Development of Modern Atomic Theory

Question 1

Democritus

Answer 1

originated the notion
that matter consisted of indivisible particles called
atoms

Question 2

Dalton

Answer 2

revived the “atomic theory” of
atoms. He perceived atoms to be solid little
spheres.

Question 3

Arrhenius

Answer 3

discovered the electrical
nature of chemical solutions.

Question 4

Faraday

Answer 4

experimented with electricity
running through solutions. Discovered that matter
had electrical properties.

Question 4

Kirchhoff

Answer 4

contributed to the
fundamental understanding of electrical circuits,
spectroscopy (emission/absorption line spectra),
and the emission of blackbody radiation by heated
objects.

Question 4

Mendeleev

Answer 4

determines that there is
a periodicity of physical and chemical properties of
elements in the periodic table.

Question 4

Crookes

Answer 4

devised the “vacuum tube”
called Crookes tube. He discovered that rays with
a negative charge flowed from the cathode to the
anode in gas discharge tubes. These rays are
referred to as cathode rays. He did qualitative
studies of cathode rays.

Question 5

Röentgen

Answer 5

discovered X-rays and that
they had no charge

Question 5

Goldstein

Answer 5

discovered that rays with a
positive charge flowed from the anode to the
cathode in gas discharge tubes. These rays are
referred to as canal rays.

Question 6

Bequerel

Answer 6

discovered radioactivity
studying an uranium salt

Question 7

Einstein

Answer 7

proposed that light or free
radiant energy dissociated from all matter was
particulate. Light can be regarded as made up of
particles, each of which carries a definite amount
of energy (quantum). A photon is a quantum of
light energy.

Question 7

Thomson

Answer 7

discovered electrons. He
determined the e/m ratio (charge/mass) of the
electron. He proposed the Plum Pudding Model.
He did quantitative studies of cathode rays.

Question 8

Planck

Answer 8

proposed that radiant energy is
emitted/absorbed in discrete units called quanta.
E = h
(h = Planck’s constant = 6.626  10-34 J*s)
(v = frequency)

Question 9

Millikan

Answer 9

determined the charge of the
electron via the charged oil drop experiment. This
enabled the calculation of the mass of an electron
(0.00055 u).

Question 10

Rutherford

Answer 10

discovered the nucleus
conducting the “Gold Foil Experiment”. He
proposed the “Nuclear Model”. In 1914 he
discovered the lowest charge on an ionized gas
particle is from the hydrogen ion.

Question 11

Soddy

Answer 11

discovered that radioactive decay
suggests different atoms of the same element

Question 12

Bohr

Answer 12

using Rutherford’s concept of a
nuclear atom, and Planck’s Quantum Theory,
proposed the “Planetary Model” for atomic
structure

Question 13

Aston

Answer 13

his work with mass spectrometer
indicates that there are different masses for some
atoms of the same element.

Question 14

Moseley

Answer 14

determined the charges on the
nuclei of most atoms. He realized that the atomic
number/number of protons was unique to each
element.

Question 14

de Broglie

Answer 14

proposed that matter, like
light or any type of radiant energy has both
particle and wave like characteristics (waveparticle duality).

Question 15

Schröedinger

Answer 15

visualized an atom as a
positively charged nucleus surrounded by
vibrating electron waves. He used mathematical
probability to describe the location of electrons in
an atom. Electrons are described by four quantum
numbers: n, l, ml and ms

Question 16

Chadwick

Answer 16

discovered the neutron
through the bombardment of beryllium