ionic bond

                                                        Bohr's Atomic Model

          Neil Bohr in 1913 A.D.,formulated on atomic model by based on planks quantum theory of radiation and some classed concept of physician the early 20th century, experiments by Ernest Rutherford  established that atoms consisted of a diffuse cloud of negatively

charged electrons surrounding a small, dense, positively charged nucleus. Given this experimental data, Rutherford naturally considered a planetary-model atom, the Rutherford model of 1911 – electrons orbiting a solar nucleus – however, said planetary-model atom has a technical difficulty. The laws of classical mechanics (i.e. the Larmor formula), predict that the electron will release electromagnetic radiation while orbiting a nucleus. Because the electron would lose energy, it would rapidly spiral inwards, collapsing into the nucleus on a timescale of around 16 picoseconds. This atom model is disastrous, because it predicts that all atoms are unstable.

Also, as the electron spirals inward, the emission would rapidly increase in frequency as the orbit got smaller and faster. This would produce a continuous smear, in frequency, of electromagnetic radiation. However, late 19th century experiments with electric discharge have shown that atoms will only emit light (that is, electromagnetic radiation) at certain discrete frequencies.

To overcome this difficulty, Neils Bohrs  proposed, in 1913, what is now called the Bohr model of the atom..This atomic model has following assumptions:

1. Electron revolves arround the nucleus in a selected circular path called orbit.                                                                                                         
                                                                                                                                                                                                                                                            
2. Electrons  doesnt loose or gains energy when revolves around the nucleus. Such a state of electron is called stationary state.Stationary means energy of electron is constant but its motion change with time.The postulate justify about the statibility of atom.
3. The centrifugal force of electron, which tends to pull away electron from its orbit is balanced by electrostatic force of attraction between nucleus and electron,                                                                                       where m_e is the electron's mass, e is the charge of the electron, k_e is coulombs constant and Z is the atom's atomic number.             
4. Electron can revolve only in those orbit in which angular momentum of revolving electron is an integral multiple of h/2π. This postulates shows that the angular momentum is quantized.
5. Electron can absorb or emit energy when electron absorbs energy. It gets excited.The excited of electron/atom is highly unstable, so electron jumps from higher energy level to lower energy level by emitting energy in the form quantum of radiation which can be calculated by using planks's quantum theory of radiation.                                                                                                              where h= planck constant                                                                  
The radius of electron can be determined by using formula:




It also determines the electron's total energy at any radius: