Whole 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. Smaller ions go faster

  5. Detector measures ion charge
• Mass-to-charge ratio (m/z)

  The ratio of an ion's mass to its charge, measured by a mass spectrometer
• The average mass of naturally occurring isotopes of an element is the relative atomic mass shown on the periodic table
• 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
• 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 1 mole of gaseous atoms
• Second ionization energy


  Energy required to remove one electron from each ion in 1 mole of gaseous +1 ions
• Factors affecting ionization energy: atomic radius, electron shielding/repulsion, nuclear charge
• Trends in ionization energy: increases across periods, sharp drop between periods
• Ionization energy provides 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. Moles to grams per litre: multiply 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 containing the same number of particles as there are atoms in 12 grams of carbon-12
• Avogadro's number


  The number of particles in 1 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
• Equations using moles


  • Ideal gas law: PV = nRT

  Concentration of solutions: n = cV

  Mass: n = m/Mr

  Number of particles: n = N/NA
• Concentration


  Measured in grams per cubic decimetre (g/dm^3)
• For ionic solutions, the number of moles of ions is not equal to the number of moles of the compound
• For acidic solutions, the number of moles of hydrogen ions is equal to the number of moles of the acid
• 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 into flask

  4. Fill flask to required volume

  5. Invert to mix thoroughly
• Importance of accuracy when making a standard solution


  • Do not go over the volume mark, if you do, you have to start again as removing some would change the concentration
  • Take care on every step as there are many potential sources of error
• Titration


  1. Do a rough titration first to get an estimate

  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 so it's easy to find later