How is the periodic table arranged?

The periodic table organizes the known elements of the world by increasing atomic

number (number of protons).

The periodic table also separates elements into categories- metals, nonmetal, or metalloids.

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There are five major groups of the periodic table:

• The alkai metals (group 1 but not hydrogen)- most reactive group of metals
• The alkaline earth metals (group 2)
• The transition metals (groups 3-12)
• The halogens (group 17)- most reactive group of nonmetals
• The noble gases (group 18)- will not react because they have a full valence.

image source: Mrs. Chen STREAM Unit 2 packet

Groups (Columns):

Elements in the same group (column)have the same number of valence electrons. Helium is the

exception to the rule. It only has 2 electrons but, it is like the noble gases because it is full

and will not bond with other elements.

Row (Periods): Elements in the same row have the same number of orbitals.

Periodic Table Blocks:

Atomic # = # of protons (different for each element)

Atomic mass = # of protons + # of neutrons

***to calculate the number of neutrons, subtract the

atomic number from the atomic mass.