General Chemistry/Measurement
MolesEdit
The mole is a unit used to measure the number of particles in a substance (where particles can be atoms, molecules, electrons, ions etc.). One mole of substance contains 6.02205 × 10^{23} particles. This rather large quantity is a constant called Avogadro's Number, which is abbreviated as N_{A}. It simply refers to the number of particles in one mole.
For example, one mole of helium gas contains 6.022×10^{23} atoms; 2 moles of oxygen gas contains 1.204×10^{24} molecules.
Moles and MassEdit
It would be useful to be able to convert between the number of moles and the mass of a substance. The molar mass is the mass of one mole of a substance, measured in grams per mole or . Not by coincidence, the molar mass is the same as the atomic weight of a substance (this is how the concept of moles was originally defined).
For example, the molar mass (and atomic weight) of carbon12 is 12 g·mol^{−1}, so 1 mole of carbon12 weighs 12 grams. Similarly, chlorine has a molar mass of 35.45 g·mol^{−1}, so one mole of chlorine atoms weighs 35.45 g. There are two chlorine atoms in one molecule of Cl_{2} gas, so one mole of Cl_{2} gas weighs 70.90 g.
Measurement and QuantitiesEdit
See the Units Appendix for tables of SI fundamental and derived units.
Commonly used units in ChemistryEdit
QuantityEdit 
Commonly used units and symbolsEdit 
Conversions (etc)Edit 
amount of substance 
mole, mol 
1 mol = 6.022×10^{23} particles 
concentration (solutions) 
mole per litre, mol L^{1} 
(mol L^{1})(g mol^{1}) = g L^{1} 
electric charge 
coulomb, C 

electric current 
ampere, A 

electromotive force 
volt, V 

energy 
joule, J

1000 J = 1 kJ 
density 
gram per litre, g L^{1} 

mass 
gram, g

1 tonne = 1000 kg = 1×10^{6} g 
molar volume 
litre per mole, L mol^{1} 
22.41 L (S.T.P) 
pressure 
kilopascal, kPa

1 atm = 101.324 kPa = 760.0 mmHg 
temperature 
kelvin, K

T_{K} = T_{C} + 273.15 
time 
second, s

1 h = 3600 s 
volume 
litre, L

1 L = 1000 mL = 1 dm^{3} = 1000 cm^{3} 
Commonly used prefixesEdit
PrefixEdit 
SymbolEdit 
FactorEdit 
tera 
T 
10^{12} 
giga 
G 
10^{9} 
mega 
M 
10^{6} 
kilo 
k 
10^{3} 
milli 
m 
10^{−3} 
micro 
µ 
10^{−6} 
nano 
n 
10^{−9} 
pico 
p 
10^{−12} 