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So some of its properties depend on the electromagnetic radiation concerned (eg. visible light, radiation with a wavelength between 400..800 nm)

Size : cann not be determined. In fact it has been proved that it can not be determined (principle of Heisenbergh).

Mass : with each photon there is some energy related. If energy would be expressed in J (Joules), you have normally very small numbers eg 10^ -19. Substituting those numbers in the well known relation of Einstein

E = m c ^ 2

and solving for m : m = E / c ^2, you can calculate the mass. (in kg per photon)

Suppose a photon has an energy of 1 * 10 ^ -19 Joules (somewhere in the visible light). The corresponding mass is then :

1*10^ -19 * (3 * 10 ^5) ^ 2 =

9 * 10 ^ - 9 kg

At the moment a photon interacts with some matter, if the energy of the photon is not similar to the difference in energy levels of electrons in an occupied orbital and an other non occupied orbital, nothing happens. So the matter is transparant to that type of light (or more general electromagnetic radiation).

If however the difference corresponds to the energy of the photon, then an electron is promoted towards a higher energy level using the energy of the photon (which ceases to exist ).

The next question is : what happens to the electron with the extra energy?

It can do several things :

1. remain some time in this energy and then fall back to the previous level, emitting light of the same wavelength as the original (fluorescence)

2. fall back to some other energy level, emitting light of a longer wavelength thanthe original (fosforescence)

3. induce chemical reactions.

4. transfer this energy into heat.

Hope this helps.