When you hear the word “atom,” what comes to your mind? Tiny balls? Circles with electrons flying around? Let’s make it clearer than ever!
An atom is the smallest unit of matter that keeps the properties of an element.
Every element in the Periodic Table is made of atoms. So when you touch water, salt or even your phone — you are touching atoms!
Table of Contents
PARTS OF AN ATOM
Each atom is made of three basic subatomic particles:
| Particle | Charge | Location | Mass |
| Proton (p⁺) | Positive (+1) | Inside the nucleus | 1 amu |
| Neutron (n⁰) | Neutral (0) | Inside the nucleus | 1 amu |
| Electron (e⁻) | Negative (−1) | Outside nucleus (in shells) | Almost 0 amu |
THE NUCLEUS – THE ATOM’S BRAIN
The nucleus is the tiny center of the atom. It contains:
- Protons (positive)
- Neutrons (neutral)
It’s very dense and holds most of the atom’s mass
Electron Shells – Where Electrons Live
Electrons are very tiny and move in energy levels (also called shells or orbits) around the nucleus.
Electrons are responsible for chemical reactions and bonding.
IMPORTANT ATOMIC TERMS TO KNOW
Let’s break down some key terms every student must understand:
1. Atomic Number (Z)
- Tells you the number of protons in an atom
- It also equals the number of electrons (in a neutral atom)
Example: Carbon has atomic number 6 → 6 protons and 6 electrons
2. Mass Number (A)
- Mass number = Protons + Neutrons
- It tells you the total mass of the nucleus
Example: Oxygen has 8 protons and 8 neutrons → Mass number = 16
3. Isotopes
Atoms of the same element with the same number of protons, but different numbers of neutrons.
Example:
- Carbon-12 and Carbon-14 are both carbon
- But Carbon-14 has 2 extra neutrons
Isotopes are useful in medicine and dating fossils!
4. Ions
Atoms that have gained or lost electrons.
- If it loses electrons → becomes positive (cation)
- If it gains electrons → becomes negative (anion)
Example:
- Na → Na⁺ (lost 1 electron)
- Cl → Cl⁻ (gained 1 electron)
BORH’S MODEL – A SIMPLE ATOM PICTURE
Bohr’s model shows electrons in circular shells around the nucleus.
| Shell | Max Electrons |
| 1st (K) | 2 |
| 2nd (L) | 8 |
| 3rd (M) | 18 |
| 4th (N) | 32 |
Electrons fill from lower to higher energy levels. This filling pattern is important in bonding!
RECAP
- Atoms are the building blocks of everything
- Made of protons, neutrons, and electrons
- Atomic number = number of protons
- Mass number = protons + neutrons
- Isotopes = same element, different mass
- Ions = atoms that gained or lost electrons
- Electrons live in shells and take part in bonding
Read Also: The History Of Atomic Theory (A Fundamental Approach)
