Atomic Theory

Democritus

discovered atoms at 400 B.C. and called it “atomos” (Greek word) which defines as uncuttable, indivisible, and unbreakable.

John Dalton

british chemist and physicist who proposed the Solid Sphere Model in the early 19th century.

Solid Sphere Model

according to this theory, atoms are tiny balls that can’t be broken and are all made of the same material. Explained how chemicals mix together and what makes them different.

J.J. Thomson

english physicist known for his work on the nature of electrons. Proposed the Plum Pudding model in the late 19th century.

Plum Pudding Model

atoms are like plum pudding with tiny positive charges scattered throughout a cloud of negative electrons. Explained why atoms have a neutral charge.

Ernest Rutherford

new-zealand born physicist known for his contributions to nuclear physics. Introduced the nuclear model in the early 20th century.

Nuclear Model

atoms have a nucleus with a positive charge and most of the mass, surrounded by electrons that orbit like planets. Explains why particles can pass/bounce through atoms. The basis of our current understanding of atomic structure.

Neils Bohr

danish physicist known for his pioneering work in the atomic structure. Proposed the Planetary Model in the early 20th century.

Planetary Model

electrons orbit the nucleus of an atom in a specific energy level/shell. Explained why atoms emit light and absorb colors of light. Also explained the stability of atoms.

Erwin Schrodinger

Austrian physicist renowned for his contributions to quantum mechanics. Proposed the Quantum Model in the 1920s.

Quantum Model

electrons exist as a probable wave-like pattern around the nucleus, not in a specific orbit. Explains why electrons act like particles and waves.

Nucleus

center of the atom. It is where all of the mass of the atom is contained.

Protons

positively charged subatomic particles. Found in the nucleus and have a relative weight of 1.

Neutrons

subatomic particles that have no charge. Found in the nucleus and have a relative weight of 1.

Electrons

negatively charged subatomic particles. Located in shells/energy levels around the nucleus. Have a relative weight of 0.

Atomic Number

the number of protons/electrons.

Relative Atomic Mass

the total mass of the nucleus. The mean relative mass of the atoms of the different isotopes in an element. It is the number of times heavier an atom is.