A period 3 element is one of the chemical elements in the fourth row (or period) of the periodic table of the elements.

These are:

Chemical elements in the third period
Group 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
#
Name
11
Na
12
Mg
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
e--conf

Alkali metalsAlkaline earthsLanthanideActinidesTransition metals
Other metalsMetalloidsNonmetalsHalogensNoble gases

Period 1 element - Period 2 element - Period 3 element - Period 4 element - Period 5 element - Period 6 element - Period 7 element - Period 8 element -