configuration.
p – Block elements: –
These elements belong to group no. 13 to 18.
d – Block element: –
These are elements of group no. 3 to 12 in centres of periodic table. Also known as the transition elements.
f– Block element: –
These have 2 – rows of elements at bottom of periodic table. i.e. lanthanides Ce (z = 58) to Lu (z = 71) Actinides Th (z = 90) to Lr (z = 103) .
These are more than 78% of all known elements. And present in the left side of periodic table.
Non – metals :-
These present in the top right hand side of periodic table.
Elements which show character of both i.e. metals and non – metals are known as metalloids or semi-metals.
Periodic trends in physical properties:-
1. Atomic radius:-
2. Ionic radius:-
On general, the trend of ionic radius is same as that of atomic radius.
3. Ionization enthalpy :-
Quantitative measure of tendency of an element to loose electron is known as ionization enthalpy.
4. Electron Gain enthalpy :-
When an electron is added to a neutral gaseous atom to convert it into a – ve ion, the change in enthalpy in the process is given by electron gain enthalpy.
5. Electronegativity: –
The qualitative measure of ability of atom to attract shared electrons from chemical compound (or chemical bond) toward itself is known as electronegativity.
Periodic trends in chemical properties:–
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