Everything in your brain part from the neuron impulses that are of electric nature, is chemistry. But when they say chemical imbalance, they do not at all talk about the chemical compounds that build up your brain cells (grey and white matter), when they say chemical, they are referring to transmitter substances ONLY.

I think this is part of why this "theory" is so pleasing to the masses, because they don't understand the basics of the brain so they think when they hear chemical, they think about everything that is of matter in the brain. It should be called the transmitter substance theory but then again that would confuse people.

Like I said, people need simplified explanations. Even when they are not true.