Physics

• History of the Atomic Model:

  • Democritus (400 BC): first person to hypothesize about matter consisting of smaller indivisible particles called "atomas" (Greek for uncuttable)
  • John Dalton (1803): introduced the first modern-day atomic theory known as the Billiard Ball model
  • Joseph Thomson (1897): discovered the electron and proposed the Plum Pudding model
  • Ernest Rutherford (1909-1911): developed the Nuclear (or Planetary) model, discovered the nucleus and proton through the Gold foil Experiment
  • Niels Bohr (1922): introduced the Energy Level Model where electrons occur in fixed orbitals, explaining the line spectrum of hydrogen
  • Schrodinge (1930 & onwards): developed the Quantum Mechanical Model (or Electron Cloud Model) based on wave equations and modern quantum theory
  • James Chadwick (1932): revised the Nuclear Model and discovered the neutron
• To find the moles of water of crystallisation in a compound, such as hydrated sodium carbonate, use the formula M(Na2CO3.nH2O) = 286.14 g/mol
• In the case of an aluminium chloride hydrate (AlCl3.nH2O), if the compound weighs 2.455 g initially and 1.375 g after heating, the moles of water of crystallisation can be found by calculating the moles of AlCl3 and the difference in weight before and after heating
• The molar mass of a compound is the mass of one mole of the compound and is expressed in g/mol
• The molar volume of gases at standard temperature and pressure (STP) is 22.4 dm³/mol, and the formula relating moles, volume, and molar volume is n = V/VM
• For calculations involving elementary particles, the formula relating moles and number of particles is N = n x NA, where NA is Avogadro's constant (6.02 x 10^23 particles/mol)
• The formula relating moles, mass, and molar mass is n = m/M, where n is the number of moles, m is the mass of the sample in grams, and M is the molar mass in g/mol
• The mole is the SI unit for the amount of substance, defined as the number of particles it contains, with 1 mole containing Avogadro's number of particles (6.02 x 10^23)
• Avogadro's constant states that the number of atoms contained in exactly 12 g of ¹²C is 6.02 x 10²³
• Molar mass is the mass of one mole of any substance, expressed in g/mol, and has the same value as the relative atomic or molecular mass
• Examples of molar mass:

  • Sodium (Na): 23 g/mol, one mole weighs 23g
  • Iron (Fe): 56 g/mol, one mole weighs 56g
• Percentage composition of each element in a compound can be calculated by determining the relative molecular mass and the relative atomic mass of the element
• Water of crystallisation refers to water molecules trapped within the crystal structure of salts, and each hydrate has a specific number of water molecules associated with it
• Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons
• Atomic mass is the actual mass of an average atom of an element, including all isotopes, measured in atomic mass units (u)
• Atomic number is the number of protons in the nucleus of an atom, while mass number is the number of nucleons (protons + neutrons) in a nucleus
• Relationship between the number of electrons and an element's atomic number: Number of electrons = atomic number in a neutral atom
• Cations:

  • Name: Ammonium (Hydronium)
  • Formula: NH₄⁺ (H₃O⁺)
• Anions:

  • Names: Chlorate, Ethanoate (acetate), Hydroxide, Nitrite, Nitrate, Permanganate, Carbonate, Hydrogen carbonate (bicarbonate), Sulphite, Sulphate, bisulphate, Hydrogen sulphate, Thiosulphate, Phosphate, Dichromate
  • Formulas: ClO₃, CH₃COO⁻, OH⁻, NO₂, NO₃, MnO₄, CO₃²⁻, HCO₃⁻, SO₃²⁻, SO₂²⁻, HSO₄⁻, S₂O₃²⁻, PO₄³⁻, Cr₂O₇²⁻