Elements & Atoms

• Atomic theory grew as a series of models that developed from experimental evidence. As more evidence was collected, the theory and models were revised.

Elements & Atoms

• Dalton Model – atoms are like smooth, hard balls that could not be broken into smaller pieces. (See p. 8 – Summary of Dalton’s Ideas)

Solid Sphere Model orBilliard Ball Modelproposed by John Dalton

Elements & Atoms

• Thomson Model – atoms have negatively charged electrons embedded in a positive charge.

Plum Pudding Model orRaisin Bun Modelproposed by J.J. Thomson

Elements & Atoms

• Rutherford’s Gold Foil Experiment – most particles pass through foil in straight line, but a few were strongly deflected. This led to proposal of Rutherford Model, small, positively charged nucleus in center of the atom.

Rutherford Model of a lithium atom.

Elements & Atoms

• Bohr’s Model – electrons move in specific orbits around the nucleus of an atom.

The Bohr atom

Elements & Atoms

• Cloud Model – electrons move rapidly in every direction around the nucleus.

Elements & Atoms

• Modern Atomic Model – nucleus, which contains both protons and neutrons, is surrounded by a cloudlike region of electrons.