(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

Cathode rays are made up of negatively charged particles called electrons.The nature of cathode rays does not depend on the nature of the gas from which theses are produced.The mass of a cathode ray particle is very small compared to the mass of the atom from which it is formed.These particles were found to be about 2000 times smaller in mass than the hydrogen atom.
Anode rays are a stream of positively charged particles.The mass of an anode ray particle is equal to the mass of the atom from which it is formed.The nature of the anode rays depends on the gas from which these are produced.

(i) The mass of an electron is about 1/1840 that of a hydrogen atom, i.e., about 9.0x-10^-31kg.
(ii) An electron is a negatively charged particle and has a charge of 1.6x10^-19 coulomb. This is one unit of charge.

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.

(a) Isotopes of an element are chemically similar because these have the same electronic configuration
(b) An atom is electrically neutral because it contains an equal number of positive charges (protons) and negative charges (electron).
(c) Noble gases show least reactivity because these have the outermost octet completely filled up
(d) The massive particles protons and neutrons are located in the nucleus of an atom.
(e) Ions are formed after completion of the octet and so are more stable than the atoms.

Amount of actinium left after 15 seconds \(={1\over2}\times0.1=.05g\)
Amount of Actinium left after another 15 seconds (i.e., 30 seconds) \(={1\over2}\times.05=.025g\)
Amount of Actinium left after another 15seconds (i.e., 45 seconds)\(={1\over2}\times0.25=.0125g\)
Amount of Actinium left after another 15 seconds (i.e., 60 seconds=1 min.)\(={1\over2}\times.0125\)
=.00625 g=6.25mg.

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.

(i)When  \(\alpha\)-particles are allowed to strike a very thin gold foil, it is found that most of these particles pass through the foil without any deflection.It is calculated that one particle in 10⁵ deflected back by 180⁰ showing that a larger part (10⁵:1)of the atomic space is empty
(ii) The fact that atomic nuclei are positively charged can be shown by performing Rutherford's  \(\alpha\)-particle scattering experiment. Take a thin sheet of metal foil.Allow  \(\alpha\)-particle to bombard over it. It will be observed that only a small fraction of  \(\alpha\)-particles (positively charged) are deflected through large angles and the rest pass through the foil without any deflection. This shows that the positive charge of the atom is concentrated at the center of the nucleus.