History of The Periodic Table

* school science

[2026-01-21 Wed]

1. Democritus said that matter is made of 'atoms'

Proposed:
- Atoms come in different sizes
- Atoms cannot be cut
- Atoms have space between them

2. Aristotle Disagreed

Disagreed with Democritus
Believed that everything was made from four elements: earth, water, air, and fire
His ideas were accepted for many years

3. John Dalton

John Dalton proposed the billiards model. All atoms were spheres.

4. JJ Thompson

JJ thompson proposed the plum pudding model:

Atoms have positive and negative charges
He passed an electric current between two oppositely charged plates in a circuit. He observed that the negative particles were attracted to the positive ones

4.1. Cathode Ray Experiment

Thomson used a cathode ray tube (a sealed glass tube with most of the air removed)

An electric current was passed between a negative cathode and a positive anode
A beam called a cathode ray traveled from the cathode to the anode

4.1.1. Observations

The cathode ray was attracted to the positive plate
The ray was repelled by the negative plate
This showed the ray was made of negatively charged particles

4.1.2. Conclusions

Atoms contain small, negatively charged particles called electrons
Since atoms are neutral overall, there must also be positive charge in the atom
This led to the plum pudding model, where electrons are embedded in a positively charged sphere

5. Ernest Furtherford

Rutherford shot particles through a gold foil. Most passed through, but some bounced back. This was how he disocvered there was a nucleus with positively charged particles