A History of the Atom: Theories and Models

Solid Sphere Model Date

1803

Plum Pudding Model Date

1904

Nuclear Model Date

1911

Planetary Model Date

1913

Model Date

1926

Niels Bohr's Theory

Bohr modified Rutherford's model of the atom by stating that electrons moved around the nucleus in orbits of fixed sized and energies. Electron energy in this model was quantified; electrons could not occupy values of energy between the fixed energy levels. + proposed stable electron orbits; explained the emission spectra of some elements - Moving electrons should emit energy and collapse into the nucleus model did not work well for heavier atoms

Solid Sphere Model

Dalton- an atom is little more than a singular, solid particle without other components.

Nuclear Model Creator

Ernest Rutherford

Nuclear Model

Ernest Rutherford - -Gold Foil Experiments -most of an atom's mass is in it's nucleus -the nucleus has a positive charge -electrons are in orbitals around the nucleus

Model Creator

Erwin Schrodinger

Quantum Model

Erwin Schrodinger - current atomic model in which a tiny, dense atomic nucleus is surrounded by a "cloud" of electrons occupying three-dimensional orbitals according to their energies

Erwin Schrodinger's Theory

Erwin Schrodinger stated that electrons do not move in set paths around the nucleus, but in waves. It is impossible to know the exact locations of the electrons; instead we have "clouds of probability" called orbitals, in which we are more likely to find an electron. + Shows electrons don't move around the nucleus in orbits, but in clouds where their position is uncertain + Still widely accepted as the most accurate model of the atom

John Dalton's Theory

His theory stated that all atoms are indivisible, those of a given element are identical, and compounds are different combinations of different types of atoms. + recognized atoms of a particular element differ from other elements - Atoms aren't indivisible (they're composed of subatomic particles)

Plum Pudding Model

J.J Thomson's - thought electrons were randomly distributed within a positively charged cloud

Plum Pudding Model Creator

JJ Thomson

Solid Sphere Model Creator

John Dalton

Planetary Model Creator

Niels Bohr

Planetary Model

Niels Bohr - electrons move around the nucleus in fixed, circular orbits

Ernest Rutherford's Theory

Rutherford fired positively charged alpha particles at a thin sheet of gold foil. Most passed through with little deflection, but some deflected at large angles. This was only possible if the atom was mostly empty space, with the positive charge concentrated in the nucleus. + Realized positive charge was localized in the nucleus of an atom - Did not explain why electrons remain in orbit around the nucleus

JJ Thomson's Theory

Thomson discovered electrons in atoms, subsequently producing the plum pudding model of the atom. It shows It shows the atom as composed of electrons scattered throughout a spherical cloud of positive charge.