Element, Atom, Compound, Molecule:
An element
is a substance which contains only one kind of atom: lead (Pb), silver
(Ag), hydrogen (H2), oxygen (O2).
An atom
is the smallest particle of an element which exhibits the physical and chemical
characteristics of that element.
A compound
is a substance which contains two or more kinds of atoms: carbon dioxide
(CO2), calcium oxide (CaO), sodium hydroxide (NaOH).
A molecule
is the smallest particle of a substance which exhibits the physical and chemical
characteristics of that substance.
Monoatomic
molecules of elements - Cu, Ag, Na, etc.
Multiatomic
molecules of elements - H2, N2, O2, F2,
Cl2, Br2, I2, P4, S8
Molecules of compounds -
Na2O, KOH, CaSO4, HBr, H2CO3
Examples:
double the answer and p
(contain an unlimited number of
decimal places)
Special case - when some zeros are
significant and some are not, use a line to show which ones are.
Examples:
3400 (3 sig fig) 2000 (3 sig fig)
Composition and Uses of Some Alloys
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