1. Periodic Table Organization
Atoms are arranged according to the number of protons found in the nucleus.
They are listed in order because of periodic law, which states that elements tend to change in regular patterns when the are arrange in order of increasing atomic number.

2. The periodic table can be used to determine the electron configuration of an atom.
The horizontal rows on the periodic table are called periods.
Each row in the periodic table represents the number of energy levels that the atoms in the row contain.
For example Hydrogen (H) is in the first period and has one energy level.
Copper (Cu) is in the 4th period and has four energy levels.
How many energy levels does gold have?

3. The vertical columns are called groups.
Elements in the same group have similar properties, because they have the same number of valence electrons.
The columns are also arranged on the periodic table according to the electron orbitals of the different atoms.