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First of all, I hardly know any chemistry, so let's get that out of the way.

I have been wondering lately, from a "common sense" point of view (owing to my lack of knowledge), that since air cannot be seen and yet is considered as being made up of elements, then what precludes us from considering things like x-rays and radio waves to be elements? What precludes the electromagnetic spectrum from being considered an element? What about light and gravity, or the four fundamental forces?

If someone could kindly elucidate the differences between these categories of "thing", I would highly appreciate it and it would remove much confusion that I have been experiencing lately.

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    $\begingroup$ They don't make anything what was considered a substance ages ago, so they aren't elements. $\endgroup$ – Mithoron Jul 11 '17 at 16:23
  • $\begingroup$ Element is a wrong word, but you could useparticle? That in fact, is a quite known fact: de Broglie wave-particle duality. $\endgroup$ – Pritt says Reinstate Monica Jul 11 '17 at 16:25
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    $\begingroup$ I'd argue that to be a proper chemical element, a "thing" must have rest mass, which would exclude photons. $\endgroup$ – iammax Jul 11 '17 at 16:27
  • $\begingroup$ Photons are NOT considered matter because they have no mass, since they don't interact with the Higgs field in a way the gives rise to mass. Since they don't have mass, they can't combine to give ordinary matter. $\endgroup$ – Zhe Jul 11 '17 at 16:28
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    $\begingroup$ Elements just refer to classification of matter based on atoms. Anything else is not an element. Otherwise, as you can tell from comments, you can really go off the rails in a non-helpful way... :) $\endgroup$ – Zhe Jul 11 '17 at 21:50
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I like your approach. "Here's the way I see the categories of 'elements' and 'not elements.' Why don't they draw the line this way?" While the line you want to draw to include "rays" alongside the elements that appear in the air isn't the one science draws, it does point out something really important: We draw the lines between categories because they are useful.

As it turns out, the differences in behaviors between "things" like hydrogen atoms and helium atoms, and "rays" like radio and X-rays is substantial as you dig further into science. The "elements," for instance, are "massive," meaning they have mass. Quantum scientists would say they "interact with the Higgs field." However, you choose to phrase it, these atoms behave very differently than electromagnetic waves (which is the proper term for "rays"). Electromagnetic waves have no mass (other than some secondary effects that you'll learn when you study relativity). Their propagation through space is well defined by Maxwell's Equations. They don't form bonds (like most elements do). They don't take up space (electromagnetic waves don't push each other away, but atoms can only get so close before the repulsive forces drive them apart).

Eventually, you will learn that the lines blur. Relativity will start to explain why electromagnetic waves indeed do have mass. Quantum Mechanics will point out that particles have wave-like properties. However, as you start out, the differences between "massful things" and "electromagnetic waves" is pretty iron clad. As you continue your studies, you'll become more comfortable with the distinctions drawn, and then we can slowly introduce all those strange line-blurring facets of our reality that makes science really interesting.

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