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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