2.1

2.1

1. 2.1.1.1 Atomic structure and isotopes

   • Atomic number=proton number
   • Mass number= nucleon number(protons and neutrons)
   • Isotopes are atoms of the same element with a different number of neutrons and therefore masses
     • The existence of isotopes was confirmed by mass spectroscopy which deflects ions in a magnetic field
     • Mass spectroscopy has 4 stages
       • 1-IONISATION: a sample is bombarded with electrons to produce a positive ion
       • 2-ACCELERATION: the ions is accelerated through and electric field
       • 3-DEFLECTION: the ion passes through a magnetic field to deflect it. Higher mass=less deflection.
       • 4-DETECTION: a sensor detects and records the ions reaching it
         • This stage produces a mass spectra graph. It shows the abundance against the m/z (mass/charge)
           • The number of peaks=the number of isotopes present
           • The height of each peak=percentage abundance

2. 2.1.1.2 Relative masses

   • Relative mass is not a way of measuring the mass of an atom as they are too small but a way of comparing them.
   • We compare the mass of atoms to 1/12th of the mass of a carbon-12 isotope which is taken to be exactly 12
     • Carbon-12 has 12 nucleons so 1-12 of this could be either a proton or a neutron
       • H had 1 proton so a relative mass of 1
       • Li has 7 nucleons (3p,4n) so a RM of 7
   • Relative isotopic mass: the mass of an isotope compared to 1/12 of the mass of an atom of carbon-12
   • Relative atomic mass: the weighted mean mass of an atom of an element compared to 1/12 of the mass of an atom of carbon-12
     • It is the weighted mean mass due to the presence of isotopes, it takes in to account the mass each isotope provides.

3. 2.1.2.1 formulae and equations

   • The charge of the ion is determined by the number of valance electrons that it can loose or gain
     • G1= 1 outer shell electron so +1
   • Common molecular ions: nitrate=NO3(-) Carbonate=CO3(2-) Sulfate=SO4(2-) Hydroxide=OH(-) Ammonium=NH4(+) Zinc=Zn(2+) Silver=Ag+
   • Stoichiometry is a balanced chemical equation that shows the quantitative relationship between each chemical
     • When ionic substances react, often, only a few ions are involved so an ionic equation is used instead
       • E.g. HCl+NaOH>NaCl+H2O
         • Only the hydrogen and hydroxide ions react. The others are spectator ions
           • H++OH->H2O

4. 2.1.3.1 moles and Stoichiometry

   • One mole is the amount of substance that contains as many particles as there are atoms in exactly 12g of carbon-12
     • The mass of a carbon-12 atom is approximately 1.99264*10^-23g
       • So the number of carbon atoms in 12g is X12 this much. Which is 6.022*10^23 atoms
         • This is Avogadro's constant. So one mole contains this many particles. No matter what substance it is
   • Molar mass: one mole of any substance will have a mass equal to the value of its molar mass due to the reletionship
     • Stoichiometric relationships: Stoichiometry can be used to determine the mole so/mass of a substance needed/formed during a reaction

5. Percentage yield and atom economy

   • Percentage yield
     • Stoichiometric relationships can be used to determine the theoretical amount of product formed during a reaction.
     • The % yield shows how much product actually formed compared to the theoretical amount
     • % yield=(product obtained/theoretical amount of product)X100
     • The higher the % yield the more efficient the reaction
   • Atom economy
     • This is becoming more important to industry as it considers the amount of waste being produced
     • Atom economy= (Mr of desired products/sum of Mr of all products)X100
       • Atom economy can be improved by finding uses for the unwanted products that are formed, thus making it more sustainable

6. 2.1.3.3 empirical and molecular formulae

   • Empirical formula is the simplest whole number ratio of elements within a substance
     • Molecular formulae shows the exact number of each element that is present within a substance

7. 2.1.3.3 water of crystallisation

   • It is the water contained within salt crystals
   • Hydrous salts contain water of crystallisation E.g. FeCl2•6H2O
     • Anhydrous salts lack water of crystallisation E.g.FeCl2

8. 2.1.3.5 Molar volumes

   • One mole of any gas at RTP will occupy a volume of 24p dm3
     • At standard conditions (STP 273K,100kPa) a One mole of gas will occupy a volume of 22.7dm3

9. 2.1.3.5 ideal gas equation

   • Ideal gases
     • They are gases that have molecules in random motion, no intermolecular forces present, elastic collisions so no exchange of kinetic energy and particles of zero volume
       • Real gases don't follow these conditions exactly but do get close at high temp or low pressures, but all gas equations assume they do
   • Gas volumes are directly linked to
     • Avogadro's law: higher moles=higher volume
     • Charles' law: higher temperature=higher volume
       • The ideal gas equation is PV=nRT
         • R is calculated at standard conditions to give 8.134Jmol-1K-1
           • p=101.32kPa
           • V=22.414dm3
           • N=1mol
           • T=273K
     • Boyle's law: higher pressure=lower volume
       • Combining these laws and adding the constant of proportionality you get the ideal gas equation

10. 2.1.3.7 Concentration

    • The concentration of a solution is a measure of the amount of solute dissolved within a volume of solvent
      • Solute-substance that has dissolved
      • Solvent-substance other chemicals dissolve in, usually water
      • The relationship between concentration and moles is: moles=concentration *volume, where v is in dm3 and c is in mol dm-3
      • Dilution
        • Dilution is often required so working out the dilution factor is needed
          • Dilution=original conc./diluted conc.
            • Once the dilution has been calculated the volume of original stock that is required can be determined
              • The remaining volume needed is given with distilled water
                • Original stock volume=total volume needed/ dilution

11. 2.1.4.1 Acids, bases, alkalis and neutralisation