Periods in the periodic table (Horizontal): Determines the number of electron shells.

Groups in the periodic table (Vertical): Group Number = number of electrons in their valence shell.
AKA they have the same chemistry
The MAGNITUDE of the reactions increase as you go DOWN in periods like K is worse than Li

Main group elements:
Easiest to understand.

Transition Metals:
They have different charges, which means they can have multiple different charges.

Lanthanoids and actinoids: The elements that aren’t inside the periodic table, and are all radioactive and weird.

Nobel gases: Basically perfect, so they don’t have to react with other atoms,

Alkali Metals: SUPER reactive to water.

Conducts electricity, is malleable, and shiny

Doesn’t conduct electricity and isn’t malleable

Metalloids / Semimetals:
They always LOOK like metals, but they have some characterizes from both groups.

There is a little staircase between metals and nonmetals starting between Boron and Aluminum and then going down one and then right one, etc.
The elements on the left are metals, the elements on the right are non-metals, and the elements around it are metalloids.