Quantum Mechanical Model of Atoms

Atomic Theory

• a scientific concept

• explains the nature of matter and its behaviour

Atomism

• first theory proposed by Democritus

• made in the 5th century B.C.

• all matter is made up of tiny, invisible particles called atoms

Solid Sphere Model

• by John Dalton

• made in 1803

• it was made as an attempt to describe the structure of the atom

• in this model, atoms are tiny, indestructible sphere with no internal structure

Plum Pudding Model

• by J.J. Thompson

• made in 1904

• atom: composed of a positively charged sphere with negatively charged electrons distributed throughout it

• “pudding” because the negatively charged electrons were embedded into the postive charge like a pudding, it made up most of the atom’s mass

Nuclear Model

• by Ernest Ruthford

• made in 1911

• mass of an atom: concentrated in a tiny, positively charged nucleus at the center, negatively charged electrons orbited around it

• became the basis for understandiing the atomic structure today

Bohr’s Atomic Model

• by Neil Bohr

• made in 1922

• nucleus is surrounded by outer shells that held electrons

• farther shells from the nucleaus → more electrons it can hold

Electron Cloud Theory

• by Erwin Schrodinger

• made in 1926

• behaves as waves

• electrons → found in a cloud of probability, no exact position, likely to be found in the electron orbitals