Chemistry Atomic Theory

1800-1820

Gases react in simple volume ratios (Dalton)

1879

Electric discharges in gas investigated (Crookes)

1896

Radioactivity discovered (Becquerel)

1897

Cathode ray experiments (Thomson)

1901-1920

Positive beam experiments (Thomson)

1909

Oil drop experiment (Millikan), Gold foil experiment (Rutherford)

1932

Produced neutrally charged subatomic particles (Joliot-Curie), Identified neutron (Chadwick)

Who was John Dalton?

English schoolteacher, claimed the atom was the smallest particle of matter

Dalton's Atomic Theory

1) All matter is made of atoms. Atoms are indivisible and indestructible.

2) All atoms of a given element are identical in mass and properties

3) Atoms of different elements combine in specific ratios to form compounds

4) In a chemical reaction, atoms are separated, rearranged, and recombined to form new compounds

Who was William Crookes?

English scientist from the 19th century who investigated the nature of electrical discharge in gas

What did Crookes experiment with?

He experimented with glass tubes that contained gas at low pressures, these tubes had both a positive electrode (anode) and a negative electrode (cathode) implanted - The first cathode ray tube

What did William Crookes discover?

he observed the shadow the cathode beam cast and concluded that atoms contain negatively charged particles

Who was JJ Thomson?

He was an English scientist who duplicated Crookes' experiment with CRT which lead him to the discovery of the electron

What was JJ Thomsons model of the atom?

Plum pudding model: negative electrons embedded in a positively charged sphere

What awards did JJ Thomson receive?

He was awarded the Nobel prize for his discovery in 1906

Who was Robert Millikan?

He was an American physicist who was able to determine the mass and charge of an electron through his oil drop experiment.

Who was Henry Becquerel?

French scientist who discovered radioactivity through experimenting with black paper and uranium

Who was Ernest Rutherford?

New Zealand scientist, discovered two of the three radioactive particles while he was studying at McGill, conducted the gold foil experiment and discovered the nucleus

What did the gold foil experiment prove?

Rutherford expected all the particles to go straight through, however, some deflected back which proved the existence of the nucleus

Who was Marie Curie?

Polish born French scientist who discovered radium and polonium

What awards did Curie win?

She received the Nobel prize twice, first in 1903 of her investigation of radioactivity, and then in 1911 for her discovery of the elements radium and polonium

Who were Irene and Frederick Joliot-Curie?

French scientist who conducted an experiment in which they bombarded beryllium with alpha particles

Who was James Chadwick?

British scientist who discovered the nucleus by looking at the data from the Joliot-Curie's experiment with wax

Who was Niels Bohr?

Danish scientist who concluded that electron exist in energy levels

What did Niels Bohr believe about electrons?

• Electrons are in quantized energy levels

• Electrons can only absorb or emit energy as they move levels

What was Niels Bohr's model?

The planetary model; electrons orbit the positive nucleus in rings (principal energy levels)

What did the Ancient Greeks believe about matter?

They believed matter was composed of four basic elements: earth, water, fire, and air

Proton (charge, relative mass, actual mass, location)

1+, 1 amu, 1.673x10^-24g, nucleus

Neutron (charge, relative mass, actual mass, location)

0, 1, 1.675x10^-24g, nucleus

Electron (charge, relative mass, actual mass, location)

1-, 0, 9.109x10^-28g, outside nucleus

Mass number

Number of protons and neutrons (top left)

Atomic number

Number of protons (bottom left)

Isotopes

Atoms of the same element with different numbers of neutrons (different mass number, same atomic number)

What is the approximate size of the largest atom?

10^-8 cm in diameter