Atomic Structure
Atomic structure means how an atom is built inside.
Every atom has a nucleus in the centre and electrons moving around it.
Inside the nucleus are protons (positively charged) and neutrons (no charge).
The electrons move around the nucleus in specific paths called shells or orbits.
So the atomic structure shows how protons, neutrons, and electrons are arranged inside an atom.
Proton
A proton is a tiny particle found inside the nucleus.
It has a positive charge (+1) and gives the atom its identity.
The number of protons decides which element it is.
For example, 1 proton = hydrogen, 6 protons = carbon, 8 protons = oxygen.
Protons also add to the atom’s mass.
Neutron
A neutron is also found inside the nucleus.
It has no charge (neutral) but has almost the same mass as a proton.
Neutrons help keep the nucleus stable and also add to the atomic mass.
Electron
An electron is a tiny particle that moves around the nucleus in shells.
It has a negative charge (–1) and almost no mass.
Electrons move very fast and are responsible for the chemical reactions of atoms.
The outermost electrons decide how an atom bonds with others.
Positive Charge
Positive charge means the atom or particle has more protons than electrons.
Protons give positive charge because each proton carries a +1 charge.
When an atom loses electrons, it becomes positively charged (a positive ion).
Negative Charge
Negative charge means the atom or particle has more electrons than protons.
Electrons give negative charge because each carries a –1 charge.
When an atom gains electrons, it becomes negatively charged (a negative ion).
Shells and Orbits
Shells (or orbits) are the circular paths where electrons move around the nucleus.
Each shell can hold only a fixed number of electrons:
1st shell → 2 electrons
2nd shell → 8 electrons
3rd shell → 8 electrons (for your level)
Electrons fill the shells in order, starting from the one closest to the nucleus.
Electronic Structure / Arrangement of Electrons
Electronic structure means how the electrons are arranged in shells around the nucleus.
This arrangement is written in numbers showing how many electrons are in each shell.
Example:
Hydrogen → 1
Carbon → 2,4
Oxygen → 2,6
Sodium → 2,8,1
The last shell’s electrons are called valence electrons, and they decide how the atom reacts in chemical reactions.
Atomic Number
The atomic number tells how many protons are in the nucleus of an atom.
It is unique for every element and acts like its identity number.
Because atoms are neutral, the number of protons also equals the number of electrons.
Example: Carbon’s atomic number is 6, so it has 6 protons and 6 electrons.
Atomic Mass
Atomic mass tells how heavy an atom is.
Almost all the mass of an atom comes from protons and neutrons because electrons are extremely light.