What You Need to Know

Key Concept Diagram

Dalton (1803): atoms are solid, indivisible spheres like billiard balls

Thomson (1904): plum pudding model - electrons embedded in positive charge

Rutherford (1911): nuclear model - tiny dense nucleus with electrons orbiting around it

Bohr (1913): electrons occupy specific energy levels (shells) around the nucleus

Key Vocabulary

Atom

The smallest particle of an element that retains its chemical properties

Electron

A subatomic particle with negative charge that orbits the nucleus

Nucleus

The dense central core of an atom containing protons and neutrons

Proton

A positively charged subatomic particle found in the nucleus

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

Rutherford's gold foil experiment disproved the plum pudding model by showing:

Atoms are indivisible spheres Most of the atom is empty space with a tiny, dense, positive nucleus Electrons have negative charge Atoms contain neutrons

Question 2

In Bohr's atomic model, electrons:

Are scattered randomly throughout the atom Are embedded in a positively charged cloud Occupy specific energy levels (shells) at fixed distances from the nucleus Are not present in the atom

Question 3

Why is the history of atomic models important in science?

Because older models are always correct To show that science never changes Because Dalton's model is still used today It shows how scientific understanding evolves as new evidence challenges existing models

History of Atomic Models