Electron

In 1830, Michael Faraday showed that when electricity is passed through a solution of an electrolyte, chemical reactions occurred at the electrodes, which resulted in the liberation and deposition of matter at the electrodes. This suggested the particulate nature of electricity.
A Crookes tube is an early experimental electrical discharge tube, invented by British physicist William Crookes. It consists of a partially (but not completely) evacuated glass cylinder of various shapes, with two metal electrodes at either end. When a high voltage is applied between the electrodes, current starts flowing through a stream of particles traveling in straight lines from the cathode to the anode. These were called cathode rays or cathode ray particles.
If the anode is perforated, and the anode end of the tube is coated with phosphorescent material zinc sulphide, a bright spot on the coating is developed (which is the principle in tv sets too).

1. Cathode rays start from cathode (-ve) and move towards anode (+ve)
2. These are not visible themselves. But fluorescent and phosphorescent materials glow when hit by them.
3. These rays travel in straight lines in the absence of electrical or magnetic field.
4. In their presence, they travel like negatively charged particles (suggesting that these contain -ve particles, electrons)
5. The characteristics of cathode rays do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube.

Charge to mass ratio:
In 1897, J J Thomson (British physicist) measured the ratio of electrical charge (e) to the mass of electron (m_e) by using CRT and applying electrical and magnetic field perpendicular to each other as well as to the path of electrons. Thomson argued that the amount of deviation of the particles from their path in the presence of electrical or magnetic field depends upon:

1. the magnitude of -ve charge on the particle (directly proportional to deflection)
2. mass of the particle (inversely proportional to deflection)
3. the strength of the electrical or magnetic field (directly proportional to the deflection)

Thomson calculated
e/m_e = 1.758820 × 10¹¹ C kg ^-1
where m_e is the mass of the electron in kg and e is the magnitude of the charge on the electron in coulomb (C). Since electrons are negatively charged, the charge is -e.

Charge on electron:
RA Millikan devised oil drop experiment to determine the charge.
He found −1.6×10⁻¹⁹ C as the value. The present value is −1.6022×10⁻¹⁹ C.
The mass of the electron therefore is
m_e = e/(e/m_{e) =} −1.6022×10⁻¹⁹ C / 1.758820 × 10¹¹ C kg ^-1 = 9.1094 × 10^-31 kg