The nucleus is a heavily charged positive centre located in a very small space of around 10 ^-15 m.An electron is a very small negatively charged particle with well established charge to mass ratio.The charge on electron forms the smallest unit of charge on atomic particles.

An electron is a negatively charged particle, whereas a proton is a positively charged particle. The magnitude of their charges is equal. Therefore, an atom containing one electron and one proton will not carry any charge. Thus, it will be a neutral atom.

The statement is true because:
(i) Whatever be the nature of the gas or the material of the cathode, the electrons have the same charge to mass(e/m) ratio i.e., 1.7589x10¹¹ coulomb per kg
(ii) The electrons obtained by different methods are identical.

A discharge tube is a glass tube about 70cm long and having a diameter of 5cm.Two metal electrodes are sealed at the two ends, one of which is connected to the negative terminal of a battery and the other to the positive terminal.A side tube is fused at the centre of the glass tube which serves to pump out air from it, using a suction pump.

(i)Cathode rays travel in straight lines and thus cast shadows of objects placed in their path.
(ii)Cathode rays possess material particles because they can rotate a light paddle wheel placed in their path.
(iii)They are deflected towards positive plate thus showing that theses are negatively charged particles knowns as electrons
(iv)They ionise  gas through which they pass
(v)They are deflected by magnetic fields.
(vi)The nature of cathode rays is independent of the material of cathode.Hence they are common constituents of all matter
(vii)They can penetrate through thin metallic sheet
(viii)They can produce X-rays
(ix)The mass of a cathode ray particle is very-very small as compared to the mass of the atom from which it is formed

(i)Cathode rays travel in straight lines and thus cast shadows of objects placed in their path.
(ii)Cathode rays possess material particles because they can rotate a light paddle wheel placed in their path.
(iii)They are deflected towards positive plate thus showing that theses are negatively charged particles knowns as electrons
(iv)They ionise gas through which they pass
(v)They are deflected by magnetic fields.
(vi)The nature of cathode rays is independent of the material of cathode.Hence they are common constituents of all matter
(vii)They can penetrate through thin metallic sheet
(viii)They can produce X-rays
(ix)The mass of a cathode ray particle is very-very small as compared to the mass of the atom from which it is formed

Canal rays are positively charged radiations. These rays consist of positively charged particles known as protons. They were discovered by Goldstein in 1886.

Following rules are followed to fill electrons in different energy levels.
(i) If n gives the number of orbit or energy levels, then 2n² gives the maximum number of electrons possible in a given orbit or energy level. Thus
The first orbit or K-shell will have 2n² = 2 x 1² = 2 electrons
The second orbit or L-shell will have 2n² = 2 x 2² = 8 electrons
The third orbit or M-shell will have 2n² = 2 x 3² = 18 electrons
(ii) If it is the outermost orbit, then it should have not more than 8 electrons.
(iii)There should be the stepwise filling of electrons in different orbits, i.e., electrons are not accommodated in a given orbit if the earlier orbits or shells are incompletely filled.
Thus, eighteen electrons would be accommodated as: K = 2, L = 8, M = 8.

Bohr and Bury gave the following rules for the distribution of electrons around the nucleus.
(i)Electron ar revolving around the nucleus in different orbits or shells.hese energy shells are represented by numbers 1, 2, 3, 4 or K, L, M, N.
(ii)The maximum number of electrons in any shell cannot exceed 2n², where n is the number of that energy level.Thus for
K-shell, n=1, no. of electrons=2x1²=2
L-shell, n=2, no. of electrons=2x2²=8
M-shell, n=3, no. of electrons=2x3²=18
N-shell, n=1, no. of electrons=2x4²=32
(iii)The outermost orbit of an atom cannot have more than 8 electrons and the next to the outer shell (penultimate shell) can have at the most 18 electrons.
(iv)It is not absolutely necessary that an orbit has its full quota of electrons before starting to fill the next higher orbit but the shells are filled in a stepwise manner