These molecules are . Two ball-and-stick models of molecules. The first model has a chain of four black balls connected successively. Each of the two black balls, which are at the ends of the chain, has three white balls attached. Each of the two other balls has two white balls attached to them. The second model has a chain of three black balls connected successively. The central ball has one white ball and one black ball attached. This last-mentioned black ball has three white balls attached to it. Each of the two black balls, which are at the ends of the chain, has three white balls attached.