CH 1.2 Atomic Structure: The Development of Atomic Theory

Vocabulary-style flashcards defining the major figures, theories, and concepts in the history and development of atomic structure.

Democritus

Coined the term atom (meaning indivisible particle), and stated that atoms come in different sizes, are in constant motion, and are separated by empty space.

Alchemists (1-1800)

Group that studied the nature of matter, searched for the Elixir of Life, believed metal could be transformed into gold, and created lab glassware, equipment, alloys, and chemical handling procedures.

John Dalton's Atomic Theory

Theory stating that: i) all matter is made up of atoms, ii) all atoms of an element are identical, iii) atoms of different elements are different, and iv) atoms are rearranged in chemical reactions, but never created or destroyed.

James Maxwell (1865)

Proposed the classical theory that light is an electromagnetic wave with electric and magnetic fields that exert forces, introducing the electromagnetic spectrum.

Heinrich Hertz (1887)

Discovered the photoelectric effect and demonstrated that the frequency (colour) of light, rather than its intensity, is most important in determining the kinetic energy of displaced electrons.

J.J Thomson

Discovered the electron as a negatively charged, extremely small part of the atom, which was thought to be evenly spaced in a positively charged sphere.

Max Planck

Observed heated solids glowing red to white and suggested that matter can only gain or lose energy in whole number multiples of a small quantity called a quantum.

Quantum

A small quantity of energy representing the discrete units in which oscillating atoms in a heated solid absorb or emit energy.

Photon

A quantum of light energy absorbed by electrons to break free and gain kinetic energy during the photoelectric effect.

Ernest Rutherford

Proposed that the nucleus is made up of positively charged protons surrounded mostly by empty space occupied by electrons, and predicted a neutral particle of equal mass to the proton.

Erwin Schrödinger (1926)

Proposed that electrons act as both a wave and a particle, using wave mechanics and probability to model distinct energy levels and regions around the nucleus called orbitals.

Orbital

A region in space around the nucleus where an electron is most likely located, based on probability and wave mechanics.

Heisenberg's Uncertainty Principle (1927)

States that it is impossible to simultaneously know both the position and speed of an electron.

James Chadwick

Confirmed that the nucleus contains neutral particles called neutrons, which have no charge.

Niels Bohr

Proposed that electrons orbit the nucleus in definite energy levels, can jump between energy levels, and that each energy level holds a specific number of electrons.

Number of Neutrons Formula

Calculated using the relationship $\text{Number of neutrons} = \text{mass number} - \text{atomic number}$.