Chemistry atoms and periodic table history

Democritus (460-370 BC)

first to propose that matter wasn’t infinitely divisible.

matter made of atomos

atoms moved through empty space

atoms were solid and couldn’t be created or destroyed or further divided

Aristotle (384-322 BC)

rejected the atom idea because it didn’t align with his views of nature.

Didn’t believe in empty space

influenced the rejection of democritus’ ideas.

John Dalton (1766-1844)

Atomic theory -

matter is made of atoms

cannot be broken or divided

atoms of an element are all identical

solid ball model of an atom

JJ Thompson (1856-1940)

discovered the electron

proposed plum pudding model

cathode-ray tube

proposed charged jelly that held negative charge

Ernest Rutherford (1871-1937)

gold foil experiment

existence of nucleus

determined that the atom consisted mostly of empty space

mass of the atom was contained in the center (nucleus)

also discovered the proton

Niels Bohr (1885-1962)

discovered that electrons ‘orbit’ around the nucleus

Bohr Ring Model/solar system model

Erwin Schrodinger (1887-1961)

developed the idea that electrons are found in a cloud around nucleus and move in waves.

Werner Heisenberg (1901-1976)

uncertainty principle - cannot determine the speed and position of the electrons around the nucleus.

led to development of quantum mechanics and theory of specific electron orbitals

James Chadwick

proposed that the nucleus also has a neutral partial neutron.

electron

mass - less than 1

location - space around nucleus

charge - negative

proton

mass - 1

location - nucleus

charge - positive

neutron

mass - 1

location - nucleus

charge - neutral

dobereiner

arranged periodic table by properties

Dobereiner’s Triads

Dmitri Mendelev

arranged first periodic table

Henry Moseley

discovered that atomic numbers showed protons and have a strong physical basis. Created the periodic table we know today