Atomic Structure

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Isotopes & Mass

  • Have the same atomic number but different atomic mass numbers
  • Same number of protons and electrons but a different number of neutrons
  • React in the same way because they have the same electronic configuration

Relative Atomic Mass (A  )= Mass of the element:

  • carbon = 12
  • Oxygen = 16
  • Magnesium = 24

Relative Formula Mass (M  )= Mass of the compound:

  • NaCl- Sodium Chloride = 23 + 35.5 = 58.5
  • Al  O  - Aluminium Oxide = (2 x 27) + (3 x 16) = 102
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% Composition & Moles

% Composition: A  / M   x 100:

  • % of Cu in CuSO   = 63.5 / 159.5 x 100 = 39%
  • % of Na in NaOH = 23/ 40 x 100 = 57%

Moles: The number of atoms in the amount of frams of it's A  :

  • Carbon = 12g
  • Chlorine = 35.5g
  • Potassium = 39g
  • This number is 6.02 x 10^23 - Avogardo's constant
  • 1 mole of a compound if it's M 
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Empirical Formula

The simplest whole number ratio of each atom in a compound:

  • CuSO   = 1 Copper , 1 Sulfur , 4 Oxygen

To work out the ratio:

  • Find the masses/ percentages (Usually given inthe question)
  • Look up Ar value from periodic table
  • Divide mass by Ar
  • Ratio
  • Formula = SO
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% Yield & Gas Chromatography

  • % Yield = Actual Yield / Theoretical Yield x 100
  • Shows us how much is actually made compared to the prediction
  • A high % yield means that money is saved and less resources are wasted

Gas Chromatography:

  • Sample is dissolved in a solvent. then injected into one end of a column
  • An unreactive gas carries the sample through the column
  • Different substances in the sample travel through the column at different speeds and so become seperated from each other 
  • The seperated substances leave the column one after the other. As they leave, they are detected by a detector
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