Unit 3 Atomic Theory

Question 1

Democritus

Answer 1

400 BC
A Greek philosopher
First person to think about an atom’s existence.
Believed that matter was composed of tiny indivisible particles (building blocks) called atoms.
He had no experimental evidence to support his thoughts.

Question 2

Aristotle

Answer 2

350 BC
A Greek philosopher
Believed that matter was infinitely divisible
He thought that the matter was made of 4 elements called earth, water, air, and fire.

Question 3

Dalton

Answer 3

1803
An English chemist and meteorologist
By using experimental methods, he transformed Democritus’s ideas on atoms into a scientific theory made of 4 ideas
1: All elements are composed of tiny indivisible particles called atoms
2: Atoms of the same element are identical. Atoms of any one element are different from those of any other element.
3: Atoms of different elements can physically mix together or can chemically combine in whole number ratios to form compounds.
4: Chemical reactions occur when atoms are separated, combined, or rearranged. Atoms off one element are not changed into atoms of another element as a result of a chemical reaction.