Does lightning have mass? My chemistry teacher/book states that lightning is just light, and therefore has no mass and takes up no space (we're not very far through the book yet, it's defining matter).
However, I take issue with this statement - it feels wrong. My reasoning is this: Lightning, as far as I know, is simply electrical energy. Also, I believe that electrical energy needs a medium to travel through, right? 
If this is true, wouldn't the air the lightning travels through be the mass and space the lightning takes up?
 A: It depends on how you define "lightning". When electrons flow from clouds to the earth, ionizing the air and producing light, does your definition include the electrons, the air, the plasma, the light, or a subset?
Pedantically speaking, I would say that lightning is the flow of electrons, and to me a flow is an abstract idea (the action of moving in a steady, continuous stream) instead of a concrete object with a mass.
A: Lightning must have some mass, how else is thunder created. If thunder is the sonic boom created by lightning moving faster than the speed of sound, then lightning must have mass. I don't hear thunder every time I turn a flashlight on. 
A: Lightning is not 'just light', it is according to this NOAA National Severe Storms Laboratory FAQ,

Lightning, as best we understand, is a channel of electrical charge, called a stepped leader that zigzags downward

So, technically speaking, the mass of a lightning bolt could be the sum of all the electrons and the plasma within the electrical charge channel. (thank you to tpg2114)
Each electron has a mass of about $9.11 × 10^{-31}$ kilograms, but it would not really be feasible to exactly count how many electrons there are in a single lightning bolt, hence, not feasible to get an exact mass.
