Atomic Structure

Atoms are made of three different sub atomic-particles:

Protons (p)

Neutrons (n)

Electrons (e)

Protons and neutrons are known as nucleons, as they are tightly packed together at the centre of the atom, forming the nucleus. Electrons move rapidly around the nucleus. 

Protons:

- Carries one positive electric charge (+1)

- Has a relative mass symbol of 1 

Neutrons

- Carries no electric charge

- Has a relative mass of 1

Electrons:

- Carries one negative electric charge (-1)

- Has a relative mass of 1/1840 (negligible)

All atoms are electrically neutral. An atom contains an equal number of positively charged protons and negatively charged electrons. They cancel out exactly.

The number of protons in a number is called the proton number or the atomic number. The atomic number is represented by the symbol Z. Also, the atomic number shows how many electrons are in an atom too. 

The total number of protons and neutrons in an atom is called the nucleon number or the mass number. The mass number is represented by the symbol A. The mass of an atom depends on the number of protons and nucleons in the atom's nucleus. The mass of an electron is negligible.

The atomic and mass numbers can be included when representing an element in symbols. The atomic number is in subscript (below), left of the symbol. The mass number is in superscript (above), left of the symbol. For convenience, the element can be represented using only the mass number. E.g.: Sodium-23 or ²³Na. 

Nucleon number > No. of protons and neutrons (relative atomic mass)

Atomic number > No. of protons/ No. of electrons

Ions > Formed when e-s are lost/ gained