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I know electrons are subatomic particles which make up atoms, the building blocks of matter. But is electron a matter itself? Moreover, are atoms or quantum particles matter too considering their particle nature for now?

Urb
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user39499
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    Except for massless particles like photons, every other particle and their combination is called matter. – Paul Mar 11 '21 at 05:54
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    whyd don't you look up the definition of "matter" in wikipedia, https://en.wikipedia.org/wiki/Matter – anna v Mar 11 '21 at 06:24

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As Wikipedia says:

In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume.

Electrons are fermions, that is, elementary particles, that is, with no substructure.

A point particle is different from an elementary particle :

In quantum mechanics, the concept of a point particle is complicated by the Heisenberg uncertainty principle, because even an elementary particle, with no internal structure, occupies a nonzero volume.

Therefore, electrons have mass and volume, hence electrons are matter.

David
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    I like your logic, but I think using the H.U.P. to assert that electrons have volume is a stretch. The quote you present asserts that electrons occupy a volume, which could mean a few different things depending on your your philosophical interpretation of quantum mechanics. It does not guarantee that electrons are not point particles with zero size that simply have a specific volume associated with the probability of locating them. If the electron actually possesses a nonzero volume like you assert, we would be able to assign a mass density to it. I am not aware of such a thing. – electronpusher Mar 11 '21 at 13:36
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    Here thread that shines light on whether an electron can be said to have a mass density/occupy a volume. The answer is if the electron does have a radius, it is not bigger than $10^{-22}$, and it behaves as a point particle in every experiment to date. https://physics.stackexchange.com/q/24001/139376 I think ultimately the answer to whether an electron is "matter" is an issue of semantics. I think we can all agree the electron is a "matter particle" or "particle of matter" (unlike the photon). – electronpusher Mar 11 '21 at 13:45
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Light (photons) doesn't have a mass. Particles that move slower than light have a property called rest mass. These particles can exist without moving around. But they still have energy given by Einstein's famous equation E=mc^2. Light waves with enough energy can crash into a sheet of lead and change into positive and negative charges with mass like electrons and positrons. By Einstein's equation light energy becomes mass. A useful way to think of energy and mass is that energy is water vapour and mass is drops of water. They are the same and different.