Chemistry

• Structure of atoms: Atoms are made up of three different subatomic particles - protons, neutrons and electrons
• Protons

  In the nucleus, have a mass of 1 and a charge of +1
• Neutrons

  In the nucleus, have a mass of 1 and a charge of 0
• Electrons

  Found in the outer shells, have a very small mass (1/1836 of a proton) and a charge of -1
• The actual charge of protons, neutrons and electrons is very small but it is easier to express as +1, 0 and -1 respectively
• The diameter of the nucleus is 10^-15 m whereas the diameter of the whole atom is 10^-10 m, so the atom is mostly empty space
• The structure of the atom has changed over time as new evidence has presented itself
• Mass number

  The total number of protons and neutrons in an atom, shown as the larger number on the periodic table
• Atomic number

  The number of protons in an atom, shown as the smaller number on the periodic table
• Isotopes are different versions of the same element with the same atomic number but different mass numbers
• Time-of-flight mass spectrometry

  1. Unknown sample mixed with polar solvent

  2. Ionisation by electrons or spraying

  3. Acceleration by electric field

  4. Heavier ions go slower

  5. Detector measures mass-to-charge ratio
• Relative atomic mass

  The average mass of an atom of an element compared to 1/12 the mass of a carbon-12 atom
• The structure of the atom we are used to drawing is not accurate, we need to look at shells, subshells and orbitals
• Blocks of the periodic table

  • s-block
  • p-block
  • d-block
  • f-block
• Electron configuration

  The arrangement of electrons in an atom's shells, subshells and orbitals
• Ions

  Atoms that have lost or gained electrons
• First ionization energy

  The energy required to remove one electron from each atom in a mole of gaseous atoms
• Second ionization energy

  The energy required to remove one electron from each ion in a mole of gaseous positive ions
• Factors affecting ionization energy include atomic radius, electron shielding/repulsion, and nuclear charge
• Trends in successive ionization energies show a big jump between the 7th and 8th electrons due to a new shell starting
• Ionization energy data can provide evidence for electron configuration
• Significant figures

  The number of meaningful digits in a measurement or calculation
• Converting between units

  1. Celsius to Kelvin: add 273

  2. Centimetres cubed to metres cubed: divide by 1,000,000

  3. Grams per litre to moles per litre: divide by molar mass
• Relative molecular mass

  The average mass of a molecule compared to 1/12 the mass of a carbon-12 molecule
• Mole

  The amount of a substance that contains the same number of particles as the number of carbon-12 atoms in 12 grams
• Avogadro's number

  The number of particles in a mole, 6.02 x 10^23
• Balancing chemical equations

  Draw circles around the equations

  2. List what you have on each side

  3. Adjust the numbers to balance atoms
• Equations using moles

  • Ideal gas law: PV = nRT

  Concentration of solutions: n = CV

  Mass: n = m/Mr

  Number of particles: n = N/NA
• Concentration is measured in grams per cubic decimetre
• For ionic solutions and acidic solutions, the number of moles of ions produced is not 1:1 with the number of moles of the compound
• Making a standard solution and titration

  Weigh out powder accurately

  2. Dissolve in water and wash container

  3. Titrate against another solution
• Ionic solutions

  There are two different ions, e.g. calcium two plus and two chlorine ions. From one mole of calcium chloride we get one mole of calcium ions but two moles of chloride ions.
• Acidic solutions

  For every one mole of sulfuric acid we will end up with two moles of hydrogen ions.
• Making a standard solution

  1. Weigh out powder into water

  2. Continuously wash weigh boat to get all powder into beaker

  3. Wash sides of beaker to get all powder in

  4. Fill flask to required volume

  5. Invert to mix properly
• Making a standard solution

  • Need to be very accurate
  • Do not go over the final volume, if you do don't remove any
• Titration

  1. Do a rough titration first

  2. Aim for 3 concordant results (within 0.10 cm3 of each other)

  3. Record results to 2 decimal places
• Titration calculation

  1. Highlight all information in the text

  2. Pull out the volume of acid, concentration of acid, volume of alkali, concentration of alkali

  3. Write down the balanced equation
• Titration calculation

  1. Find moles of known (acid)

  2. Find ratio of ions

  3. Use moles, concentration, volume to find concentration of alkali

  4. Convert units to required format (e.g. g/dm3)
• Ideal gas law

  PV = nRT, where P is pressure, V is volume, n is moles, R is gas constant, T is temperature
• Ideal gas law calculation

  1. Highlight all numbers in the question

  2. Convert non-standard units to standard units

  3. Use PV = nRT to find number of moles

  4. Use mass = moles x Mr to find mass