Niels Bohr Atomic Theory

An atom is made up of three particles, electrons, protons and neutrons. Electrons have a negative charge and protons have a positive charge whereas neutrons have no charge. They are neutral. Due to the presence of equal number of negative electrons and positive protons, the atom as a whole is electrically neutral.

The protons and electrons are located in a small nucleus at the center of the atom. Due to the presence of protons, the nucleus is positively charged.

The electrons revolve rapidly around the nucleus in fixed circular paths called energy levels or shells. The 'energy levels' or 'shells' or 'orbits' are represented in two ways: either by the numbers1, 2, 3, 4, 5 and 6 or by letters K, L, M, N, O and P. The energy levels are counted from center outwards.

Each energy level is associated with a fixed amount of energy. The shell nearest to the nucleus has minimum energy and the shell farthest from the nucleus has maximum energy.

There is no change in the energy of electrons as long as they keep revolving with the same energy level. But, when an electron jumps from a lower energy level to a higher one, some energy is absorbed while some energy is emitted.

When an electron jumps from a higher energy level to a lower one, the amount of energy absorbed or emitted is given by the difference of energies associated with the two levels. Thus, if an electron jumps from orbit 1 (energy E1) to orbit 2 (energy E2), the change in energy is given by E2- E1.

The energy change is accompanied by absorption ofradiation energy of E = E2E1= hwhere, h is a constant called'Planck's constant'and is the frequency of radiation absorbed or emitted. The value of h is 6.626 x 10-34J-s. The absorption and emission of light due to electron jumps are measured by use of spectrometers.