Just because an atom satisfies its octet doesn’t mean that it is stable. We also have to consider valance electrons. Sounds familiar? Let’s look into what those are.
Every dot = 1 valance electron, and every stick = 1 valance electrons. (Octet is different, see above.)
All of these carbons satisfy their octet, but only one of them is actually stable. The others suck. How can we tell which one will be stable?
Example: Understanding the hydrogen isotopes.9m
We can predict how many valance electrons each atom wants to have by looking up it’s Group Number on the periodic table.
In our example above, carbon is in Group 4A, meaning that it wants to possess 4 valance electrons, making the first structure the most stable.
Now you have to guess what an atom looks like in it’s neutral state! Simply use the periodic table to look up this information.