Fundamentals of Chemistry
CHARACTERISTICS OF ATOMS
TABLE 2 (Cont.)
Table of Elements
Name and Symbol
Molecules are groups or clusters of atoms held together by means of chemical bonding. There
are two types of molecule; molecules of an element and molecules of a compound.
Molecules of an Element
In certain cases, two single atoms of an element can be attracted to one another by a
bond to form a molecule. Examples of this are hydrogen, oxygen, and bromine. The
molecular formulas for these are H , O , and Br . Most gaseous elements exist as
molecules of two atoms.
Molecules of a Compound
Two atoms of different elements held together by a bond form a compound. The
molecule is the primary particle of a chemical compound. Some examples of this type of
molecule include hydrogen chloride (HCl), water (H O), methane (CH ), and
ammonia (NH ).
The weight of a molecule, the molecular weight, is the total mass of the individual
atoms. Therefore, it is fairly simple to calculate the mass of any molecule if its formula
is known (that is, the elements and the number of each that make up the molecule). Note
that the terms mass and weight are used interchangeably in chemistry.