looking for unique elements in chemical species
<p>Determining unique elements: Write a function which, when given a list of species,
will return an alphabetized list of the unique elements contained in the set of species.
Make use of the parser from the previous step. Example: calling your function with
an input of ['CO', 'H2O', 'CO2', 'CH4'] should return an output of ['C', 'H',
'O']</p>

<p>This is part of a larger project that I am doing. </p>

<p>The problem I am having is how to look at the individual characters of each element. Once I have this I should be able to check if its unique or not. I know this is not right, its just a rough idea of something I am thinking. </p>

<pre><code>def unique_elements(x):

    if x in y

    else
    y.append(x)
return y
</code></pre>
