Atomic and Nuclear Physics · 8 min read
Models of the atom
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Introduction to the atom
Everything you see, from the garri you eat to the generator in your backyard, is made of tiny building blocks called atoms. For a long time, scientists tried to figure out what the inside of an atom looks like. They created different models to explain it, just like how a mechanic might explain the parts of an engine.
The Dalton model
John Dalton started it all. He thought the atom was like a solid marble or a small ball that could not be broken into smaller pieces. He believed atoms were the smallest things in the world.
Essentially, Dalton saw the atom as a hard, solid ball that could not be split.
The Thompson model
J.J. Thompson discovered electrons and realized Dalton was wrong. He described the atom like a plum pudding or a bowl of pap with honey beans inside. The beans (electrons) are scattered inside a positive 'soup'.
This means the atom is a positive ball with negative particles stuck inside it.
The Rutherford model
Ernest Rutherford did a famous experiment by firing alpha particles at a thin gold foil. He found that most of the atom is actually empty space, with a tiny, heavy center called the nucleus.
This model tells us that the center of the atom is very heavy and positive, while the rest is mostly empty.
The Bohr model
Neils Bohr improved on Rutherford's idea. He said electrons do not just float around; they move in specific paths called energy levels or shells, just like an okada must stay on its lane on a busy road.
In simple terms, electrons stay in their own special paths and do not just crash into the center.
The electron cloud model
Modern scientists now say we cannot be 100% sure where an electron is. Instead of neat circles, electrons exist in a 'cloud' or a region of high probability around the nucleus.
Example calculation on atomic mass
An atom has a mass number of 23 and an atomic number of 11. Calculate the number of neutrons in this atom.
1. Use the formula: Mass Number (A) = Number of Protons (Z) + Number of Neutrons (N).
2. We know A = 23 and Z = 11.
3. Rearrange the formula: N = A - Z.
4. Calculate: 23 - 11 = 12.
5. The atom has 12 neutrons.
Key points
- •Dalton thought the atom was an indivisible solid sphere.
- •Thompson discovered the electron and proposed the plum pudding model.
- •Rutherford discovered the nucleus through the gold foil experiment.
- •Bohr proposed that electrons move in fixed energy orbits.
- •The nucleus contains protons and neutrons, while electrons orbit outside.