Chemistry - History of Atoms

Democritus

• Greek philosopher

• Believed matter was made up of tiny particles called atoms

• Stated the atom was the smallest particle and could not be divided

• Different sizes and shapes of different atoms

John Dalton

• Performed multiple experiments, studied chemical reactions and determined mass ratios to help support his theory.

• Several ideas in Daltons Atomic Theory

• 1. Matter is composed of extremely small particles called atoms

• 2. Atoms are indivisible - FALSE

• 3. Atoms of a given element are identical in size, mass, and chemical properties - FALSE

• 4. Atoms of different elements are different from those of other elemtns

• Different atoms combine to form compounds

• atoms are separated, combined or rearranged in chemical reactions.

JJ Thompson

• performed a series of experiments with cathode rays (negatively charged stream of particles)

• desired to determine the ratio of its charge to its mass

• discovered the first subatomic particle - the electron

• proposed the plum pudding model

Ernest Rutherford

• Gold Foil: expected the alpha particles to go through the gold foil but saw the particles get deflected at large angles.

• atoms positive charge was located in a small, dense area called the nucleus.

• positively charged atoms were called protons.

• suggested most of the atom consisted of empty space.

James Chadwick

• Rutherfords co-worker

• discovered the nucleus also contained a neutron - a subatomic particle that has no charge but the same mass as the proton

Niels Bohr

• proposed that electrons were found in shells

• won the noble prize for studies of electron arrangement

• determined electron arrangements importance in chemistry

Heisenberg

• Electron can act as a wave

• Electron can act as a particle

• The position of an electron cannot be exactly determined