Canal rays are beam of positively charge particles. They are also known as Anode rays. It was discovered by E. Goldstein in 1886 in a gas discharge tube.

There will be no charge (neutral) on atom as charge on electron and proton is equal and opposite.

According to J. J. Thompson, an atom consists of a positively charged sphere and the negatively charged electrons are embedded in it. The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

If Rutherford’s α-particle scattering experiment is carried out using a foil of other metal rather than gold then we will also get similar observations. Since, other metals foil can’t make thin as gold so more α-particles will rebound and we do not get good result as using thin foil of gold(highly malleable).

Three sub-atomic particles of an atom are (i) Electron (ii) Proton (iii) Neutron

Atomic mass = Number of protons+ Number of neutrons
4 = 2 + Number of neutrons
Number of neutrons = 2

For Carbon atom-
Carbon atomic number = 6
It’s electronic configuration is C = 1s2 2s2 2p2
So, electrons will be distributed as,
In the inner most orbit (n=1, 1s2 ) or K-shell = 2 electrons
In the second orbit (n=2, 2s2 2p2) or L-shell = 4 electrons

For Sodium atom-
Sodium atomic number = 11
It’s electronic configuration is Na = 1s2 2s2 2p6 3s1
So, electrons will be distributed as,
In the inner most orbit (n=1, 1s2 ) or K-shell = 2 electrons
In the second orbit (n=2, 2s2 2p6 ) or L-shell = 8 electrons
In the third orbit (n=3, 3s1 ) or M-shell = 1 electron

Maximum number of electrons in K-shell = 2 electrons
Maximum number of electrons in L-shell = 8 electrons
Total number of electrons in the atom = 2 + 8 = 10 electrons

“Valency of an atom is definite combining capacity of an atom with other atoms when it forms chemical compounds/ molecules or number of that electrons which atom loses/accept to complete it’s octoate.”
Valency of an atom is determined by
(i) If the number of electrons in the outermost shell of the atom of an element is less than or equal to 4, then the valency of the element is equal to the number of electrons in the outermost shell.
Distribution of electrons in Mg (Z = 10) = 2,8.2
Since, outermost shell have 2 electrons so,The valency of magnesium = 2

(ii) If the number of electrons in the outermost shell of the atom of an element is greater than 4, then the valency of that element is determined by subtracting the number of electrons in the outermost shell from 8.
Distribution of electrons in Cl (Z = 17) = 2,8.7
Since, outermost shell have 7 electrons so,The valency of chlorine = 8 −7 = 1

Distribution of electrons in S (Z = 16) = 2,8.6
Since, outermost shell have 6 electrons so,The valency of chlorine = 8 − 6 = 2

(i) Atomic number = number of electrons = number of protons = 8
(ii) Charge on the atom = 0 (If number of electrons is equal to number of protons in an atom then total charge on atom is zero )

Limitation: It could not explain the origin of spectral series of H atom and also result of Rutherford α -Particle Scattering Experiment.

Limitations of Rutherford’s Atomic Model:
(i) Rutherford’s atomic model cannot explain the stability of an atom.
(ii) In Rutherford’s atomic model an electron can revolve in orbits of all possible radii .so it should emit a continuous spectrum. But an atom like hydrogen always emits a discrete line spectrum.

Bohr’s Atomic Model
(i) An atom consists of a small and massive central core, called Nucleus; electrons revolve around nucleus in circular orbit like planetary motion.
(ii) Only certain special orbits known as discrete orbits (non-radiating orbits or Stationary Orbits) of electrons, are allowed inside the atom. While revolving in discrete orbits the electrons do not radiate energy.
(iii) An atom can emit or absorb radiation only when an electron jumps from one orbit to another orbit.

According to Bohr and Bury, following rules are used for distribution of electrons in different energy levels or shells for the first eighteen elements:
(i) Maximum number of electrons that can be present in a shell is determined by the formula 2n², where ‘n’ – orbit number or energy level index, 1,2,3,….
So, maximum number of electrons in different shells will be,
First orbit(n=1) or K-shell will be = 2 × 1² = 2,
Second orbit(n=2) or L-shell will be = 2 × 2² = 8,
Third orbit(n=3) or M-shell will be = 2 × 3² = 18,
Fourth orbit(n=4) or N-shell will be = 2 × 4²= 32, and so on.
(ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8.
(iii) Filling of electrons in shells is done in step-wise manner i.e. Electrons are not accommodated in a given shell, unless the inner shells are empty (not completely filled).

VALENCY : “Valency of an atom is definite combining capacity of an atom with other atoms when it forms chemical compounds/ molecules or number of that electrons which atom loses/accept to complete it’s octoate.”
Valency of an atom is determined by
(i) If the number of electrons in the outermost shell of the atom of an element is less than or equal to 4, then the valency of the element is equal to the number of electrons in the outermost shell.
Distribution of electrons in Si (Z = 14) = 2,8.4
Since, outermost shell have 4 electrons so,The valency of Silicon = 4

(ii) If the number of electrons in the outermost shell of the atom of an element is greater than 4, then the valency of that element is determined by subtracting the number of electrons in the outermost shell from 8.
Distribution of electrons in O (Z = 8) = 2,6
Since, outermost shell have 6 electrons so,The valency of Oxygen = 8 – 6 = 2

(i) Atomic number (Z): The total number of protons in an atom is equal to atomic number, which is also equal to number of electrons in that atom at neutral state.
For example, the atomic number of Helium is 2. It means He contains 2 protons and 2 electrons.

(ii) Mass number (A): Mass number of an atom is equal to total number of protons and neutrons present in a nucleus.
Mass number of an atom = Number of protons + Number of neutrons
For example, the atomic number of Sodium is 11 which, is equal to the number of protons, the number of neutrons in Sodium is 12.
So, The mass number of Sodium is equal to 23 (11+12).

(iii) Isotopes: The atoms of an element which have the same atomic number but different mass number are called isotopes.
For example, Hydrogen has three isotopes:
Hydrogen Protium (₁H¹) – its nucleus has one proton;
Deuterium (₁H²)-its nucleus has one proton and one neutron;
and Tritium (₁H³) –its nucleus has one proton and two neutrons.

Uses of Isotopes:
(a) Isotopes of Uranium are used in Nuclear reactor.
(b) Isotopes of Carbon are used in Radio Carbon dating.
(c) An isotope of Cobalt is used in the treatment of cancer.

(iv) Isobars: The atoms having the same mass number (A) but different atomic number.
For example: (₁₇Cl³⁷) and (₁₆S³⁷), as both have same mass number = 37.
(₂₀Ca⁴⁰) and(₁₈Ar⁴⁰), as both have same A = 40.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

On the basis of Rutherford’s model of an atom proton is subatomic particle which is present inside nucleus of an atom.

ANS: Name of element is Lithium (Li) as it’s atomic number is Z=3.
Distribution of electrons in Li (Z = 3) = 2,1
(Concept: If the number of electrons in the outermost shell of the atom of an element is less than or equal to 4, then the valency of the element is equal to the number of electrons in the outermost shell.)
Since, outermost shell have 1 electrons so,The valency of Lithium = 1

ANS: Mass number of an atom = Number of protons + Number of neutrons
Mass number of X = 6 + 6 = 12 Carbon
Mass number of Y = 6 + 8 = 14 Carbon
Since, atomic number (same protons) of X and Y is same but their mass numbers are different so both are Isotopes.

(a) J.J. Thomson proposed that the nucleus of an atom contains only nucleons.(F)
(b) A neutron is formed by an electron and a proton combining together. Therefore, it is neutral. (F)
(c) The mass of an electron is about 1/2000 times that of proton. (T)
(d) An isotope of iodine is used for making tincture iodine, which is used as a medicine. (T)

ANS:(a) Atomic Nucleus (☑)
(b) Electron(☒)
(c) Proton(☒)
(d) Neutron (☒)

ANS: (a) the same physical properties (☒)
(b) different chemical properties (☒)
(c) different number of neutrons(☑)
(d) different atomic numbers. (☒)

ANS: (a) 16 ☒
(b) 8 (☑)
(c) 17 ☒
(d) 18 ☒

ANS: (a) 2,8 (☒)
(b) 8,2,1 (☒)
(c) 2,1,8 (☒)
(d) 2,8,1 (☑)

ANS: