Atomic Structure: Electron, Proton, Neutron etc.

Atomic Structure: Electron, Proton, Neutron etc.

Atom:

The smallest particle of an element is called an atom. An atom can take part in chemical combination and does not occur free in nature. The atom of the hydrogen is the smallest and lightest. Example – Na, K, Ca, H etc.

Molecule: A molecule is the smallest particle of an element or compound that can have a stable and independent existence. Example – O₂, N₂, Cl₂, S_s etc.

Mole: A mole is a collection of 6.023 x 10²³ particles. It means that

1 mole = 6.023 x 10²³

1 mole atom = 6.023 x 10²³ atoms

1 mole molecule = 6.023 x 10²³ molecules

1 mole ion = 6.023 x 10²³ ions

1 mole mango = 6.023 x 10²³ mangoes

1 mole apple = 6.023 x 10²³ apples

Avogadro’s number: The number 6.023 x 10²³ is called Avogadro’s number.

Atomic Mass: It is the ratio of mass of one atom of the element to th part of the mass of one atom of carbon – 12.

Actual mass of 1 atom of an element = atomic mass in amu x 1.66 x 10^-24g

Molecular mass: It indicates how many times one molecule of a substance is heavier in comparison to th mass of one atom of Carbon-12.

Constituents of an atom:

Fundamental particles of an atom are Electron, Proton & Neutron.

Electron:

 (i) Electron had been discovered by J.J. Thomson.

(ii) The name of electron was given by Stoney.

(iii) Charge and Mass of Electron –

(iv) 

 ratio of electron = – 1.79 x 10⁸ 

(v) An electron was obtained from Cathode rays experimental.

Proton:

(i) A proton had been discovered by Goldstein.

(ii) A proton was named by Rutherford.

(iii) Charge and mass of proton –

(iv) 

 ratio for proton = 9.58 x 10⁴ 

(v) An proton was obtained from anode rays experiment.

Neutron:

(i) A neutron had been discovered by James Chadwick.

(ii) Charge and mass of Neutron –

(iii)  ratio of neutron = ZeroA neutron was obtained from radioactivity phenomenon.

(iv) A neutron was obtained from radioactivity phenomenon.

Atomic number (Z): The number of proton or electron in an atom of the element is called atomic number. It is denoted by Z.

Mass Number (A): The sum of number or protons and neutron in an atom of the element is called mass number. It is denoted by A.

A = p + n where, p = no. of proton and n = no. of neutron Let,  Na,

In Na, Z = 11, A = 23 and,
e = 11, p = 11,
n = A – p = 23 – 11 = 12

Isotopes: These are atoms of the elements having the same atomic number but different mass number.

Isobars: These are atoms of the elements having the same mass number but different atomic numbers. e.g.

Isoelectronic: These are atoms / molecules / ions containing the same number of electrons.
(i) O^2–, F^–, Ne, Na⁺, Mg²⁺       (ii) CN^–, N₂ etc.

Thomson’s model of an atom:

According to Thomson, an atom is treated as sphere of radius 10^–8 cm in which positively charged particles are uninformally distributed and negatively charged electrons and embedded through them. This is also called Plum-Pudding model of an atom or water-melon model of an atom.

Rutherford’s model of an atom:

On the basis of scattering experiment, Rutherford proposed a model of the atom which is known as nuclear atomic model.

According to this model,

(i) An atom consists of a heavy positively charged nucleus where all protons and neutrons are present. Protons & neutrons are collectively called nucleons. Almost whole mass of the atom is contributed by these nucleons.

(ii)        Radius of a nucleus = 10^–13 cm
            Radius of an atom = 10^–8 cm

            Radius of an atom = 10⁵ times of the radius of the nucleons.

So, volume of an atom is 10¹⁵ times heavier than volume of a nucleus.

(iv) Electrons revolve around the nucleus in closed orbits with high speed. This model is similar to the solar system, the nucleus representing the sun and revolving electrons as planets. The electrons are therefore, generally referred as planetary electrons.

Spectrum:

When white light is allowed to pass through a prism, it splits into several colours. These seven coloured band is called spectrum.

Zeeman's effect:

When spectral lines obtained from atomic spectra is placed in a magnetic field, they are splitted into number of fine lines, this is called Zeeman's effect.

Stark's effect:

When spectral lines obtained from atomic spectra is placed in electric field, they are splitted into number of fine lines this is called Stark's effect.

Thomson's model: Plum pudding model (watermelon model)

Rutherford's model: Nuclear theory

Bohr's model: Concept of Quantization of energy.

Plank's Quantum theory: Photon & quanta.

Sommerfeld's model: Orbital-elliptical & spherical

de-Broglie's equation: Dual nature of electron

Heisenberg's Uncertainty principle: Exact position & momentum cannot be determined simultaneously

Schrodinger's wave equation: wave nature of electron.