ICSE Class 7 Answered

Properties of Electrons

• An electron, which is denoted as e^-, is the fundamental particle with a negative charge.
• Its properties are independent of the gas in the discharge tube.
• The mass of an electron is negligible and its charge is -1.
• The mass of an electron is extremely small. It is of the mass of a hydrogen atom (9.108 ´ 10^-28 g) and so its mass is considered almost negligible. (Hydrogen is an atom of the lowest mass). Since the mass of a hydrogen atom is 1 u, we can say that the relative mass of an electron is u.
• The absolute mass of an electron is 9 ×10^-28 grams.
• Its charge is 1 unit negative charge, i.e. 1.602 ´ 10^-19 coulombs.
• The tiny electrons revolve around the nucleus of the atom in specific orbits or shells.

Properties of Protons

• Proton is denoted as p⁺, and is the fundamental particle with a positive charge.
• The mass of a proton is taken as 1 unit and its charge as +1.
• The mass of a proton was calculated as being equal to the mass of an atom of hydrogen, i.e. 1.672 ´ 10^-24 g. The relative mass of a proton is 1 u.
• If we compare the mass of a proton with that of an electron, then the mass of a proton is 1840 times that of an electron.
• The absolute mass of a proton is 1.6 ´ 10^-24 grams.
• The charge of a proton is equal and opposite to the charge of an electron, i.e. 1.602 × 10^-19 coulomb of positive charge.

 The formation of cathode rays and anode rays on passing an electric current through the gases at a very low pressure shows that an atom is divisible. It is made up of smaller particles.