When consuming alcohol, what is happening at atomic or molecular level in the brain?

Depressant: Alcohol increases effects of an inhibitory neurotransmitter GABA which sedates, causes the sluggishness. Also, it inhibits the excitatory neurotransmitter glutamate, also depresses brain. Result is a physiological slowdown. It is also thought to impact Dopamine which causes the pleasant feelings, which might stimulate more drinking. More than this, but this is the brief response.