Chemists, Experiments, and Significance

Important Chemists

Published first modern chemistry textboook
- Contained list of substances that we now call elements
He and other chemists examined patterns in how elements combined to form compounds
Known as the "Father of Modern Chemistry"
Introduced the Law of Conservation of Mass
Helped develop a systematic chemical nomenclature
Conducted experiments that debunked the phlogiston theory

Explained law of definite proportions
Law of multiple proportions: the principle that, when two masses of one elements react with a given mass of another element to form 2 compounds, the two masses of the first element have a ratio of two small whole numbers

Cathode Ray experiment
- Helped to discover the electron
- In the experiment he discovered that cathode ray beams could be deflected by magnetic fields, revealing that cathode rays were not energy but charged particles of matter. The direction meant their charges were negative
- Developed the plum pudding model of the atom

Gold foil experiment proved the plum-pudding model was incorrect. because the beta particles that were shot through the goal foil were scattered widely, it showed that an atom has a large nucleus and not a positively charged cloud
Showed that there were several types of radioactivity
- Beta particles
  - negatively charged
  - Penetrate materials better
- Alpha particles
  - positively charged
  - 10,000 times bigger than beta particles

Determined the charge of an electron, and in so doing, its mass
Oil drop experiment
- In the experiment, x-rays ionized the air in a lower chamber that produced electrons that absorbed the tiny drops of water he had spritzed in. The descent of these drops could be altered by applying an electrical field with the plates above and below the chamber. Measuring the strength of the field and the rate of the fall of the drops, he could calculate the charge. By using Thomson’s mass:charge ratio, Millikan calculated the electron’s mas, which was super close to the actual charge of the electron that we use today.

Published papers on:
- The photoelectric effect: assumed that the energy of light is quantized
- HIs theory of special relativity
- Brownian motion
- The equivalence of matter and energy (E=mc²)

Avogadro’s Constant: the number of elementary particles in one mole of a substance (6.002 × 10²³)

Developed theory about electromagnetic properties
- According to this theory, electromagnetic radiation moves through space as waves with two perpendicular components: oscillating magnetic field and an oscillating electric field.
- Developed equations that describe almost all properties of light and other radiant energy.

Mapped the wavelengths of the absorption lines observed when sunlight passes through prisms

Explained atomic emission line spectra by proposing a new, quantized model of the H atom
Proposed model for hydrogen atom where electrons revolve around the nucleus in orbits

Explained blackbody radiation: assumed that energy absorbed/emitted by an object is quantized
Planck constant: a proportionality constant between energy and frequency.

Investigated the atomic emission spectra
Focused on the pattern of emission lines from hydrogen atoms
Formulated an equation which predicts the wavelengths of the emission lines in the visible spectrum of hydrogen.

Published a more general equation for predicting wavelength of hydrogens spectral lines

Assumed electrons could behave like waves as well as particles.
Used matter waves to explain the stability of the electron levels in Bohr’s model of the hydrogen atom

Proposed the thought: “What if we tried to watch an electron orbiting the nucleus of an atom.
We can’t really observe the momentum of the electron and its position at the same time so now we have the “Heisenberg uncertainty principle