Chemistry --structure of atom

Bohr’s model for hydrogen atom:-

Postulates for Bohr’s model:

 1.ectron in hydrogen atom move around nucleus in circular path of fixed radius and energy. these paths are called orbits.  

Energy of e does not change with time.

However, when electron move from lower to higher stationary state it absorbed sub amount of energy and energy release when it comes back.

3.     Frequency of radiations emitted or absorbed when transition of e occur is given by

Where, e1 & e2 is lower & higher energy state.

4.     Angular momentum of n electron in given stationary state is given by 

[Where n =1,2,3.....]

Limitation of Bohr’s model:-

1.     Bohr model fail to explain finer detail of hydrogen atom spectrum observed by spectroscopic, techniques.

2.     It fails to explain spectrum of other atom except hydrogen atom.

3.     It fails to explain splitting of the spectral lines in presence of electric (stark effect) or magnetic field ( Zeeman effect )

4.     Fell to explain formation of molecules from atoms by chemical bonding.

Dual behaviour of matter :-De-broglie explained that matter also behave like radiation and exhibit dual behavior means both like particle and wave like properties .

Relation

   Where  l =  wavelength.

             m = mass of particle ,

             v = velocity

p = momentum

Heisenberg’s uncertainty principle:- He explain that it is impossible to determine simultaneously the exact positive and exact momentum (or velocity) of an electron

Mathematical explanation(see text)

Aufbau principle   :- 

                              According to this principle in the ground state of the atoms the orbital’s are filled in order of their increasing energies means electrons enter higher energy orbital’s  so order in which orbital’s are filled is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

Pauli exclusion principle  :-

Two electrons in an atoms can’t have same set of 4-quantum no.

·        Only two electrons may exist in same orbital and these electrons must have opposite spin.

Hund’s  rule of maximum multiplicity :-.According to this rule pairing of  electron in the orbital’s belonging to the same sub-shell (p, d or f)

 Does not take place until each orbital belonging to that sub-shell has got one electron each i.e. it is singly occupied.