Development of Modern Atomic Theory

Question 1

Democritus (400 B.C.)

Answer 1

DISCOVERED ATOMS

- matter consisted of indivisible particles called atoms

Question 2

Dalton (1803)

Answer 2

“ATOMIC THEORY”

- perceived atoms to be solid little spheres

Question 3

Arrhenius (1832)

Answer 3

Discovered the electrical nature of chemical solutions

Question 4

Faraday (1834)

Answer 4

MATTER HAD ELECTRICAL PROPERTIES

experimented with electricity running through solutions

Question 5

KIRCHOFF (1859)

Answer 5

contributed to the understanding of:

• electrical circuits
• spectroscopy
• emission/absorption line spectra
• emission of blackbody radiation by heated objects

Question 6

Mendeleev (1869-1872)

Answer 6

determines that there’s a periodicity of physical and chemical properties of elements in the periodic table

Question 7

Crookes (1879)

Answer 7

CATHODE RAYS
- Rays with a NEG charge flowed from the CATHODE to the ANODE
(vacuum/Crookes tube)

Question 8

Goldstein (1886)

Answer 8

CANAL RAYS

- Rays with a POS charge flowed from the ANODE to the CATHODE

Question 9

Roëntgen (1895)

Answer 9

Discovered X-rays, and that they had NO charge

Question 10

Bequerel (1896)

Answer 10

DISCOVERED RADIOACTIVITY

uranium salt

Question 11

Thomson (1897)

Answer 11

DISCOVERED ELECTRONS
- determined the e/m ratio (charge/mass) of the electron
(plum pudding)
- quantitive studies of cathode rays

Question 12

PLANCK (1901)

Answer 12

Radiant energy is EMITTED?ABSORBED in discrete units called QUANTA

Question 13

Einstein (1905)

Answer 13

• Light/free radiant energy dissociated from all matter was PARTICULATE
• A PHOTON IS A QUANTUM OF LIGHT ENERGY
• light is made up of particles, each carried a definite amount of energy (QUANTUM)

Question 14

Millican (1909)

Answer 14

DETERMINED THE CHARGE OF THE ELECTRON
(oil drop experiment)

mass of electron = 0.00055u

Question 15

Rutherford (1911)

Answer 15

DISCOVERED THE NUCLEUS(
(gold foil experiment)

• “Nuclear Model”
• lowest charge on an ionized gas particle if from the hydrogen ion

Question 16

Soddy (1913)

Answer 16

Radioactive decay suggest different atoms of the same element

Question 17

Bohr (1913)

Answer 17

“PLANETARY MODEL” for atomic structure

using Rutherfords concept of a nuclear atom and Planck’s Quantum Theory

Question 18

Mosley (1914)

Answer 18

DETERMINED THE CHARGES ON NUCLEI of most atoms

• atomic number/number of protons was unique to each element

Question 19

Aston (1919)

Answer 19

THERE’S DIFFERENT MASSES FOR SOME ATOMS OF THE SAME ELEMENT

work with mass spectrometer

Question 20

de Broglie

Answer 20

MATTER (like light or any radiant energy) has both PARTICLE and WAVE like characteristics
(wave-particle duality)

Question 21

Schrödinger (1923)

Answer 21

Atom = positively charged nucleus that’s surrounded by vibrating electrical waves

• Electrons are described by four quantum numbers ( n, l, m(l), m(s) )
• described the location of electrons in an atom
  (using mathematical probability)

Question 22

Chadwick (1932)

Answer 22

DISCOVERED THE NEUTRON

bombardment of Beryllium