History of Chemistry

Overview of important discoveries made by scientific figures

Antoine Lavoisier (1743-1794)

he weighed the reactants and products of various combustion experiments, discovering the law of conservation of mass

mass is neither created nor destroyed

what is the law of conservation of mass?

Proust

he discovered that a given compound always contained exactly the same proportion of elements by mass, known as the law of definite proportions

Dalton

he discovered the law of multiple proportions

when 2 elements form a series of compounds, the ratios of the masses of the second element that combine with 1 gram of the first element can always be reduced to small whole numbers

what is the law of multiple proportions?

Dalton’s Atomic Theory (1808)

1. Elements are made up of tiny particles known as atoms.

2. The atoms of a given element are identical. The atoms of different elements are different in some fundamental ways.

3. Compounds are formed when atoms combine with one another in a specific way.

4. Chemical reactions involve reorganization of the atoms. The atoms themselves are not changed.

Joseph Gay-Lussac (1778-1850)

he measured volumes of gases reacting under the same temperature & pressure, and discovered that they combine in simple whole-number ratios; known as the law of combining volumes

Amedeo Avogadro (1776-1850)

in 1811, he proposed that equal volumes of gases at the same temperature and pressure contain the same number of particles; helped explain why gases with different properties still followed Gay-Lussac’s simple volume ratios

J.J. Thomson (1856-1940)

in 1897, he used a cathode ray tube to show that atoms contain tiny negatively charged particles (electrons); the rays in the tube were deflected by electric and magnetic fields, proving the particles had mass and charge, which revealed that atoms are divisible

Robert Millikan (1868-1953)

he created the oil drop experiment that utilized oil droplets, a microscope, electrically charged plates, and x rays to produce charges on the drops; discovered that electrons have a negative charge

radioactivity

coined by Marie Curie and has three types of emission:

1. alpha particles

2. beta particles

3. gamma rays

alpha particles

2+ charge and mass » than electrons

beta particles

high speed electrons; negatively charged particles

gamma rays

high-energy light

Ernest Rutherford (1871-1937)

he performed the gold foil experiment (1911), firing alpha particles at thin gold foil; most particles passed through, but some were deflected at large angles this showed that atoms have a tiny, dense, positively charged nucleus at the center, with electrons surrounding it, leading to the nuclear model of the atom