The rows in the periodic table present the elements in order of atomic number and the columns organize elements with similar characteristics, such as the same number of electrons in their valence shells. Columns are often labeled from left to right with Roman numerals I to VIII, and Arabic numerals 1 through 18. The elements in columns I and II have 1 and 2 electrons in their respective valence shells and the elements in columns VI and VII have 6 and 7 electrons in their respective valence shells.

The oxygen we breathe is formed when one oxygen atom covalently bonds with another oxygen atom to make the molecule O2. The subscript 2 in the chemical formula indicates the molecule contains two atoms of oxygen.

An element cannot be broken down chemically into a simpler form and retains unique chemical and physical properties. Each element behaves in a unique manner in nature.

A rock is a substance that contains one or more minerals or mineraloids.

the classic definition of a mineral is: Naturally occurring Inorganic Solid at room temperature Regular crystal structure Defined chemical composition