Atomic Theory

Road Trip through Atomic Theory (Yes! You should take notes on

this.)

Democritus 400 B.C.» Atom: the smallest particle into

which an element can be divided and still be the same substance

» Democritus: Greek philosopher/scientist who came up with the idea of the atom

» Atomos means “uncuttable”» Didn’t do any experiments

John Dalton 1700’s» Dalton: British scientist,

creator of the atomic theory

» His theory states:a) All substances are made of

atoms. b) Atoms of the same element

are exactly alike, atoms of different elements are different.

c) Atoms join with other atoms to make new substances.

Thomson 1897» Identified an error in Dalton’s Atomic theory» Discovered there are small particles (called sub-atomic particles)

within the atom. The atom was in fact divisible (can be broken into pieces) which wasn’t previously thought by Dalton.

» Designed Cathode-Ray Tube experiment to prove his new theory=identified electrons.

» “Plum-Pudding Model”-atom is a positively charged blob of material with electrons (negative charges) scattered throughout.

Rutherford 1909» Former student of

Thomson’s» Created the Gold Foil

experiment: Proposed that lightweight, negative electrons move in empty space and that in the center of the atom is a tiny, very dense positively charged region called the nucleus.

Niels Bohr 1913» Danish Scientist who

worked with Rutherford.» Proposed that electrons

moved in paths at certain distances around the nucleus, called orbitals. Higher orbitals have more energy. When electrons move down orbitals, light (photons) is emitted.

James Chadwick, 1891-1974

» Discovered neutrons, a sub-atomic particle with no electrical charge.

» Neutrons have the same mass as a proton.

» Studied radioactivity and how to split an atom by shooting protons or neutrons at it. This led to nuclear power and nuclear weapons.

Modern Theory: Electron Clouds

» Erwin Schrodinger (Austrian) and Werner Heisenberg (German)-explained the nature of electrons in the atom.

» Electrons don’t travel in distinct paths as Bohr predicted but rather are likely to be found in certain regions called electron clouds.

Werner Heisenberg (1901- 1976)

» Proposed the Uncertainty Principle: you cannot predict the location of an electron.

Erwin Schrodinger

» Said that by observing an atom, you are affecting what the atom is. It could be in 2 states at once based on the sub-atomic particles.

» Proposed “Schrodinger’s Cat” theory.

Wave Theory

» Electrons have wave properties and are more complicated than Bohr’s electron orbitals.

» Electrons can behave as both particles and waves at the same time.

THE END! (Don’t Cry…)