Quantifying Chemistry and The Mole

I really struggled to understand this topic, so I have put together this handy guide to the Mole, of what I would have found helpful as I tried to figure out what all of this meant.
 Atoms are really small, so we cannot measure them using cm or even mm, grams or milligrams. Nothing we would use in everyday life would be practical to measure their mass or length. 

 A mass spectrometer is used to split elements into isotopes of different masses. 

 The term mole (mol) represents a number, in the same way the word dozen does. However, dozen means twelve, and mole means 6.02 x 1023 

 This is known as Avogadro's Number, and is equal to the number of atoms in 12 grams of Carbon-12. Mole is not mass, so one mole of different substances will each have different masses, but the same number of particles (6.02 * 1023 )


That's really all the theory needed for the Mole, however, you will be asked most likely to do a number of calculations using this knowledge.

Determine molar mass (M) : The mass of one mole of the element, that is 6.02 * 1023 )atoms. The unit is grams per mole (g mol−1).

To find the mass of one mole of an element, simply add ‘g’ to the relative atomic mass of that element. 

For atoms: molar mass is equal to the atomic mass, so one mole of any element is equal to its atomic mass. 
Eg. 1 mole of carbon (6.02 × 1023 atoms) has a mass of 12.0 g.


For ionic compounds: the molar mass is found by adding the atomic mass of each atom in the formula of the compound.
Eg. Mr(CuSO4) = Ar(Cu) + Ar(S) + (4 × Ar(O))

= 63.5 + 32.1 + (4 × 16.0)
= 159.6g mol-1


For molecular compounds: the molar mass is equal to the molecular mass.
Eg. Molar mass of water molecules = mass of 1.00 mol of H2O molecules
= (2*1) + (1*16)
= 18.0 g mol−1
∴ 18.0 g of water contains 6.02 × 1023 molecules of water.

Convert Mass to Moles and Moles to particles

Eg. How many atoms in 10moles of helium?   10 x 6.02 × 1023 = 6.02 × 1024 
How many mole in 3.01 × 1023 helium atoms?   
=> (6.02 × 1023 ) divided by (6.02 × 1023) = .5 moles

Relative Isotopic Mass: RIM: the mass of a single isotope and is determined by comparing the mass of ions of the isotope to carbon-12. One element may have multiple RIM.

Relative Atomic Mass: Ar: represents the average mass of one atom, taking into consideration the number of isotopes of the element, their relative isotopic mass (RIM) and their relative abundance. Each element has only one RAM.

Relative Molecular (or Formula) Mass: Mr: of a molecule is the sum of the relative atomic masses, as shown in the periodic table, of elements in the formula.

Percentage Composition:
The percentage by mass of each element present within a compound: 


Empirical Formula
The simplest whole number ratio of atoms or ions present in a compound. To determine the empirical formula of a compound, an experimentally determined ratio of elements by mass must be converted to a ratio of elements by numbers. This is done by calculating the number of moles of each element.


Steps: 
1. Symbols: Write out symbols of elements in compound
2. Masses: Write the mass present (if expressed in percentages, just write this directly as grams - 2.4% 
becomes 2.4g - under each corresponding element)
3. Moles: divide the mass present by the molar mass.
4. Ratio: divide the answer above by the smallest result to give a ratio.











The Empirical Formula = Ionic Formula
The Empirical Formula doesnotalways= The Molecular Formula

The Molecular Formula:
the actual number of atoms that are present in a molecule of that substance. 
It can be equal to the empirical formula, or it can be a whole number multiple of the empirical formula.
Note: Note that only molecular compounds can have a molecular formula.


n × (empirical formula) = molecular formula

Example: Glucose
C6H12O6 = molecular
CH2O = empirical


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