Which number indicates the number of atoms of each element in molecule of substance?

# Fe_2O_3# (or iron(III) oxide) there are #2# iron atoms and #3# oxygen atoms. The subscript to the bottom and right gives the number of atoms of each element.

In a chemical formula, the symbols for each element in the compound are followed by subscripts that tell us how many of that element are in the compound.

For an example, let's look at the the formula for compound glucose:

#ul("C"_6"H"_12"O"_6#

The subscripts that follow each element's symbol indicate how many of that element are in the compound.

We can see that in one molecule of glucose, there are

• #6# atoms of carbon (#"C"#)

• #12# atoms of hydrogen (#"H"#)

• #6# atoms of oxygen (#"O"#)

Sometimes, a compound may have the same element in different places in its compound, like how some alcohols such as ethanol are represented:

#ul("C"_2"H"_5"OH"#

Notice how #"H"# is located in more than one place. This is due to the fact that some compounds' chemical formulas show a representation of individual groups within the molecule.

For ethanol (and all alcohols), there exists an #-"OH"# group (called a hydroxyl group) at the end of the molecule, so it is often show as first the main carbon chain (#"C"_2"H"_5#), and then the hydroxyl group (#"OH"#).

Nevertheless, ethanol can still be represented as

#"C"_2"H"_6"O"#

Both formulas show us that in one molecule of ethanol, there are

• #2# atoms of carbon

• #6# atoms of hydrogen

• #1# atom of oxygen