Molecules,+Diatomic+Molecules

=Molecules=

//Two or more atoms tightly bound together by covalent bonds that behaves as a single entity. Molecules are generally made up of only nonmetals.//

There are many molecules that we encounter on an everyday basis. Some molecules consist of atoms of only one type of element, while other molecular compounds consist of atoms of two or more elements. Every molecule has a chemical formula, which indicates the number and kind of elements contained in it.

Example
There are two common forms of oxygen: 1)"normal" oxygen found in the air we breathe has two oxygen atoms, and is thus denoted O2. 2)O3, or ozone The chemical formula is vital here because, although both are composed of only oxygen, they have drastically different characteristics. O3 is toxic while O2 is life-giving.

Space-filling model of ozone. Model of diatomic Oxygen. http://en.wikipedia.org/wiki/Image:Ozone-3D-vdW.png http://www.globalwarmingart.com/images/a/a4/Oxygen_Molecule_VdW.png

The difference between water and hydrogen peroxide are similar. H2O, again, a compound vital to life, contains the same elements as H2O2, yet concentrated hydrogen peroxide is used in industry as a bleaching agent for the production of paper, and is corrosive to metal. Of course, its most common domestic use is in low concentrations to clean wounds, yet it is still clear that it is not something you would want to drink. Ball-and-stick model of a water molecule http://www.btinternet.com/~martin.chaplin/images/molecul1.gif

Ball-and-stick model of hydrogen peroxide http://en.wikipedia.org/wiki/Image:Water_molecule_3D.svg

Some other common molecules are carbon monoxide, carbon dioxide,  acetate, and methane.


 * Diatomic Molecules** are composed of only two atoms of the same element. There are seven such molecules: hydrogen, nitrogen, oxygen, and the halogens fluorine, chlorine, bromine, and iodine. The chemical formulas for these are, H2, N2, O2, etc.

There are several mneumonic devices that can be utilized to remember these:

=HONClBrIF=

=ClIF BrOHN= =The Magic 7=

The halogens, oxygen, and nitrogen form a number "7" that points to the seventh diatomic molecule, hydrogen. http://www.doccasagrande.net/Images/Periodic_Table.jpg

References

Brown, LeMay, Bursten. __Chemistry: The Central Science.__ Prentice Hall, 2003.

Wikipedia: The Free Encyclopedia.