Atoms, elements and compounds
Atomic structure and the Periodic Table
| Particle | Relative charge | Mass (atomic mass units) |
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1840 |
Proton number: the number of protons in an atom (and the number of
electrons in an uncharged atom).
Nucleon number: the number of protons + neutrons in an atom.
In the periodic table, when you go one element to the right, you increase the proton number by 1. When you go one element down, you increase the proton number by 8 in the first 3 periods (where the transition elements are not included).
Isotope: atoms of the same element that have different numbers of neutrons e.g. Carbon 12 and Carbon 14.
There are non-radioactive isotopes and radio(active)-isotopes. Radio isotopes are unstable atoms, which break down giving radiation.
Medical use: cancer treatment (radiotherapy) – rays kill cancer cells using cobalt-60.
Industrial use: to check for leaks – radioisotopes called tracers are added to oil or gas. At the leaks radiation is detected using a Geiger counter, (if you need to name an element then say carbon 14 – used for carbon dating, when something dies it does not take in new carbon atoms, but it still has remaining carbon-14 atoms, the radiation can be measured to estimate how long ago something died).
Electrons are arranged in electron shells. Atoms want to have full outer shells (full set of valency electrons), this is why they react. Noble gases have full outer shells so they have no need to react. Electron shell structure: 2, 8, 8, 18. More reactive elements have a greater desire to have a full outer shell, so also form more stable compounds.