The Periodic Table

Atoms, Molecules and Ions

The Periodic Table

The Periodic Table

As more and more elements were discovered and characterized, efforts were made to see whether they could be grouped, or classified, according to their chemical behavior. This effort resulted, in 1869, in the development of the Periodic Table.

Certain elements show similar characteristics:

Lithium (Li), Sodium (Na) and Potassium (K) are all soft, very reactive metals
Helium (He), Neon (Ne) and Argon (Ar) are very non-reactive gasses

If the elements are arranged in order of increasing atomic number, their chemical and physical properties are found to show a repeating, or periodic pattern.

Note: This table lists the atomic number (number of protons) in the upper left corner of each box. The atomic number is formally placed as a subscript preceding the atom name.

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As an example of the periodic nature of the atoms (when arranged by atomic number), each of the soft reactive metals comes immediately after one of the nonreactive gasses.

The elements in a column of the periodic table are known as a family or group. The labeling of the families are somewhat arbitrary, but are usually divided into the general groups of:

Metals (everything on the left and middle region)
Non-metals (upper diagonal on the right hand side - green, salmon and red)
Metaloids (atoms in the boundary between the metals and metaloids: Boron(B), Silicon(Si), Germainium(Ge), Arsenic(As), Antimony(Sb), Tellurium(Te), Astatine(At)). These are some of the more useful materials for semi-conductors.

or, another convention is the 'A' and 'B' designators with column number labels (either in Roman or Arabic numerals). These columns have different types of classifications:

Group	Name	Elements
1A	Alkali metals	Li, Na, K, Rb, Cs, Fr
2A	Alkaline earth metals	Be, Mg, Ca, Sr, Ba, Ra
6A	Chalcogens ("chalk formers")	O, S, Se, Te, Po
7A	Halogens ("salt formers")	F, Cl, Br, I, At
8A	Noble gases (or inert, or rare gases)	He, Ne, Ar, Kr, Xe, Rn

The elements in a family of the periodic table have similar properties because they have the same type of arrangement of electrons at the periphery of their atoms.

The majority of elements are metals:

high luster
high electrical conductivity
high heat conductivity
solid at room temperature (except Mercury [Hg])

Note: hydrogen is a non-metal (at left hand side of the periodic table)

Non-metals

solid, liquid or gas at room temp

1996 Michael Blaber