(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

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.

A proton is the lightest positive particle. It is obtained when the gas inside the cathode rays tube is hydrogen.
Characteristics of Proton:
(i) A proton is one of the fundamental particles of the atom and is present in the nucleus of all atoms.
(ii) Charge: The charge on a proton is equal in magnitude but opposite in sign to that of an electron. Thus, it possesses a unit positive charge or + 1.6x10^-27kg which is about 1837 times of a proton is equal to that of a hydrogen atom, i.e. 1.672x^-27kg. Which is about 1897 times the mass of the electron.

Properties of anode rays:
(i) Anode rays travel straight lines. This is revealed by the fact they cast shadows of the solid objects placed in their path.
(ii) Anode rays material particles. They are capable of producing mechanical effects, e.g., they rotate a light paddle wheel placed in their path.
(iii) Anode rays are positively charged. This is shown by the fact that anode rays are deflected towards the negative plate of an electric field.

Properties of anode rays:
(i) Anode rays travel straight lines. This is revealed by the fact they cast shadows of the solid objects placed in their path.
(ii) Anode rays material particles. They are capable of producing mechanical effects, e.g., they rotate a light paddle wheel placed in their path.
(iii) Anode rays are positively charged. This is shown by the fact that anode rays are deflected towards the negative plate of an electric field.

The gas in discharged tube experiment (at low pressure and high voltage) get decomposed.Negatively charged particles are produced which travel from cathode to anode, thus facilitating the flow of current.Under other conditions, e.g., 1 atmosphere pressure, no dissociation of gas occurs and no current flows.

(i) Atomic number is defined as a number of protons present in the nucleus of an atom. For example, there are 6 protons in carbon, so the atomic number of carbon is 6. All atoms are characterized by their atomic numbers.
(ii)Mass number is defined as the sum of the total number of protons and neutrons present in the nucleus of an atom. For example, there are 6 protons and 6 neutrons in the nucleus of carbon, so its mass number is 12
(iii) Isotopes are atoms of the same element thus having the same atomic number but a different mass number. For example, chlorine has two isotopes with atomic number 17 but mass numbers as 35 and 37
(iv) Isobars are atoms that have the same mass number but different atomic numbers. Thus isobars are different elements. For example, Ne has an atomic number of 10 and sodium has an atomic number of 11 but both of these have mass numbers of 22.
Uses of Isotopes
(i) Isotope of cobalt, (⁶⁰Co), is used in the treatment of cancer.
(ii) Isotope of uranium (²³⁵U) is used as a fuel in nuclear reactors.

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.

(i)After one half-life period, the amount of isotope becomes half\(\left(1\over2\right)\).
(ii)After second half-life, the amount of isotope becomes \({1\over 4}th\) (half of half, i.e., \({1\over2}\times{1\over 2}={1\over4}\) ).
(iii)After third half-life, the amount of isotopes remains \(={1\over2}\times{1\over 4}={1\over 8}\)th of the original amount.
(iv)After the fourth half-life, the amount of isotopes remains \(={1\over2}\times{1\over 8}={1\over 16}th\)of the original amount.
Thus, \({1\over 16}\) of the original radioisotope would be left behind after four half-life periods or 3600 seconds.

Isotopes have the following uses:
(i)Treatment of diseases-Radioactive isotopes are used for the treatment of dreadful diseases like cancer.Cobalt-60 is used ti kill malignant cells in patients suffering from cancer.
(ii)Radioactive isotopes are used in chemical analysis.
(iii)Diseases in plants are investigated by using radioactive isotopes.
(iv)Production of energy: Uranium-235 can be subjected to fission process and thus production of electricity.
(v)Dating of plants, animals/humans beings obtained from ancient times after excavation by using carbon-14
(vi)I-131 is used in the treatment of thyroid disorders.
(vii)P-32 is used in the treatment of leukemia.

The number of electrons determining the combining capacity of an atom is known as its valency.For example, Oxygen has six valence electrons but to combine with other atoms it must accept two electrons to complete its octet.So its valency is -2.The valency of lithium, sodium is one as these lose one electron each when combine with other atoms and complete their octets.In general, if the atom 1, 2 or 3 electrons in its outermost shell, then valency is equal to the valence electrons.When the number of electrons in the outermost shell of an atom is close to its full capacity, i.e., 5, 6 or 7 then the valency is equal to the number of electrons by adding which the shell may become complete or 8 minus valence electrons.

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.