The Nuclear Atom

Structure of an Atom

An atom contains a positively charged nucleus surrounded by orbiting negatively charged electrons.
An atom is electrically neutral
- Number of protons = Number of electrons
- Nucleus is Positively charged
The nucleus contains nucleons, which are positively charged protons and neutral neutrons.
- Number of Nucleons (A) = Number of Protons (Z) + Number of Neutrons (N)
- Nuclide Notation for Element (X): $_{Z}^{A}\textrm{X}$
An atom of an element that has a varying number of neutrons (same number of protons) in its nucleus is called an isotope of an element.
- A changes
- N changes
- Z remains the same

Rutherford’s Scattering Experiment

The size of an Atom is much larger than the nucleus (approximately 100,000 times).
This is proven by Rutherford’s experiment where a majority of $\alpha$ -particles ( $_{2}^{4}\textrm{He}^{2+}$ , Helium nucleus) go undeflected or deflect very little ( < $10^{\circ}$ ) upon passing through a thin gold foil.
A very small number are deflected by large angles, more than $90^{\circ}$ , which shows that only some of the positive $\alpha$ -particles interact with the positively charged Gold nucleus.
The Gold nuclei impacted show a negligible recoil, implying that they are massive, containing a majority of the mass of the atom.
These results imply that a majority of the atom is filled with empty space with a small nucleus and electrons orbiting it.

Nuclear Fission and Fusion

Nuclear Fission

$_{92}^{235}\textrm{U}+_{0}^{1}\textrm{n} \rightarrow \; _{36}^{94}\textrm{Kr}+_{56}^{139}\textrm{Ba}+3_{0}^{1}\textrm{n} + Energy$

A slow-moving neutron collides with the U-235 nucleus and triggers the fission reaction.
Note that there are 3 neutrons released by the reaction, which go on to cause a chain reaction by colliding with other U-235 nuclei.
Note that in the above nuclear equation, all the superscripts and subscripts add up to be the same on both sides.

Nuclear Fusion

It is a nuclear reaction in which low-mass nuclei combine at very-high temperature and pressure to form an intermediate-mass nucleus.
High temperatures are required to energize the nuclei enough to make them overcome electrical repulsion and fuse.

$_{1}^{3}\textrm{H}+_{1}^{2}\textrm{H} \rightarrow \; _{2}^{4}\textrm{He}+ _{0}^{1}\textrm{n} + Energy$

Note that in the above nuclear equation, all the superscripts and subscripts add up to be the same on both sides.