Video Transcript
What is the chemical formula of
dichlorine heptoxide?
Recall the definition of a chemical
formula is an expression of chemical symbols and numerical subscripts that
represents the composition of one unit of a compound. An example of a chemical formula is
CH4, which is a compound with the chemical name carbon tetrahydride, or more
commonly known as methane. The chemical symbols C and H in the
chemical formula represent the element carbon and hydrogen, which can be found on
the periodic table in group 14, period two and group one, period one,
respectively. The numerical subscript four
indicates there are four hydrogen atoms in one unit, or one molecule, of the
compound.
Notice there isn’t a subscript next
to carbon’s chemical symbol. This is because a rule when writing
chemical formulas is that subscript values equal to one are implied but not written
in the chemical formula. So in the case of the carbon atom
in this chemical formula, there’s actually an implied number one, which means there
is one carbon atom in one unit of this compound.
To identify the chemical symbols
and numerical subscripts for the chemical formula of dichlorine heptoxide, we will
analyze the different parts of this chemical name. Firstly, the presence of two Greek
numerical prefixes di- and hept- indicates we are dealing with a binary molecular
compound, or a compound that is composed of atoms of two elements covalently bonded
together. With nonmetals and metalloids
consisting of the types of elements that covalently bond, for dichlorine heptoxide,
we will be looking for the elements and their chemical symbols on the right-hand
side of the periodic table, where all nonmetals and metalloids reside, with the
exception of the element hydrogen, which is the one nonmetal on the left side of the
periodic table.
Secondly, let’s break down the
chemical name into the following parts to determine the chemical formula: prefix,
root, and suffix. To determine the two elements
present, we look to the root words. As a rule for determining formulas
from names for binary molecular compounds, the first root word listed is the
element’s full name, as can be found on the periodic table. Therefore, the root word in
dichlorine is chlorine, which is an element on the periodic table with the chemical
symbol Cl found in group 17, period three.
The second root word is truncated
to only include the first portion of the element’s name and ends in the suffix
-ide. Therefore, in heptoxide, the root
word -ox- stands for the element oxygen, which has the chemical symbol O and is
found in groups 16, period two on the periodic table. The order elements are written in
their chemical name is the same order they’re written in their chemical formula. So we can start by writing the
chemical symbols Cl and O next to one another.
Now that we know the chemical
formula contains the elements chlorine and oxygen, we can use the Greek numerical
prefixes in front of each root word to determine the number of atoms of each element
in one unit of the compound. Referencing the Greek numerical
prefix list used in naming binary molecular compounds, the di- in front of
dichlorine indicates there are two chlorine atoms, with the number two written as a
subscript to the right of the chlorine atom in the chemical formula.
Notice the prefix in heptoxide is
written as hept- and not hepta- like it is shown in the table. This is because one of the naming
rule states that if the prefix in front of oxygen or oxide ends in the letter A or
O, the last letter of the prefix maybe dropped. So instead of writing the second
portion of the name as heptaoxide, since the prefix hepta- ends with an A and oxide
starts with an O, according to the rule, the last letter of the prefix, which is the
letter A, is removed and it is written and read as heptoxide.
In any case, the presence of the
prefix hept- indicates there are seven atoms of oxygen, which will also be written
as a subscript to the right of the oxygen chemical symbol in the chemical
formula. As a result, the chemical formula
for dichlorine heptoxide is Cl2O7.
