- 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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- 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 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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- 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
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- 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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