Atomic Structure

Atomic Structure is the thirteenth lecture within the Properties of Matter subtopic of PH1011. It covers initial concepts of the atom, Rutherford Scattering, nuclear density and various calculations.

Previous: X-Rays

Next: Radioactivity I

Rutherford Scattering
Thompson discovered the electron in the 19th century, and concluded that the atom was likely to exist in a "plum pudding" model; a sea of electrons around apositive point charge. This was disproven when Rutherford fired alpha particles at gold foil - many were deflected instead of passing directly through. This allowed the current understanding of the atom to be mae - a very small nucleus surrounded mostly by empty space.

Neutrons
Neutrons only exist stably in the nucleus itself - they will otherwise decay into a proton, neutron and anti-electron neutrino, with a half life of 10.3 minutes. Neutrons are approximately equal mass to protons (where electrons are 1/1840 amu) and carry no charge.

Atoms
The density of the nucleus can be found by considering H - the radius is ~10-10m, with volume roughly equal to r3 - if the mass of the atom is equal to that of a proton then mass = 1.7x10-27. This gives density = m/V = 1.7x103. The density of an atom is concentrated almost entirely in the atomic nucleus - at ~ 1018kg/m3, it is perhaps the most dense matirial in existence. A similar density is found in neutron stars.

Atomic notation is given the form AZE; Z being the atomic number and A being the mass number.

Isotopes are atoms with a differing number of neutrons to their usual counterparts. Their relative abundance can be calculated if the atomic mass and relative atomic mass is known - Average atomic mass = %1M1 + %2M2 + ... + %nMn.

Summary
The atom consists of a dense nucleus amongst quantised electron orbitals.