Video Transcript
How many atoms are there in a
single unit of the compound Al2(SO4)3?
First, we need to identify the
elements in the compound. Elemental symbols are either formed
of a capital letter or a capital letter followed by a lowercase letter. There are three different elements
in this compound: Al, aluminum; S, sulfur; and O, oxygen. But we need to know how many atoms
there are in a single unit of the compound. We need to use the subscript
values, or lack thereof, to calculate this. The subscript two after Al
indicates that one unit of the compound contains two aluminum atoms.
Let’s now look at the contents of
the brackets. The subscript four after O tells us
that there are four oxygen atoms. The absence of a subscript after S
tells us that there is only one sulfur atom. But the entire bracket has the
subscript three. Therefore, there’s actually a total
of three sulfur atoms and 12 oxygen atoms. These numbers can actually be
calculated by multiplying the subscripts for each atom within the brackets with the
subscript on the outside of the brackets.
So there are two aluminum atoms,
three sulfur atoms, and 12 oxygen atoms in a single unit of the compound
Al2(SO4)3. This sums to 17. Therefore, there are 17 atoms in a
single unit of the compound Al2(SO4)3.
