What are some ways the periodic table is arranged?
They are listed in order of atomic number, which corresponds to number of protons in the nucleus. Then, each column is arranged to have similar properties. Especially “valence” related properties such as the types of ion that the atom forms. Hydrogen doesn’t really fit anywhere, but after that, Helium heads a column of very unreactive gasses called the “noble gasses” or “inert gasses”, next is Lithium, which heads a column of soft reactive metals that react violently with water turning it alkaline: the Alkali Metals. And the same principles continue across the whole table. The rare earths, actinides and lanthanides have such similar properties that they are all but indistinguishable. That is why they are sometimes shown as trying to occupy a single square.
