Stoichiometry and the Mole Concept
element symbols
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Each element is represented by its own unique symbol
Where a symbol contains two letters, the first one is always in capital letters and the other is small
Atoms combine together in fixed ratios that will give them full outer shells of electrons
The chemical formula is what tells you the ratio of atoms
The chemical formula can be deduced from the relative number of atoms present
Diagrams or models can also be used to represent the chemical formula
chemical formula
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The structural formula tells you the way in which the atoms in a particular molecule are bonded. This can be done by either a diagram (displayed formula) or written (simplified structural formula)
The empirical formula tells you the simplest whole-number ratio of atoms in a compound
The molecular formula tells you the actual number of atoms of each element in one molecule of the compound or element
names of compounds
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If one is a metal and the other a nonmetal, then the name of the metal atom comes first and the ending of the second atom is replaced by adding –ide
If both atoms are nonmetals and one of those is hydrogen, then hydrogen comes first
For other combinations of nonmetals as a general rule, the element that has a lower Group number comes first in the name
balancing equations
use the chemical symbols of each reactant and product
When balancing equations, there needs to be the same number of atoms of each element on either side of the equation
The following nonmetals must be written as molecules: H2, N2, O2, F2, Cl2, Br2 and I2
Work across the equation from left to right, checking one element after another
balancing ionic eq
In aqueous solutions ionic compounds dissociate into their ions, meaning they separate into the component atoms or ions that formed them
Write out the full balanced the equation
Identify the ionic substances and write down the ions separately
Rewrite the equation eliminating the ions which appear on both sides of the equation
the mole
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This is the mass of a substance containing the same number of fundamental units as there are atoms in exactly 12.000 g of 12C
The mole is the unit representing the amount of atoms, ions, or molecules
One mole is the amount of a substance that contains 6.02 x 1023 particles (Atoms, Molecules or Formulae) of a substance (6.02 x 1023 is known as the Avogadro Number)
One mole of any element is equal to the relative atomic mass of that element in grams
For example one mole of carbon, that is if you had 6.02 x 1023 atoms of carbon in your hand, it would have a mass of 12g
molar volume
This is the volume that one mole of any gas (be it molecular such as CO2 or monoatomic such as helium) will occupy
It’s value is 24dm3 or 24,000 cm3 at room temperature and pressure (r.t.p.)
empirical formula
gives the simplest whole number ratio of atoms of each element in the compound
Calculated from knowledge of the ratio of masses of each element in the compound