Here we are providing the short notes on Chemistry which will be help to crack science part in may examinations like SSC, Railway and other competitive exams.
CLASSIFICATION OF ELEMENTS
Mendeleef’s Periodic Table (1869)
States that,“the physical and chemical properties of elements are the periodic function of their atomic masses.”
Modern Periodic Law
“The physical and chemical properties of the elements are periodic function of their atomic numbers.”
Long Form of Periodic Table
Long form of periodic table or Bohr’s table is based on Bohr-Burry concept of electronic configuration. It contains 7 periods (horizontal rows) and 18 groups.
Periodic Properties
The properties which are repeated at regular intervals are known as periodic properties, i.e. periodic properties show a regular order along a group and period. Some important periodic properties are
Ionisation enthalpy
It is the minimum energy required to remove an electron from an isolated gaseous atom of an element to form a positive ion.
Electron gain enthalpy
It is the energy released by an element when an extra electron is added to its neutral gaseous atom.
Electronegativity
It is the ability of an atom to attract the shared pair of electrons towards it.
Metallic character
It is the tendency of an element to form cation by the loss of electrons.
