Chemistry Summary

• Features of the Atomic Structure

  • Atoms are the components that make up all elements
  • Atoms are made up of three types of sub-atomic particles – protons, neutrons, and electrons
  • Protons and neutrons make up the nucleus, where most of the mass is concentrated. Electrons orbit the nucleus in shells
• Mass Number & Isotopes

  • Mass number, A, is the total number of protons and neutrons in the nucleus
  • Atomic number, Z, is the number of protons. The number of positively charged protons is equal to the number of negatively charged electrons in an atom, making the atom neutrally charged
  • Mass number = number of protons + number of neutrons
  • Atomic number = number of protons = number of electrons
  • Ions are formed by atoms losing or gaining electrons. A charge of x- means that the number of electrons in the ion is the atomic number + x. A charge of x+ means that the number of electrons in the ion is the atomic number - x
  • Isotopes are atoms with the same number of protons and different numbers of neutrons. Therefore, they have different mass numbers but the same atomic number
  • Isotopes of the same element have the same electronic configuration so react in the same way in chemical reactions but have slightly different physical properties
• Relative Masses


  • Relative isotopic mass is the mass of an atom of an isotope compared with 1/12th of the mass of an atom of carbon-12. For an isotope, the relative isotopic mass = its mass number
  • Relative atomic mass is the ratio of the average mass of an atom of an element to 1/12th of the mass of an atom of carbon-12
  • Relative molecular mass is the ratio of the average mass of a molecule of an element or compound to 1/12th of the mass of an atom of carbon-12
  • Relative formula mass is similar to relative molecular mass but applies to ionic compounds
• Mass Spectrometry is a fo
• Relative molecular mass


  Ratio of the average mass of a molecule of an element or compound to 1/12th of the mass of an atom of carbon-12
• Relative formula mass


  Similar to relative molecular mass but applies to ionic compounds
• Mass Spectrometry


  1. Form of molecular chemical analysis that allows the masses of individual molecules or isotopes to be determined

  2. Can provide structural information, identify an unknown compound, or determine the relative abundance of each isotope of an element

  3. Mass spectrum gives information about the relative abundance of isotopes on the y-axis and about the relative isotopic mass on the x-axis

  4. Can be used to determine the relative atomic mass (Ar)

  5. Mass spectrum for a molecular sample shows the relative molecular mass on the x-axis
• Electronic Configuration


  1. Electrons orbit the central nucleus in shells, each shell can hold 2n^2 electrons where n is the principal quantum number

  2. Electron shells are made up of atomic orbitals, which are regions in space where electrons may be found

  3. Each shell is composed of one or more orbitals and each orbital can hold one pair of electrons

  4. Four main types of orbitals: s-, p-, d-, and f-

  5. Different orbitals possible in each subshell: 1 s-orbital, 3 p-orbitals, 5 d-orbitals, and 7 p-orbitals

  6. Shells and sub-shells are filled with electrons according to a set of rules

  7. Electron configuration is written with n representing principal quantum number, X is the type of orbital, and y is the number of electrons in the orbitals of the subshell

  8. Electronic configurations of ions can be determined by using the same building up principle

  9. Electrons have an intrinsic property (spin), for two electrons in the same orbital, the spin must be opposite to minimize the repulsion

  10. No more than two electrons can fill an atomic orbital
• An ion is an atom or molecule with a net charge formed through the gain or loss of electrons
• A cation is formed from the loss of electrons
• An anion is formed from the gain of electrons
• Empirical formula is the simplest whole-number ratio of atoms of each element present in a compound
• Empirical formula can be calculated from the composition by mass or percentage by mass
• Calculating empirical formula of a compound

  Subtracting masses, calculating moles, dividing by smallest number of moles to get whole number ratio, determining empirical formula
• Molecular formula


  Gives the number and type of atoms of each element in a molecule, made up of a whole number of empirical units
• Determining molecular formula


  Calculating relative molecular mass, dividing by relative molecular mass of empirical formula, determining molecular formula
• The mole is the unit used to quantify the amount of a substance
• A mole is the amount of substance that contains the same number of atoms or particles as 12 g of carbon-12
• The number of particles in 12g of 12C is the Avogadro constant of 6.022 x 10^23 mol-1
• Concentration of a solution


  Amount of solute present in a known volume of solution
• Gas volume under standard conditions

  One mole of any gas occupies the same volume, molar gas volume is 24 dm^3 mol^-1
• Calculating number of moles of gas


  Using volume and molar gas volume under standard conditions
• Ideal gas assumptions
• Ideal gas equation


  pV = nRT
• In a chemical reaction, no atoms are created or destroyed
• In a balanced equation, there is the same number of atoms of each element in both the reactants and products
• State symbols


  • Solid (s)
  • Liquid (l)
  • Gaseous (g)
  • Aqueous (aq) - dissolved in water
• Writing ionic equations


  Include only reacting ions and the products they form
• Writing net ionic equations

  Show only ions directly involved in the reaction, removing spectator ions
• Atom economy is a theoretical measure of the proportion of atoms from the reactants that form the desired product
• Advantages of maximising atom economy

  • More sustainable (uses fewer raw materials)
  • Minimises chemical waste
  • Maximises efficiency
  • Less money is spent on separation processes
• The limiting reagent dictates the theoretical yield and the amount of product actually formed
• Percentage yield is a measure of the efficiency of a reaction
• Limiting reagent


  The reagent not in excess. It dictates the theoretical yield and the amount of product actually formed
• Percentage yield


  A measure of the percentage of reactants that have been converted into the desired product. It gives a measure of the efficiency of a reaction route
• Percentage yield is reduced by

  The formation of unwanted by-products, any reactant that remains unreacted, or product that cannot be extracted from the reaction vessel
• Common acids


  • Hydrochloric acid, HCl
  • Sulphuric acid, H2SO4
  • Nitric acid, HNO3
• Acids dissociate in water

  HA (aq) ⇌ A– (aq) + H+ (aq)
• Strength of an acid

  Describes how much of it dissociates when it dissolves
• Strong acid


  • It dissociates almost completely in water or aqueous solution. HA (aq) ⇌ A– (aq) + H+ (aq)