Summary
Highlights
Nuclear physics studies the properties and reactions of an atom's nucleus. Early scientists proposed the Plum Pudding model, which imagined the atom as a positive pudding with electrons embedded. This model was later disproven.
Ernest Rutherford's experiment fired alpha particles at a thin gold foil. Most particles passed through, some deflected slightly, and a few bounced back. This led to the conclusion that a tiny, concentrated positive charge (the nucleus) exists at the heart of an atom, forming the Solar System model.
The atom consists of a nucleus (containing protons and neutrons, collectively called nucleons) in the center, with electrons orbiting it. A table summarizes the charges and masses of protons, neutrons, and electrons, highlighting that electrons are significantly lighter than protons and neutrons.
The number of protons determines the element. An element's notation includes its nuclear number (protons + neutrons) and proton number. Isotopes are elements with the same number of protons but different numbers of neutrons, leading to different masses but similar chemical properties.
Nuclear fission occurs when a uranium atom is hit by a neutron, making it unstable. This causes the uranium to split into two different elements, releasing additional neutrons and a large amount of energy. The total number of nucleons and protons/neutrons remains constant before and after the reaction.
Nuclear fusion is when two lighter nuclei, like hydrogen, combine to form a heavier nucleus, such as helium, along with a neutron and a significant release of energy. In both fission and fusion, a slight decrease in mass occurs, which is converted into a massive amount of energy according to Einstein's famous equation, E=mc².