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
• Atomic number


  The number of protons in an atom
• 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. Smaller ions go faster

  5. Detector measures ions creating small charge
• Mass-to-charge ratio (m/z)


  The ratio of the mass of an ion to its charge, used to determine the relative mass
• The mass number on the periodic table is the average of all the naturally occurring isotopes of an element
• The structure of the atom we are used to drawing is not accurate, we need to look at the shells, subshells and orbitals
• Blocks of the periodic table


  • s-block
  • p-block
  • d-block
  • f-block
• Atomic orbitals


  Can be spherical (s), dumbbell-shaped (p), or more complex shapes (d, f)
• Ions are atoms that have lost or gained electrons to achieve a noble gas configuration
• First ionization energy


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


  Energy required to remove one electron from each ion in a mole of gaseous positive ions
• Factors affecting ionization energy: atomic radius, electron shielding/repulsion, nuclear charge
• Trends in successive ionization energies: big jump between electrons 7 and 8, increases across periods, sharp drop between periods
• Ionization energy can provide evidence for electron configuration
• Significant figures


  The number of digits in a measurement that are known with certainty
• Converting 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


  Average mass of a molecule compared to 1/12 the mass of a carbon-12 atom
• Relative atomic mass


  Average mass of an atom compared to 1/12 the mass of a carbon-12 atom
• 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 in the same order

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


  • Ideal gas law: PV = nRT

  Concentration of solutions: n = CV

  Mass: n = m/M

  Number of particles: n = N/N_A
• For ionic solutions and acidic solutions, the number of moles of ions produced is not equal to the number of moles of the compound
• Making a standard solution and titration


  1. Weigh out powder accurately

  2. Dissolve in water and wash sides of 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 get 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
• When doing a titration calculation, highlight all the information in the text and pull it out separately
• Titration calculation


  1. Write balanced equation

  2. Find moles of known (acid)

  3. Find ratio of ions

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

  5. 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