One of the seemingly tricky parts of chemistry is learning how to interpret chemical formulas
and count the atoms.
The first thing you must know is how to identify an element from the formula.
Element symbols on the periodic table
follow strict rules.
If there is only one letter in the symbol, it is capitalized.
If there are two letters in the symbol, the first letter is capitalized
and the second letter is lowercase.
This helps you identify the elements in a compound
like this one.
There aren't three atoms here just becase
there are three letters
there are only two: potassium and bromine.
In an even more complicated formula, you can still
find the elements by carefully looking out for those lowercase letters.
They go with the capital letter before them.
So we have sodium, hydrogen, carbon, and oxygen.
But, what about the little numbers? The subscripts?
Subscripts tell you how many of the atom are bonded in the compound.
The subscript only applies to the element written just before it.
So there are three oxygen atoms in this formula.
In this formula for glucose, there are
6 carbon atoms
And six oxygen atoms.
12 hydrogen atoms
There is even another trick up the chemists' sleeve:
A coefficient is a number in front of a chemical formula
that acts as a multiplier.
Everything after that coefficient is multiplied by the coefficient.
So instead of there being one sodium atom and one chlorine here,
there are actually two sodiums and two chlorine atoms,
because there are two of the whole sodium chloride compound.
The last trick involves chemical formulas with parenthesis.
When you see parenthesis around part of the chemical formula
that means there are multiples of that part.
The subscript outside the parenthesis tells you how many multiples there are.
In this case, there are 3 CO3s.
The number outside the parenthesis does not apply
to anything that's away from the parenthesis.
So the aluminum is not multiplied by 3, only the 2 subscript that's directly next to it.
So, to total all the atoms of elements here
there are two aluminum atoms
3 carbon atoms
because the 3 after the parenthesis is the multiplier
and 9 oxygen atoms because 3 times 3 is 9.
Now let's try a really fancy formula.
This is ammonium sulfate.
Let's look through each element and count the
atoms as we go.
Nitrogen is first, and the two outside the parenthesis is a multiplier
so we have 2 nitrogen atoms
hydrogen is next.
and there's a subscript 4 next to it, and the two multiplier outside the parenthesis, so
4 times 2 is 8.
The next element is sulfur
and it has no subscript and no parenthesis so
there's just 1 atom
And lastly, oxygen has a subscript of 4 so there are four atoms.
If you were looking at a chemical equation
and there was a coefficient in front of the formula
everything would be multiplied by that number
so the 2 in front of ammonium sulfate here, doubles the number of atoms we have, like this.
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