# Atoms & Reactions

• 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.
• 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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