Maharshi Kanad (600 BC)
- He said that matter is made up of very small particles.
- They called it 'Parmanu'/'परमाणु'.
- The theory was proposed in 430 BC.
- He said that all matter is made up of very small particles.
- He called that particle 'atoms'.
- In 1808, he proposed his theory.
- All matter is made up of small particles, called atoms.
- An atom cannot be created or destroyed.
Drawback: According to these three theories, it is not possible to say about the charge and particle in an atom.
J. J. Thomson
- In 1867, he proposed his model of an atom.
- He discovered the inner particle of an atom.
- He compared an atom to a watermelon. Where he considered: 1. The red part of the watermelon as positively charged. 2. Watermelon seeds as negatively charged particles, embedded in them.
- He said that an atom resembles a sphere of positive charge with electrons (negatively charged particles) present inside the sphere.
Drawback: Positive charge is scattered all over the atom and negative charge is scattered in it. Thomson was wrong to say this.
- In 1911, he proposed his theory.
- He compared an atom to a solar system. In it, the sun is the nucleus and the planet is the election.
- An atom is hollow.
- The midpoint of an atom is called the nucleus.
- All the mass of the atom is contained in the nucleus.
- Electrons move in a circular path outside the nucleus.
Drawback: Rutherford could not say that the electron rotates in a certain orbit.
- Discovered by Rutherford.
- Atoms contain protons and neutrons.
- Orbits contain electrons and positrons.
- The number of protons or electrons in an atom is called the atomic number.
- Atomic numbers are denoted by the letter 'Z'.
- g. A carbon atom has 6 protons and 6 electrons. So the atomic number (Z) of carbon is 6.
Atomic mass number
- The complete amount in the protons and neutrons in the nucleus of an atom.
- Atoms contain particles like Protons, Neutrons & Electrons. But since the mass of the electron is very small, only the mass of the protons and the neutrons are taken into account while measuring the mass of the atom.
- The combined number of protons and neutrons in an atom is the atomic mass.
- Molecules are denoted by the letter 'A'.
Atomic Mass (A) = atomic number (Z) + n
Neutron = Atomic Mass (A) - Atomic Number (Z)
- E.g. The atom of carbon has 6 protons and 6 neutrons, so the atomic mass (A) of carbon is 6 + 6 = 12.
- Molecular mass is the sum of the aggregate masses of atoms in a molecule.
- Note: The hydrogen atom has 1 proton & 0 neutrons, so H has a molecular mass of 1.
- He said that electrons move in a fixed orbit, with a certain energy, at a certain speed.
- There is a hollow space between the two chambers, the electron only found in orbit.
- He named these shells K, L, M, N in ascending order of energy level.
- The ability to accommodate electrons in each shell is different and specific.
- Formula to fill the electron in the orbit:2n^2
- Shell = (n = Orbit number)
K=2X(1)^2 = 2
L=2X(2)^2 = 8
M=2X(3)^2 = 18
N=2X(4)^2 = 38
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