Atomic History I

Question 1

Democritus (400 B.C.)

Answer 1

. Proposed that matter was composed of tiny indivisible particles.

Question 2

Lavoisier (1777)

Answer 2

. French chemist considered founder of modern chemistry
. Clarified concept of an element as a simple substance that could not be broken down by any known method of chemical analysis.
. He published the law of conservation of mass- mass is neither created nor destroyed during ordinary chemical reactions or physical changes.

Question 3

Proust (1794)

Answer 3

. Published the law of definite proportions.
. Law states that the ratio of elements in a compound is always the same.

Question 4

John Dalton (1808)

Answer 4

. Dalton adds his own - the law of multiple propositions.
. Proposed a theory to summarize and explain these three laws.
. Law of multiple propositions: Two or more elements can combine to form different compounds in a whole-number ratios.

Question 5

Daltons Four postulates

Answer 5

1. Elements are composed of small indivisible particles called atoms.
2. Atoms of the same element are identical. Atoms of different elements are different.
3. Atoms of different elements combine together in simple whole-number ratios to create a compound.
4. In a chemical reaction, atoms are rearranged but not changed.