\(Mass\quad =\quad \frac { Charge }{ Charge/mass } \)

\(=\frac { +1.60\times { 10 }^{ -19 } }{ 9.58\times { 10 }^{ 7 } } =1.670\quad \times \quad { 10 }^{ -27 }kg\)

\({ CH }_{ 4 }(g)\quad +\quad { 2O }_{ 2 }(g)\quad \longrightarrow \quad { CO }_{ 2 }(g)\quad +\quad { 2H }_{ 2 }O(g)\\ \quad 1\quad \quad \quad \quad \quad \quad 2\quad \quad \quad \quad \quad \quad \quad \quad 1\quad \quad \quad \quad \quad \quad 2\\ volume\quad +\quad volume\quad \longrightarrow \quad volume\quad +\quad volume\\ \quad 1\times \quad \quad \quad \quad \quad 2\times \quad \quad \quad \quad \quad \quad 1\times \quad \quad \quad \quad \quad 2\times \\ 20{ cm }^{ 3 }\quad \quad +\quad 20{ cm }^{ 3 }\quad \longrightarrow \quad 20{ cm }^{ 3 }\quad \quad +\quad 20{ cm }^{ 3 }\\ 20{ cm }^{ 3 }\quad \quad +\quad 40c{ m }^{ 3 }\quad \longrightarrow \quad 20v{ cm }^{ 3 }\quad +\quad 40{ cm }^{ 3 }\)

Gay Lussac's law of combining volumes.
Gay Lussac's law:
Whenever gases react together, the volumes of the reacting gases as well as the products if they are gases bear a simple whole number ratio provided all the volumes are measured-under similar conditions of temperature and pressure.

Hydrogen combines with oxygen to form water.
2H₂ + 2O₂ \(\longrightarrow \) 2H₂O
(1 volume) + (2 volumes) \(\longrightarrow \) (2 volumes)
                 (1:2:2)
One volume of hydrogen react with two volumes of oxygen to form two volumes of water vapour.
The ratio by volume which gases, bears is 1.2:2 which is a simple number ratio.

(i) In atoms, electrons revolve around the nucleus in certain special or permissible orbits known as discrete orbits or shells or energy levels.
(ii) While revolving in these discrete orbits the electrons do not radiate energy.
(iii) The circular orbits are numbered as 1, 2, 3, 4, ... or designated as K, L, M, N, shells. These numbers are referred to as principal quantum numbers (n)
(iv) K shell (n = 1) is closest to the nucleus and is associated with lowest energy. L, M, N, .... etc are the next higher energy levels. As the distance from the nucleus increases the energy of the shells also increases.
(v) The energy of each orbit or shell is a fixed quantity and the energy is quantized.
(vi) As the distance from the nucleus increases, the size of the orbits also increases.
(vii) Maximum number of electrons that can be accommodated in an energy level is given by 2n² where n is the principal quantum number of the orbit.
(viii) When an electron absorbs energy, it jumps from lower energy level to higher energy level.
(ix) When an electron returns from higher energy level to lower energy level, it gives off energy.

(i) Atom has a very small nucleus at the centre.
(ii) There is large empty space around the nucleus.
(iii) Entire mass of an atom is concentrated in a very small positively charged region which is called the nucleus.
(iv) Electrons are distributed in the vacant space around the nucleus.
(v) The electrons move in circular paths around the nucleus.