# ATOM, ORBITS AND ENERGY LEVELS

In this we will learn about Atom, Orbits and Energy Levels depending upon number of electrons.

## ATOM

Atom is the smallest unit of matter. An atom composed of three subatomic particles that are electron, proton and neutron. The neutrons and the protons make the center of an atom called nucleus. And the electrons moves around the nucleus in orbits (shell).

Electrons are negatively charged particles, Protons are positive charged particles &Neutron is neutral means no charge is present

Electrons  “–”

Protons  “+”

Neutron  “ ”

Things to be note:

• As we know nucleus composed of proton and neutron, and protons are positively charged and neutron has no charge so overall we can say nucleus is positively charge.
• The strong nuclear force between neutrons and protons stick them together to form a nucleus.
• The negatively charged electrons are orbiting around the nucleus because of the electrostatic force of attraction present between electrons and protons.

If the numbers of electrons are equal to number of protons in an atom then the overall charge of atom is neutral.

And if the numbers of electron are more than the numbers of protons in an atom then the atom is negatively charged.

If the numbers of electron are less than the numbers of protons in an atom then the atom is positively charged.

The charge of proton and electron measures in coulombs, denoted by “C”.

Charge of a electron = – 1.602 × 10-19 Coulombs (C)

Charge of a proton = + 1.602 × 10-19 Coulombs (C).

Both the charges are equal in magnitude but have different signs.

## ORBITS AND ENERGY LEVEL

Orbits (shells) are the energy levels of atoms in which electrons moves around the nucleus. Energy of electrons in 1st orbit is less than energy of electrons in 2nd orbit. Similarly, energy of electrons in 2nd orbit is less than that of 3nd orbit.

In other words, energy of electrons in inner orbits has less energy compared to outer orbits. Energy orbit N is greater than orbit N-1. • Maximum 2 electrons in 1st shell can be present
• While, Maximum 8 electrons in 2nd shell can be present
• However, Maximum of 18 electrons in 3rd shell can be present

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