Well, first off, when you arrange a series of atoms properly, you get an object. A brain. Scissors. That's not so tough. You need iron atoms to get scissors, but you don't have scissors if you just have iron.
Consciousness is also a process. The brain needs to be 'on' to have consciousness. Materialists think you can turn a brain off, and then turn it back on (excepting damage) and still have a brain.
Can something other than a human brain be conscious? Sure. Just like something other than scissors can cut paper. Basically, consciousness is the action that a brain will perform (when used properly) just like cutting is what scissors will do when used properly.