When a photon hits brick, it takes an electron from a low energy state to a higher energy state. It's like picking a ball up from the floor to the table. The ball can only be on the floor or the table. When the photon takes the electron from the 'floor' to the 'table', it is absorbed and so can not pass through.
When a photon hits glass, the excited state is way too high for the visible light photon to lift it up to that state. This means the light isn't absorbed and passes through. The gap between the 'normal' state and the excited state is called the energy gap.
http://www.sixtysymbols.com/videos/energygap.htm
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