ATOM - The smallest particle of an element which can take part in a chemical change.
OPERATIONAL DEFINITION ( O.D.) They give general directions for a laboratory procedure to determine whether a substance is an element or a compound.
CONCEPTUAL DEFINITION ( C.D.) Tells how to think about the item in question rather than how to identify it in practice.
C. D. - Element - A substance which is made of the same kind of atoms.
O. D. - Element - The simplest form of matter that cannot be decomposed any further by ordinary chemical means.
C.D.- Compound - Substance containing two or more different kinds of atoms.
O.D. Compound - A substance that is made up of two or more elements chemically combined, that can be decomposed by ordinary chemical means.
Pure substances are either compounds or elements.
Molecules - Atoms or all groups of atoms, that formed discrete particles.
Monatomic Molecules ( Single atoms )
Example:
Argon, Krypton, Xenon, Radon, Helium and Neon ( All are elements )
Diatomic Molecules ( Two atoms )
Compounds
Examples: CO, ( carbon monoxide ); HgO, ( mercuric oxide ); HCl ( hydrochloric acid )
Elements
Examples: H2, O2, N2, Cl2
Size
Ordinary Gas Molecules could have a size of 3 x 10-8 cm.
Gas Molecules are measured in Angstrom Units, (A°) . ( the ° is situated on top of the letter A )
1 A° = 1 x 10 -8 cm
3 x 10 -8 cm = 3 A°
A large molecule could be about the size of 230 A° .
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