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

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

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

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

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

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

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

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

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

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

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

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

or there are other things that can be liquid,

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

if you raise the temperature high enough on Gold or Lead

you could get a liquid,

Or if you kind of - if you burn this Carbon

you can get it to a gaseous state,

you can release it into the atmosphere,