History Of The Atom

Question 1

Democritus 500BC

Answer 1

Small spheres, separated by empty space, smallest possible unit of matter ====> atomic theory

Question 2

John Dalton early 1800s

Answer 2

Solid spheres, different kinds of spheres made up the different elements

Question 3

J.J Thompson 1897

Answer 3

Plum pudding model - atom is a ball of positive charge with electrons randomly stuck in it

Question 4

Ernest Rutherford 1909

Answer 4

Nuclear model - fired alpha particles at an extremely thin gold sheet. They expected the particles to pass straight through the sheet as it was said that the positive charge was spread out (plum pudding model).however, Some particles were deflected backwards. ❌ plum pudding model. Nuclear model - positively charged nucleus where most of the mass is concentrated. A cloud of negative electrons surrounds this nucleus. Most of atom is empty space. When alpha particles were fired at nucleus, they deflected backwards.

Question 5

Niels Bohr’s Nuclear model 1913

Answer 5

Rutherford ❌ otherwise atom would collapse. Bohr said that electrons orbit the nucleus in fixed shells. Each shell is a fixed distance from the nucleus

Question 6

Rutherford 2.0

Answer 6

Positive charge is made up from protons. Discovery of protons

Question 7

James Chadwick

Answer 7

Discovery of neutrons. Nuclear model complete