Atoms & Reactions

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  • Created by: ernily
  • Created on: 09-04-15 16:12

The Atom

  • Atoms make up elements and compounds.
  • They are made up of protons, neutrons, and electrons.
    • Electrons have a -1 charge & a relative mass of 1/2000.
    • They move around the nucleus in orbitals.
    • Protons have a +1 charge and a relative mass of 1.
    • Neutrons have 0 charge and a relative mass of 1.
  • Mass Number: The total number of protons and neutrons in the nucleus.
  • Atomic Number: The number of protons in the nucleus.
  • Negative ions have more elctrons than protons.
  • Positive ions have fewer electrons than protons.
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The Atom

  • Isotopes are atoms of the same element with different numbers of neutrons.
  • Isotopes have the same electron configuration, and so have the same chemical properties.
  • They have slightly different physical properties due to their mass.
  • Different mass numbers = different number of neutrons.
  • Their atomic numbers are the same.
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Relative Mass

  • Relative Atomic Mass (Ar): The average mass of an atom of an element on a scale where an atom of carbon-12 is 12.
  • Relative Isotopic Mass: The mass of an atom of an isotope of an element relative to one twelfth of an atom of carbon-12.
  • Relative Molecular Mass (Mr): The average mass of a molecule relative to one twelfth of an atom of carbon-12.
  • Isotopic Abundances:
    • Multiply each relative isotopic mass by its % relative isotopic abundance, then add up the results.
    • Divide by 100.
  • IF IN A GRAPH:
    • Multiply each relative isotopic mass by it's relative isotopic abundance, then add up the results.
    • Divide by the sum of the abundances.
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The Mole

  • A mole is just a number of particles.
  • Avagadro Constant, Na - 6.02 x 1023
  • n = m / Mr
  • Molar Mass is the mass of one mole.
  • In a solution, the concentration is measured in mol dm-3
  • n = concentration x volume 
  • OR n = (conc. x vol [in cm3]) / 1000
  • All gases take up the same volume under the same conditions.
  • n = v / 24
  • OR n = v [in cm3] / 24000
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Empirical & Molecular Formulas

  • Empirical Formula: The smallest whole number ratio of atoms in a compound.
  • Molecular Formula: The actual number of atoms in a molecule.
  • Both are calculated from experimental data.
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Equations & Calculations

  • Balanced equations have the same number of each atom on both sides.
  • In ionic equations, the charges must balance.
  • Balanced equations can be used to work out masses and gas volumes.
  • State symbols give more information about the substances.
  • e.g.: CaCO3 (s) + 2HCl (aq) --> CaCl2 (aq) + H2O (l) + CO2 (g)
  • s = solid
  • aq = aqueous solution
  • g = gas
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Acids, Bases & Salts

  • Acids are proton donors.
  • Bases are proton acceptors.
  • Acids react to form neutral salts:
    • H2SO4 produces sulfates.
    • HCl produces chlorides.
    • HNO3 produces nitrates.
  • Acids react with bases; they neutralise each other.
  • Alkalis are soluble bases;
    • NaOH: Sodium Hydroxide.
    • KOH: Potassium Hydroxide.
  • Metal Oxide + Acid --> Salt + Water
  • Metal Hydroxide + Acid --> Salt + Water
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Acids, Bases & Salts

  • Salts can be anhydrous or hydrated.
  • Water of Crystallisation: Water in a lattice
  • EXAMPLE: Heating 3.210g of MgSO4.XH2O forms 1.567g of MgSO4. Find X.
  • n(H2O lost): 3.210 - 1.567 = 1.643 / 18 (Mr) = 0.0913mol
  • n(MgSO4) = 1.567 / 120 (Mr) = 0.0131mol
  • 0.0131 : 0.0913
  • 0.0131 / 0.0131 = 1                     Divide by smallest number
  • 0.0913 / 0.0131 = 7
  • Ratio = 1:7
  • MgSO4.7H2O
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Titrations

  • Titrations allow you to find out exacly how much acid is needed to neutralise a quantity of alkali.
  • Measure out some alkali using a pipette and put it in a flask along with some indicator.
  • Do a rough titration to find the end point.
  • Then do an accurate titration.
  • Indicators show you when the reaction is just finished.
  • Methyl Orange: Yellow --> Red.
  • Phenolphthalein: Pink --> Colourless.
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Oxidation & Reduction

  • If electrons are transferred, it is a redox reaction.
  • Loss of electrons is oxidation.
  • Gain of electrons is reduction.
  • Oxidising agents accept electrons and are reduced.
  • Reducing agents donate electrons and are oxidised.
  • Oxidation Numbers:
    • All atoms are treated as ions.
    • Uncombined elements have an oxidation number of 0.
    • Elements bonded to identical atoms have an oxidation number of 0.
    • The oxidation number of a monatomic ion is the same as it's charge.
    • In compounds, the overall oxidation number is just the ion charge.
    • Sum of oxidation numbers for a neutral compound is 0.
    • Combined oxygen = -2.
    • Combined hydrogen = +1.
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Oxidation & Reduction

  • You can work out oxidation numbers from formulas or systematic names.
    • Sulfate (VI) = +6 on sulfur --> SO4 2-
    • Sulfate (IV) = +4 on sulfur --> SO3 2-
  • Oxidation numbers go up or down as electrons are lost or gained.
    • Increase by 1 for each electron lost.
    • Decrease by 1 for each electron gained.
  • Many metals reduce dilute acids.
  • Metal atoms are oxidised, hydrogen ions are reduced.
  • Sulfuric acid is disproportionation; both oxidised and reduced.
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