Basic Chemistry Stuff

I am taking an Earth Science course now and currently reviewing some basic chemistry knowledge needed for further study on earh mineral and rocks. But I haven't touched chemistry for almost 2 years that I start to forget things, can someone help and clarify some basic chemistry stuff? I would appreciate! :wink:

1) Are the terms "element" and "atom" interchangeable? If not, why not?

2) Do the terms "substance" and "matter" mean exactly the same thing?

3) "Two of the eight common elements in the earth's crust are oxygen (O) and silicon (Si)"
http://inst.sfcc.edu/~gmead/minerals/crustal.gif

Why is oxygen expressed as O, instead of O2, in both the quote and diagram? Does that mean single O atom exist naturally in the crust?

4) Compound: a substance that results when the atoms of two or more elements are chemically combined
This is the definition of a "compound" from my text book and it's the same as all sources in the internet. According to the definition of a compound, O2 and N2 are not compounds, than what are they? elements?

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Originally Posted by kingwinner

1) Are the terms "element" and "atom" interchangeable? If not, why not?

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No. An element is a discrete species of an atom and would have specific characters. An atom is the description of the basic structure of an element. The nature of the atom (number of electrons, protons, etc.) define the type of element it is.

Quote:

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Originally Posted by kingwinner

2) Do the terms "substance" and "matter" mean exactly the same thing?

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I would think so. The usage of one or the other would depend largely on context. You wouldn't say "a matter" comprised of... but you could say "a substance comprised of..." The word 'matter' would likely be used in contexts of mass whereas 'substance' would be used in contexts of characteristics.

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Originally Posted by kingwinner

3) "Two of the eight common elements in the earth's crust are oxygen (O) and silicon (Si)"

Why is oxygen expressed as O, instead of O2, in both the quote and diagram? Does that mean single O atom exist naturally in the crust?

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O₂ is a diatomic molecule of oxygen, whereas O is the element/atom that is known as oxygen. The graph represents oxygen as "O" because not all the oxygen on the Earth is part of diatomic molecules. A good portion of it is tied up in other molecules (H₂O, for instance).

Quote:

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Originally Posted by kingwinner

4) Compound: a substance that results when the atoms of two or more elements are chemically combined
This is the definition of a "compound" from my text book and it's the same as all sources in the internet. According to the definition of a compound, O2 and N2 are not compounds, than what are they? elements?

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They're diatomic molecules, or two atoms, of a single element. NO₂, however, is a compound.


I'm sure someone else could expand upon my words... I'm going completely off of memory. I had a dynamite chem professor and learned a lot, but I really didn't have a knack for it.

4) A compound is a substance that results when the atoms of two or more elements are chemically combined
A molecule is the smallest unit of a compound that still retains its properties.

If the above 2 definitions are both true, than O2, H2, N2 are all not (diatmoic) molecules, since they do not meet the requirement that "two or more elements", each of O2, H2, N2 has only one element chemically combined?! But why are they always referred to as diatmoic molecules?

They're molecules, they just aren't compounds.

1. No, an atom is smallest part of an element that still has the same properties of an element. Atoms are specific elements, but a bunch of atoms with the same atomic number will be one element.

2. They are kinda the same thing. Usually a substance is used when you are not sure what it is, and matter is everything (exept antimatter).

3. O2 is 2 oxygen atoms, bonded together into a compound. O is an element.

4. I think that O2 is a compound (I am pretty sure). It is called diatomic, because it is the same element bonded together, but the entire structure changes when they bond. It is not just 2 O atoms stuck together.

I am taking Chem right now though, so don't take this as gospel