Key Terms

• Isotope

  Atoms of the same element with the same atomic number but with different number neutrons, resulting in different mass number.
• Mass Number


  Number of neutron and protons added together.
• Atomic Number


  Proton number.

  Can determine chemical properties of an element and its place in the periodic table.
• John Dalton (1803) 


  [+] recognised atoms of a particular element differ from other elements

  [-] atoms are not indivisible, they’re composed from subatomic particles
• JJ Thompson (1897-1904)


  [+] discovery of the electron

  [-] no nucleus, electrons are not embedded on a positive ball
• Rutherford (1911)

  [+] realised positive charge was localised in the nucleus of the atom

  [-] did not explain why electrons remain in orbit around the nucleus
• Niels Bohr (1913)


  [+] proposed stable electron orbits

  [-] moving electrons should emit energy and collapse into the nucleus model, didn’t work well for heavier atoms
• Erwin Schrödinger (1926) 


  [+] shows electrons do not move around the nucleus in orbitals but in clouds where their positions is uncertain

  [-] still widely accepted as it is the most accurate model of the atom
• Electron Configuration of anomalies Cr and Cu

  Cr and Cu have unusual configurations because half-filled or completely-filled substance is more stable.
• Energy Levels


  When orbitals fill, the one at the lowest energy level fills first. When full, the 4s orbital moves to a high energy level that the 3d, which is why the 4s is lost first. Electrons occupy sub-shells in order of increasing energy levels.
• Ion Configurations


  When most ions form, they gain a noble gas configuration.
• Ion Configurations in Transition Metals

  When transition metal ions form they lose their 4s electrons first.
• Atomic Number vs Ionisation Energy


  Going down a group, the first ionisation energy decreases because the atoms get larger. The outer electron is further from the nucleus so there is a weaker force of attraction. Also, shielding increases.
• Atomic Number vs Ionisation Energy


  Going across a period the first ionisation energy increases because the nuclear charge increases, because electrons are going into the same shell, so the outer electrons feels a greater force of attraction.
• Atomic Number vs Ionisation Energy


  Anomaly Oxygen’s first ionisation energy is lower than nitrogen‘s because oxygen‘s outer electron is paired and experiences repulsion and is therefore easier to lose (requires less energy to remove).
• Atomic Number vs Ionisation Energy


  Anomaly Boron‘s first ionisation energy is lower than Be because boron‘s outer electron is in P-orbital which is at a higher energy level than Be which is in S-orbital.
• Successive Ionisation Energies of Sodium

  Sodium’s first electrons require little energy to remove because it’s a long way from the nucleus and feels a weaker force of attraction. Sodium’s second to ninth electrons require roughly the same amount of energy to remove because they are in the same shell. The value increases slightly because the ion gets smaller due to a higher force of attraction from the nucleus. Sodium’s tenth and eleventh electrons requires most energy to remove because they are closest to the nucleus (at the lowest energy level).
• Time of Flight (TOF) 


  Method of finding out the mass of a substance.
• Mass Spectrometer

  Technique to find molar masses of unknown substances.
• Stage 1: Ionisation: Electron Impact

  Used for low Mr compounds. High energy electrons are fired at the substance from an electron gun. This knocks off 1 electron from each atom (molecules) to form at 1+ ion.
• Stage 1: Ionisation: Electron Spray Ionisation

  Used for high Mr compounds (eg proteins). Sample is dissolved in a volatile solvent (eg methanol, water) and injected through a fine hypodermic needle as a fine spray into a vacuum in the ionisation chamber. A very high voltage is applied to the end of the needle where the spray emerges (the needle is positively charged). The particles gain a proton and become ions and the solvent evaporates leaving 1+ ions.
• Stage 2: Accelerations of Ions

  The ions are accelerated using an electric field (vibrating them) so that all the ions have the same kinetic energy.
• Stage 3: Separation of Charged Ions

  The 1+ ions enter flight tube through a hole in the negatively charged plates, the lighter ions will travel faster and take less time to reach the detector.
• Stage 4: Detection

  The detection is a negatively charged plate where current is produced when the ions hit the plate (gains 1 electron), the more ions that hit the detector the bigger the current. The simple of the current is proportional to the abundance of each isotope (can be determined using mass spectrometry so can identify and element-useful).
• Standard Enthalpy Change of Combustion

  Enthalpy change when 1 mol of a substance has completely reacted in oxygen with all substances in standard states.
• Standard Enthalpy Change of Formation

  Enthalpy change when 1 mol of a compound is formed from its elements in their standard states under standard conditions.
• Standard Conditions

  1. 298K
  2. 1 mol dm^-3
  3. 100kPa
• Equilibrium


  Constant concentration
• Dynamic Equilibrium

  Rate of forward and backward reactions are equal.
• Closed System


  No reactants or products can escape, only what can be exchanged freely.
• Le Chatlier ‘s Principle

  When a system in dynamic equilibrium is subjected to a change, the position of the equilibrium will shift to minimise this change.
• The position of equilibrium is affected by: Temperature

  When temperature increases, a equilibrium will shift in the endothermic direction to absorb the heat energy and minimise the impact of change.
• The position of equilibrium is affected by: Pressure


  When pressure increases, the position of the equilibrium shifts to the side with fewer molecules, in order to minimise the impact of the change.
• The position of the equilibrium is affected by: Concentration

  When concentration increases, there are more reactants available to react, this moves equilibrium to the right.
• The position of equilibrium is NOT affected by: a Catalyst

  A catalyst does not have affect the position of the equilibrium because it only increases rate of the forward and backward reaction equally.
• Kc

  Equilibrium constant
• Kc=1

  Reaction is halfway.
• Kc>1 


  reaction lies to right, more products.
• Kc<1

  Reaction lies to the left, more reactants.
• Kc is affected by temperature.