Chemistry AS Cheat Sheets

• Atoms are the components that make up all elements
• Atoms


  • Made up of three types of subatomic particles: electrons, protons, and neutrons
  • Protons and neutrons make up the nucleus, where most of the mass is concentrated
  • Electrons orbit the nucleus in shells
• Proton


  Positively charged particle
• Electron


  Negatively charged particle
• Neutron


  Neutral particle
• The model of the atom has changed over time as new evidence has become available
• Dalton's atomic model


  • All atoms of one element are identical and are different from the atoms of other elements
  • Atoms are indivisible
• Thomson's atomic model


  • Discovered the electron
  • Proposed a positively charged atom with negative charges (electrons) embedded in it
• Rutherford's atomic model


  • Most of the mass and positive charge is concentrated in a small, dense nucleus
  • Electrons orbit the nucleus
• Bohr's atomic model


  • Electrons orbit the nucleus in specific, quantized energy levels (shells)
  • Electrons can only occupy certain allowed energy levels
• Current atomic model


  • Composed of protons, neutrons, and electrons
  • Protons and neutrons are found in the nucleus, while electrons surround the central nucleus
• Relative isotopic mass


  The ratio of the mass of an isotope to the mass of carbon-12 (12C)
• Mass number


  The total number of protons and neutrons in an atom
• Isotopes


  Atoms of the same element with the same number of protons but different numbers of neutrons
• Electronic configuration


  The arrangement of electrons in an atom's shells and subshells
• Electron shells


  • Can hold a maximum number of electrons given by 2n^2, where n is the shell number
  • Electrons fill the shells starting from the innermost shell (1s) to the outermost shell
• Orbitals


  Regions within a shell where electrons can be found
• Types of orbitals


  • s, p, d, and f orbitals
• Electrons have an intrinsic property called spin, which can be either up or down
• Electrons in the same orbital must have opposite spins
• Ionisation energy


  The energy required to completely remove an electron from an atom to form a positive ion
• Factors affecting ionisation energy

  • Atomic radius (larger radius, lower ionisation energy)
  • Nuclear charge (greater charge, higher ionisation energy)
  • Shielding of outer electrons by inner electrons (greater shielding, lower ionisation energy)
• Mole


  The amount of substance that contains the same number of particles (atoms, molecules, ions) as 12 g of carbon-12
• Molar mass


  The mass of one mole of a substance
• Concentration


  The amount of solute present in a known volume of solution
• Molar gas volume


  The volume occupied by one mole of any gas under standard conditions (24 L/mol)
• Ideal gas equation


  pV = nRT, where p is pressure, V is volume, n is moles, R is the gas constant, and T is temperature
• Empirical formula


  The simplest whole-number ratio of the atoms of each element present in a compound
• Molecular formula


  The actual number and type of atoms in a molecule
• Balanced equation


  An equation where the number of atoms of each element is the same on both the reactant and product sides
• State symbols


  Indicate the physical state of a substance: (s) solid, (l) liquid, (g) gas, (aq) aqueous
• Spectator ions


  Ions that do not take part in a reaction and are found in both the reactants and products
• Stoichiometry


  The quantitative relationships between the amounts of reactants and products in a chemical reaction
• Atom economy


  The percentage of the total mass of reactants that ends up in the desired product
• Percentage yield


  The ratio of the actual amount of product obtained to the theoretical amount, expressed as a percentage
• Collision theory


  • For a reaction to occur, reactant particles must collide with sufficient energy and in the correct orientation
  • Increasing temperature and the use of catalysts can increase the rate of reaction
• Maxwell-Boltzmann distribution


  The distribution of kinetic energies of gas molecules at a constant temperature
• Effect of temperature and catalysts on the Maxwell-Boltzmann distribution

  • Increasing temperature shifts the distribution to higher energies
  • Catalysts lower the activation energy, allowing more molecules to have sufficient energy to react
• Rate of reaction


  The change in the concentration of reactants or products over time
• Chemical equilibrium


  A state where the rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant