Atomic theories

Question 1

Democritus (460-370 BC)

Answer 1

a greek philosopher who was first to propose the idea that atoms exist. Atomos means not to be cut or indivisible

Question 2

Dalton (1803)

Answer 2

Each element composed of atoms. Atoms are neither created nor destroyed. Atoms of different elements are different

Question 3

J. J. Thomson (1897)

Answer 3

used a cathode ray tube and identified the mass of an electron and its charge, plum pudding model of the atom. As the current passed through the gas it gave off rays of negatively charged particles. He determined they were negatively charged because they attracted the positive particles

Question 4

Ernest Rutherford (1907)

Answer 4

Gold foil experiment. Fired positively charged particles at the thin gold sheet. Most of the positively charged particles passed right through the gold atoms without changing course. Few of the protons bounce back or were deflected from a straight path

Question 5

Nieles Bohr (1913)

Answer 5

Nucleus surrounded by orbiting electrons in specific energy levels.