Atomic Theory Scientist Cards

Name:

Date:

🧪 Scientist Information Cards

Instructions: Cut out these cards and use them to create your atomic theory timeline. Read each card carefully and discuss the contributions with your group.

DEMOCRITUS

Date: 460-370 BCE (Ancient Greece)

Contribution: First person to propose that all matter is made of tiny, indivisible particles called "atoms" (meaning "uncuttable" in Greek). He believed atoms were solid, had different shapes and sizes, and moved in empty space. His ideas were based on philosophical thinking, not experiments.

Key Idea: Everything is made of atoms that cannot be divided further.

JOHN DALTON

Date: 1803

Contribution: Created the first scientific atomic theory based on experimental evidence. He proposed that atoms of the same element are identical, atoms of different elements have different masses, and atoms combine in simple ratios to form compounds.

Key Idea: Atoms are like tiny, solid spheres that cannot be created or destroyed.

J.J. THOMSON

Date: 1897

Contribution: Discovered the electron through cathode ray tube experiments. He proved that atoms contain smaller particles and proposed the "plum pudding" model - atoms as positive spheres with negative electrons embedded inside like raisins in a pudding.

Key Idea: Atoms are not solid spheres but contain smaller charged particles called electrons.

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ERNEST RUTHERFORD

Date: 1911

Contribution: Conducted the gold foil experiment which showed that atoms have a tiny, dense, positive centre called the nucleus. Most of the atom is empty space with electrons moving around the nucleus. This disproved Thomson's plum pudding model.

Key Idea: Atoms have a small, dense nucleus at the centre with electrons orbiting around it.

NIELS BOHR

Date: 1913

Contribution: Improved Rutherford's model by proposing that electrons orbit the nucleus in specific energy levels or "shells." Electrons can jump between these levels by absorbing or releasing energy. This explained why atoms are stable and don't collapse.

Key Idea: Electrons orbit the nucleus in fixed energy levels, like planets orbiting the sun.