Video Transcript
Which of the following is
equivalent to the chemical formula three CO2? (A) Three free carbon atoms and six
free oxygen atoms. (B) One molecule of triple carbon
dioxide. (C) Three carbon monoxide
molecules. (D) Three dioxycarbon
molecules. Or (E) three molecules of carbon
dioxide.
To answer this question, we first
need to understand the components of a chemical formula. A chemical formula is an expression
of chemical symbols and numerical subscripts that represent the composition of one
unit of a compound. So let’s take a closer look at the
chemical formula CO2. In this formula, we see a capital C
and a capital O. These are the chemical symbols of
carbon and oxygen.
Following the chemical symbol of
oxygen, we see a subscript two. A subscript after a chemical symbol
tells us the number of atoms of that element in one unit of a compound. No subscript appears after the
chemical symbol of carbon. This means that one unit of this
compound only contains one atom of carbon.
We now know that one unit of this
compound contains one atom of carbon and two atoms of oxygen. But what type of compound is CO2
and what is its chemical name? Both carbon and oxygen are
nonmetals. When atoms of two nonmetals form a
compound, the type of compound is a binary molecular compound, which consists of
atoms of two different elements, which are covalently bonded together.
So we now know that the carbon and
oxygen atoms are covalently bonded together to form one molecule. We can name this binary molecular
compound by writing the name of the first element in the chemical formula. The first element in the formula is
carbon. Next, we write the root of the
second element’s name, followed by the suffix I-D-E. The root of the word “oxygen” is
“ox,” to which we’ll add the suffix I-D-E. Finally, we’ll add Greek prefixes
in front of each word to indicate the number of atoms of each element in the
compound. But if there is only one of the
first element listed in the name, we won’t use the prefix mono-.
There is only one carbon atom, so
we won’t add a prefix to the word “carbon.” But there are two oxygen atoms, so
we need to add the prefix di- in front of the word “oxide.” So now we know that CO2 is a
molecule which contains one atom of carbon and two atoms of oxygen and has the name
carbon dioxide.
The last thing we need to account
for is the three written in front of CO2. Numbers written in front of a
chemical formula are called coefficients. Coefficients are used to indicate
the number of discrete units, either molecules or formula units, depending on the
type of compound. So placing a three in front of the
chemical formula CO2 indicates that there are three molecules of carbon dioxide. From this, we can determine that
the correct answer is answer choice (E). The chemical formula three CO2 is
equivalent to three molecules of carbon dioxide, answer choice (E).
