Chemistry AS

Chemistry AS

1. The Atom

   • Three subatomic particles, proton, neutron and electron
     • Proton is positively charged with a relative mass of 1
     • Neutron has no charge with a relative mass of 1
     • Electron have a negative charge but has a relative mass of 1/2000
   • Usually have no charge overall but can be in the form of an ion or isotope
     • Isotopes are atoms of the same element but with a different numbers of neutrons
     • Ions have different numbers of electrons and protons
       • Lose and electron they become positive and vice versa if they lose an electron
     • The average of the isotopes found in the naturally occurring element id the relative atomic mass

2. Acids, Bases and Salts

   • Salts are either Anhydrous or Hydrated
     • Anhydrous salts refers to the pure non crytstal form
       • Sodium Sulfate
     • Hydrated salts have water molecules in their structure
       • Copper Sulfate
   • Most salts that exist in the solid form either as pure substances or in crystal form that contain water as part of their structure
   • Acids are proton donors, and release hydrogen ions into the solution
   • Bases accept protons, and when soluble in water, are called alkali, which release OH- ions into the solution
   • Acids and bases can be strong or weak
   • Salts are formed when a H+ ion from an acid has been replaced by a metal ion OR NH4
   • ACID + BASE = SALT + WATER

3. Gas Volumes

   • Gases take up the same volume under the same conditions
     • n=Volume in dm/Molar gas volume
     • Room temperature and pressure
   • Ideal gas equation
     • pV=nRT
       • p=Pressure (Pa)
       • V=Volume (m^3)
       • n=Number of moles
       • R=8.314 J K^-1 mol^-1
       • Temperature (K)
         • Celsius + 273

4. The Mole

   • Is just a number of particles
     • The Avogadro Constant
       • 6.02x10^23
     • N=m/M
       • m=Mass of substance
       • M=Molar mass
   • Molar mass is the mass of one mole
     • Molar mass is the same as the relative molecular mass
     • Units of 'Grams per mole'

5. Relative Mass

   • The masses of atoms compared to Carbon 12
     • Relative atomic mass, Ar, is the weighted mean mass of an atom of an element, compared to 1/12th of the mass of an atom of carbon 12
       • Can be worked out from the isotopic abundances
         • Work out the average mass of all its atoms, and then multiply the relative isotopic masses by its percentage abundance, then the sum divided by 100
     • Relative isotopic mass is the mass of an atom of an isotope, compared with 1/12th of the mass of an atom of carbon 12
       • Mass spectrometery can tell us a lot about isotopes
         • Multiply each relative isotopic mass by its relative isotopic abundance and make the sum if the results. The divide by the sum of the isotopic abundances
   • Relative molecular masses are the masses of molecules
     • This is the relative formula mass
     • The relative formula mass is the average mass of a molecule or formula unit compared to 1/12th the mass of an atom of carbon 12

6. Atomic Models

   • The accepted model of the atom has changed throughout history
     • Rutherford showed the plum pudding model was wrong
       • The Gold Foil Experiment
         • Shot alpha particles at very thin gold foil
           • Some were deflected backwards at not 90 degrees meaning the plum pudding model couldn't be right
       • Made the 'Nuclear Model'
   • Thompson did experiments showing atoms must have electrons, which he called corpuscles
     • What used to be solid spheres have been changed to the plum pudding model
   • Rutherford was then proved wrong by Moseley
     • Discovered that atoms nucleus' charge went up by one each time, finding the positive sub-particle, the proton
       • Neutron found by James Chadwick
   • Bohr model was a further improvement
     • Idea of shells to counter the collapsing theory
     • Explained why some atoms were inert
     • Not perfect but widely used today

7. Ionic Compound and Equations

   • Ions are made when electrons are transferred
     • simple ions either gain an electron or lose an electron to acheive a full outer
       • Charges in ionic compound always balance
     • Group 1 become 1+ ions, group 2 become 2+ and group 3 become 3+
     • Group 4 either loses or gains 4 electrons
     • Group 5 becomes 3-, group 6 becomes 2- an group 7 becomes 1-
     • Group 8 have no ions as they're inert
   • Not all ions are made from single atoms
   • Salts are ionic compounds
     • All solid salt consist lattice of positive and negative ions
     • Many salts lose their water molecules when heated

8. Concentration Calculations

   • C1 x V1 = C2 x V2
   • Concentration = Number of moles/Volume
   • Mol dm^-3