What is atom?

An atom is the basic particle of the chemical elements that consists of a nucleus surrounded by electrons in one or more orbit (Depending on the number of electrons in that atom). Nucleus consists of protons and neutrons. There are 118 known elements in the universe, among those only the first 92 exist naturally on Earth and all other elements are the product of nuclear fission.

An element is a fundamental thing that can’t be easily broken into smaller pieces. Example- Hydrogen, Helium, Carbon, Oxygen, Sodium, Chlorine etc. The basic particle of the element is atom. Atom can not exist independently except the inert gas (It is also called noble gas). Noble gas element exist as mono-atoms in molecules.

Number of protons in an atom is called it’s atomic number. With the change of atomic number, name and property of elements are changed.

Atoms are extremely small, typically around 100 picometers (10⁻¹²). More than 99.94% of the mass of an atoms is in the nucleus.

The electrons have a negative electric charge, the protons have a positive electric charge and the neutrons have no electric charge. If the number of protons and electrons are equal, then the atom is neutral. If an atom don’t have same number of proton and electron, then it has an overall negative or positive charge, such charged such atoms are called ions.

What is molecule?

A molecule is the smallest particle of a pure substance which can exist independently. It can be divided but chemical properties of the components (Atoms) stay as it is. Atoms are bonded together to form smallest fundamental unit of a chemical compound that can exist independently.

A molecule may be homonuclear ( it consists of atoms of one chemical element) e.g. two atoms in the oxygen molecule (O₂); or it may be heteronuclear, a chemical compound composed of different atoms e.g. water ((H₂O) which is formed with the 2 atoms of hydrogen and 1 atom of oxygen.

What is the difference between atom and molecule?

	Atoms	Molecules
1	Atoms are the smallest particles of an element that can take part in a chemical reaction	Molecules rea the smallest part of an element or compound that can exist independently
2	Atoms may or may not exist independently	Molecules exist independently
3	Atoms don’t break during chemical reactions	Molecules break during chemical reactions
4	Atoms are formed by protons, neutrons and electrons	Molecules are formed by two or more atoms by covalent or ionic bonds
5	Examples of atoms are Hydrogen, Carbon, Oxygen, Sodium	Examples of molecules are Water (H2O), Carbon dioxide (CO2)