A chemical formula is a
concise way of expressing information about the atoms that constitute a particular
chemical compound. It identifies each type of element by its chemical symbol and
identifies the number of atoms of such element to be found in each discrete molecule
of that compound. The number of atoms (if greater than one) is indicated as a
a simple molecule consisting of one carbon
atom bonded to four atoms has the chemical formula:
glucose with six carbon atoms, twelve hydrogen atoms and six oxygen atoms
has the chemical formula:
chemical formula may also supply information about the types and spatial arrangement
of bonds in the chemical, though it does not necessarily specify the exact isomer
. For example ethane consists of two carbon atoms single-bonded to each other,
each having three hydrogen atoms bonded to it. Its chemical formula can be rendered
as CH3CH3. If there were a double bond between the carbon
atoms (and thus each carbon only had two hydrogens), the chemical formula may
be written: CH2CH2, and the fact that there is a double
bond between the carbons is assumed. However, a more explicit and correct method
is to write H2C:CH2 or H2C=CH2. The
two dots or lines indicate that a double bond connects the atoms on either side
triple bond may be expressed with three dots or lines, and if there may be ambiguity,
a single dot or line may be used to indicate a single bond.
with multiple functional groups that are the same may be expressed in the following
way: (CH3)3CH. However, this implies a different structure
from other molecules that can be formed using the same atoms( Isomers). The formula
(CH3)3CH implies a chain of three carbon atoms, with the
middle carbon atom bonded to another carbon:
the remaining bonds on the carbons all leading to hydrogen atoms. However, the
same number of atoms (10 hydrogens and 4 carbons, or C4H10)
may be used to make a straight chain: CH3CH2CH2CH3.
alkene 2-butene has two isomers which the chemical formula CH3CH=CHCH3
does not identify. The relative position of the two methyl groups must be indicated
by additional notation denoting whether the methyl groups are on the same side
of the double bond (cis or Z) or on the opposite size from each
other (trans or E).
polymers, parentheses are placed around the repeating unit. For example, a hydrocarbon molecule
that is described as: CH3(CH2)50CH3,
is a molecule with 50 repeating units. If the number of repeating units is unknown
or variable, the letter n may be used to indicate this: CH3(CH2)nCH3.
ions, the charge on a particular atom may be denoted with a right-hand superscript.
For example Na+, or Cu2+. The total charge on a molecule
may also be shown in this way. For example H3O+.
isotopes are more relevant to nuclear chemistry than to conventional chemistry,
different isotopes may also be indicated as a left-hand superscript in a chemical
formula. For example, the radioactive phosphate ion is 32PO4-.