Use model builder to place the test alkanes - the AtomPlacer3D is only for placing chains.
Throw an exception when a non-chain is provided. Documentation was also updated.
Test that providing a non-chain as a chain throws an exception.
Expect exception for a symbol we can't calculate the charge for - e.g. 'As' in this case.
Throw an exception if the symbol isn't supported.
JavaDoc error