Chapter 3

Atomic Structure

The atom is the basic building block of matter, representing the smallest unit of a chemical
element. An atom in turn is composed of subatomic particles called protons, neutrons, and
electrons. In 1911, Ernest Rutherford provided experimental evidence that an atom has a dense,
positively charged nucleus that accounts for only a small portion of the volume of the atom but
nearly all the mass. The protons and neutrons in an atom form the nucleus, the core of the atom.
The electrons exist outside the nucleus in characteristic regions of space called orbitals. All atoms of
an element show similar chemical properties and cannot be further broken down by chemical
means.

Subatomic   Particles

Atomic  Weights and Isotopes

Bohr’s  Model   of  the Hydrogen    Atom

Quantum Mechanical  Model   of  Atoms

Electron    Configuration   and Orbital Filling