All substances are composed
of only about a hundred fundamental kinds of matter called
elements. Each element is made up of very small entities
called atoms ; all atoms of the same element behave identically
chemically.
Each element is designated by an atomic number, a name,
and a chemical symbol such as carbon, C, zinc, Zn.
Each element has a characteristic atomic mass which is
the average mass of all atoms of the element. The atomic
number is a unique, important way of designating each
element, and it is equal to the number of protons in the
nuclei of each atom of the element.
Metals,
nonmetals and metalloids :
Metals are elements that are generally solid, shiny in
appearance, electrically conducting, and malleable. They
tend to have only 1-3 outer electrons which they may lose
in forming chemical compounds. Examples of metals are
iron, copper, silver.
Nonmetals
often have a dull appearance, are not at all malleable,
and frequently occur as gases or liquid. Colorless oxygen
gas, green chlorine gas and brown bromine liquid are common
non metals. Nonmetals tend to have close to a full octet
of outer-shell electrons, and in forming chemical compounds,
they gain or share electrons.
Metalloids,
such as silicon or arsenic, are elements with properties
intermediate between those of metals and nonmetals –
under some conditions a metalloid may exhibit properties
of metals, and under other conditions, properties of non
metals.
Conventionally, trace elements are elements which are
present in low quantities in the earth, plants, animals
and man.
Mendeleïev’s periodic table (click on the table)
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Trace
Elements 
