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We Humans have known for thousands of years, just looking at our environment around us that

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there are different substances, and these different substances tend to have different properties, and

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not only do they have different properties; one might reflect light in a certain way, or not reflect light

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or be a certain colour, or at certain temperature be liquid, or gas, or be a solid,

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but we also start to observe how they react with each other in certain circumstances.

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And here's pictures of some of these substances. This right here is Carbon, and this is in it's graphite form;

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this right here is Lead, this right here is Gold,

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and all of the ones that I've drawn, that I've shown pictures of here, and I got them all from this website right over there

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all of these are in their solid form, but we also know that

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it looks like there's certain types of air, you know, certain types of air particles,

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and depending on what type of air particles you're looking at

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whether it is carbon, or oxygen, or nitrogen, that seems to have different types of properties,

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or there are other things that can be liquid,

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or even if you raise the temperature high enough on these things,

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if you raise the temperature high enough on Gold or Lead

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you could get a liquid,

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Or if you kind of - if you burn this Carbon

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you can get it to a gaseous state,

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you can release it into the atmosphere,