Chemistry Test- Atomic Theory

Early Atomic Theory

People believed that matter was made of the 4 elements: fire, water, earth and air. It was also believed that matter could be divided endlessly into smaller and smaller pieces. People relied on the power of their minds and intellectual thought as tools for scientific knowledge.

Democritus

First person to propose the idea that matter was not infinitely divisible. Believed that matter was made of tiny particles called atoms, atoms were solid and could not be created, destroyed, or further divided. Atoms moved through empty space.

Aristotle

Rejected the idea of atoms, did not believe that empty space could exist and made everyone reject Democritus’s ideas.

John Dalton

Proposed the modern atomic theory: Matter is made of atoms, atoms cannot be divided or broken down, atoms of an element are all identical, and atoms of different elements are different. Father of atomic theory.

J.J. Thomson

Discovered the electron through the Ray Tube experiment. The electron is a negatively charged sub-atomic particle. Also proposed the Plum pudding mode/chocolate chip model: a positively charged “jelly” which held the negative electrons.

Ernest Rutherford

Performed the gold foil experiment and discovered the existence of the nucleus. Determined that the atom consisted mostly of empty space, not positively charged “jelly”. Also concluded that most of the mass of the atom was contained in a tiny, dense positively charged region in the middle called the nucleus. Further defined the concept of the nucleus by the discovery of protons, concluded that the nucleus was made up of protons.

Niels Bohr

Discovered that the electrons have certain amounts of energy and travel in orbits around the nucleus, came up with the Bohr model.

Erwin Schrodinger

Developed the idea that electrons are found in a cloud and move in waves (electron cloud theory) The electron cloud theory is the current model we believe in today.

Werner Heisenberg

Developed an uncertainty principle to say that we cannot determine the speed and position of the electrons around the nucleus. Led to the development of quantum mechanics theory of the atom- that electrons are found in specific orbitals.

James Chadwick

Showed that the nucleus also contained a neutral sub-atomic particle, called a neutron