# Knowledge Base

Most Useful Content for Parents, Teachers & Students

### What are Atoms?

Atoms are the tiny building blocks of matter. All the things on the earth are made up of a combination of atoms. Atoms are made up of electrons, protons, and neutrons. Protons and neutrons are at the center of the atom because they are heavier than an electron. Center of the atom is known as the nucleus.

Atoms are made up of small particles, known as photons. Protons are positively charged. Other small particles are neutrons, which have no charge and also have the other small particles known as electrons and electrons are negatively charged.

Who discovered the atom and when?

Ernest Rutherford discovered the atoms in 1911.He performed many experiments to explore radioactivity.

Conclusion is drawn by Rutherford

• Rutherford concluded from the alpha particles scattering experiment that-
1. The space inside the atom is empty, because of the alpha particles. Most of the alpha particles pass through the gold foil and do not get deflected.
2. Some of the particles get deflected from their path. Particles get deflected because positive charge of atoms occupies very little space.
3. Very small alpha particles were deflected by 180 °C. It indicates that all the positive charges and the mass of gold atom were concentrated in very small volume in the atom.

### Bohr Model

Niels Bohr improved the model of atoms in 1913. He placed each electron in a specific energy level.

According to Niels Bohr atomic model, the electrons moves in definite orbits around the nucleus, as like the planets around the sun. These orbits are located at the certain distances from the nucleus.

Bohr model of an atom   says that each orbit can hold the specific maximum number of electrons

Shell               maximum no. of electrons

1. K                   2
2. L                   8
3. M                18
4. N                 32

### Atomic Structure

The number of protons in the nucleus of an atom, which helps to tell the characteristics of the element also determine the where the element lies in the periodic table.

### Atomic mass

The number of are electrons equal to the number of protons, which expressed in the atomic mass unit.

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