When you are joining atoms together, do not place a pink atom on the edge of the screen as you will be unable to complete your chain due to the unsatisfied requirements.
Always exchange a rabbit atom with one of the same colour within the chain you are building to make sure that you get rid of it as quickly as possible, because every rabbit atom on the screen speeds up the amount of atoms produced.
Build your chain in the middle of the game area and place all unwanted atoms on the outside edge to prevent cluttering. Try to make sure that all unwanted atoms are touching because you will be able to destroy them all if you get a radioactive atom and add it the line of unwanted atoms.
Be careful when placing heavy atoms because once you place them, you can't move them. Try to build them into the middle of a chain, or exhange them with atoms in a chain which you know you you will not be changing i.e. a heavy pink atom with a centrepiece pink atom. If you cannot do this, dump it on the edge and try to nuke it.
In the bonus levels, click quickly around the edge a lot of times to gain a selection of atoms to build a chain with. If you have a selection of atoms it will be easier to construct a chain within the time limit.