Periodic Table

Horizontal rows = Periods
Vertical rows = Groups

*Number of electrons in the outer shell of the element determines the group it is in. [e.g. Na (sodium) has 11 electrons in the ratio 2:8:1. It has 1 electron in the outer shell so it is in Group 1.]

Group 1 metals are called alkali metals.
Group 2 metals are called alkali earth metals.
Group 7 elements are called halogens.

What are the definitions of atoms, molecules & ions?

What is an atom?
An atom is the basic unit of a chemical element.

What is a molecule?
A molecule is a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction.

-Monatomic - He, Ar
-Diatomic - O2, H2
-Triatomic - O3
-Polyatomic - S8


What is an ion?
An ion is an atom or molecule with a net electric charge due to the loss or gain of one or more electrons.