Period 3 element

A period 3 element is one of the chemical elements in the third row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behavior fall into the same vertical columns. The third period contains eight elements: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine, and argon. The first two, sodium and magnesium, are members of the s-block of the periodic table, while the others are members of the p-block. Note that there is a 3d orbital, but it is not filled until Period 4, such giving the period table its characteristic shape of "two rows at a time". All of the period 3 elements occur in nature and have at least one stable isotope.

Periodic trends

Sodium

Magnesium

Aluminium

Silicon

Phosphorus

Sulfur

Chlorine

Argon

Atomic radius

Calculated period 3 atomic radii in picometers.

Main article: Atomic radius

As the atomic number of elements in Period 3 increases, the atomic radius decreases.

Electronegativity

Main article: Electronegativity

As the atomic number of elements in Period 3 increases, the electronegativity increases.

Ionization energy

Main article: Ionization energy

As the atomic number of elements in Period 3 increases, the ionization energy generally increases.

Elements

Chemical element			Chemical series	Electron configuration
11	Na	Sodium	Alkali metal	[Ne] 3s1
12	Mg	Magnesium	Alkaline earth metal	[Ne] 3s2
13	Al	Aluminium	Poor metal	[Ne] 3s2 3p1
14	Si	Silicon	Metalloid	[Ne] 3s2 3p2
15	P	Phosphorus	Nonmetal	[Ne] 3s2 3p3
16	S	Sulfur	Nonmetal	[Ne] 3s2 3p4
17	Cl	Chlorine	Halogen	[Ne] 3s2 3p5
18	Ar	Argon	Noble gas	[Ne] 3s2 3p6

Sodium

Main article: Sodium

Sodium (symbol Na) is an alkali metal. It is present in Earth's oceans in large quantities in the form of sodium chloride.

Magnesium

Main article: Magnesium

Magnesium (symbol Mg) is an alkaline earth metal. Magnesium ions are found in chlorophyll.

Aluminium

Main article: Aluminium

Aluminium (symbol Al) is a poor metal. It is the most abundant metal in the Earth's crust.

Silicon

Main article: Silicon

Silicon (symbol Si) is a metalloid. It is a semiconductor, making it the principal component in many integrated circuits.

Phosphorus

Main article: Phosphorus

Phosphorus (symbol P) is a nonmetal. It is highly reactive, and as such is never found in nature as a free element.

Sulfur

Main article: Sulfur

Sulfur (symbol S) is a nonmetal. It is found in two amino acids: cysteine and methionine.

Chlorine

Main article: Chlorine

Chlorine (symbol Cl) is a halogen. It is used as a disinfectant, especially in swimming pools.

Argon

Main article: Argon

Argon (symbol Ar) is a noble gas, making it almost entirely nonreactive. Incandescent lamps are often filled with noble gasses such as argon in order to preserve the filaments at high temperatures.

Table of elements

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.

Element categories in the periodic table

Metals						Metalloids	Nonmetals			Unknown chemical properties
Alkali metals	Alkaline earth metals	Inner transition metals		Transition metals	Post-transition metals		Other non-metals	Halogens	Noble gases
		Lanthanides	Actinides