

The periodic table of the elements is the basic roadmap used by chemists. An element is a substance that consists of a single kind of atom. Approximately 92 different elements occur in nature. Each element has different chemical properties, although some are very hard to distinguish.

Elements can be numbered (their atomic number) starting at 1 for hydrogen and going up, based on the element's number of protons. Russian chemist Dmitri Mendeleev in 1869 published a sequential table of the elements laid out in rows and columns. Elements in the same column had similar chemical behavior; their properties were periodic. Furthermore, this was more than just a graphical trick. Mendeleev predicted that new elements would be found where his table had gaps, and he estimated their properties based on the known elements around it. The discoveries of scandium, gallium, and germanium proved out his predictions.

The modern periodic table (below) has been expanded. The lanthanide row and the actinide row are usually placed below the main table. But, this periodic table is still recognizably the same concept and useful. Each element has a name, an atomic number, and a one- or two-letter chemical symbol.

Many of these elements are discussed as limited resources in the sections on resource metals, precious metals, and minerals. Click on the chemical symbol for the link.
are reactive metals on the left side of the table.
Alkaline earth metals are slightly less reactive metals in the second column.
Rare earth metals are a group of elements with very similar chemical properties. Fifteen of them, starting with 57 lanthanum are usually placed together underneath 39 yttrium.
Actinides are heavy radioactive metals. Elements above 92 uranium are synthetic and are not found in nature(excepting traces of 93 neptunium and 94 plutonium).
include what are called the transition metals, the precious metals, and some low-melting-point metals toward the right of the table.
have some characteristics of metals but not all.
are various solids and gases that do not fit the other categories.
Halogens are nonmetallic elements that are very reactive with elements to their left in the table.
Noble gases are inert gases that are always found as pure elements and do not make chemical combinations.
Dark grey elements with high atomic numbers are discovered so recently that their chemical properties are still unknown.

Alkali metals | Alkaline earth metals | Rare earth metals | Other metals | Metalloids | Nonmetals | Halogens | Noble gases | ||||||||||
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Meitnerium
109
Mt
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Darmstadtium
110
Ds
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Roentgenium
111
Rg
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Ununtrium
113
Uut
|
Flerovium
114
Fl
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Ununpentium
115
Uup
|
Livermorium
116
Lv
|
Ununseptium
117
Uus
|
Ununoctium
118
Uuo
|
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** |
Curium
96
Cm
|
Berkelium
97
Bk
|
Californium
98
Cf
|
Einsteinium
99
Es
|
Fermium
100
Fm
|
Mendelevium
101
Md
|
Nobelium
102
No
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Lawrencium
103
Lr
|