Continous sub-division of matter would ultimately be led to atoms which are further indivisible. It was further observed that atoms contain sub-atomic particles that are Proton, Neutron or Electron.
J.J Thomson Model of Atom
As per Thomson’s Model of atom posses, a spherical shape in which positive charge is uniformly distributed. Electrons are embedded in such a manner so as to give most stable electrostatic arrangement.
Thomson’s Model is also known as watermelon model or raisin pudding model.
Rutherford’s Model consists of an element Polonium with a reflection plate, a screen and a gold foil.
When alpha rays are bombarded on gold foil then following observations were observed.
- Most of the rays went undeflected.
- A small fraction of rays was deviated by some angle indicating that some opposite force was attracting then that was Proton.
- A very few that is 1/20000 bounced back indicating that there is a neutral charge that was Neutral.
Based on these observations following conclusions were made
- Most of the space in an atom is empty as most rays went undeflected.
- A positive charge has to be concentrated in a very small volume that repels and deflected the positively charged particles. This is known as Nucleus.
- Electrons move around the nucleus in circular orbit path called Orbit.
Drawbacks of Rutherford’s Model
According to Maxwell’s Theory, electromagnetic radiations charged particles when accelerated should emit electromagnetic radiations. Therefore electrons will lose energy and will get merged into the nucleus which is contradictory to what is observed. Thus it cannot explain the stability of an atom. Practically it would have taken 10-18 seconds for the electron to spirally merged into the nucleus.
These are energy carriers and they travel in the form of a wave. Wave motion is perpendicular to the electric and magnetic field.
- When electron revolves in a particle orbit, it doesn’t lose or absorbs energy until then external energy is applied to it.
- When an electron jumps from the first orbit to another it’s energy may increase to decrease. The original state of the electron is known as its ground state and when it jumps from one orbit to another it is known as the excited state.
- Electron revolves in those orbits which have angular momentum in integral form.
- Bohr’s model is valid only for single electron species like H, He and Li
Calculation of Energy
Law of Quantization of Energy
As per this law, the energy of the electron (e–) is quantized that means electron will jump from the first but to another if and only if the exact amount of energy is required or supplied.
When an electron jumps from a higher orbit to lower orbit then it emits energy in the form of radiations. This radiations have different wavelength and are known as spectral lines.