Chemistry

• The periodic table didn't start out looking like it does now
• Early periodic table development

  • Developed by multiple people
  • Grouped elements into groups of 8 (octaves)
• Newlands' octave had issues - no gaps, mixed metals and nonmetals, included non-elements
• Mendeleev's periodic table

  • Had gaps, predicted properties of undiscovered elements
  • Arranged elements into groups
• Modern periodic table

  • Arranged by atomic number, which also arranges by electron structure
  • Has some elements in unexpected positions due to atomic mass
• Groups on the periodic table

  • Noble gases
  • Halogens
  • Alkali metals
• Periods

  Horizontal rows, indicate number of electron shells
• Groups

  Vertical columns, indicate number of electrons in outer shell
• Mass number

  Number of protons and neutrons
• Atomic number


  Number of protons
• Subatomic particles

  • Protons (mass 1)
  • Neutrons (mass 1)
  • Electrons (mass 0)
• Protons have +1 charge, neutrons are neutral, electrons have -1 charge
• Group 1 (alkali metals)


  • Highly reactive, produce salt and hydrogen gas when reacting with water
  • Reactivity increases down the group
• Shielding

  Electron shells getting in the way of the positive nucleus pulling in electrons, making elements less reactive
• Group 7 (halogens)

  • Most reactive at the top of the group
  • Generally found as diatomic molecules
• Balancing chemical equations

  1. Adjust coefficients to make number of atoms equal on both sides

  2. Aim for even numbers on both sides
• State symbols indicate if a product is a gas or solid
• State symbols

  • aq = aqueous (dissolved in water)
  • ppt = precipitate (solid formed)
  • g = gas
• Ionic bonding

  • Occurs between metals and nonmetals
  • Metals form positive ions, nonmetals form negative ions
  • Resulting ionic lattice has high melting/boiling points and does not conduct electricity (except when molten/dissolved)
• The atmosphere is mainly nitrogen (78%) and oxygen (21%), with small amounts of other gases like argon and carbon dioxide
• Covalent bonding

  • Occurs between nonmetals
  • Involves sharing of electrons
  • Results in low melting/boiling points and no electrical conductivity (unless in covalent networks)
• Covalent network structures

  • Diamond and silicon dioxide
  • Have high melting/boiling points and do not conduct electricity
• Methane formation

  1. Methane (CH4) formation

  2. Carbon has 4 bonds

  3. Each hydrogen forms 1 water (H2O)

  4. Oxygen in the middle, 2 hydrogens either side
• Ammonia formation

  1. Ammonia (NH3) formation

  2. Nitrogen has 3 bonds

  3. 3 hydrogens
• Simple covalent molecules

  • Low melting points
  • Low boiling points
  • Do not conduct electricity
  • Generally gas or liquid at room temperature
• Covalent structures

  • Diamond
  • Silicon dioxide
• Diamond

  • Made of carbon
  • 4 bonds
  • Hard
  • Strong
  • High melting and boiling points
  • Do not conduct electricity
• Graphite

  • Made of carbon
  • 3 bonds
  • Soft
  • Layers can slide
  • Free electrons between layers, so can conduct electricity
• Making copper sulfate

  1. Add copper oxide to hot sulfuric acid

  2. Stir until black powder won't dissolve

  3. Filter to get blue solution

  4. Evaporate water to get copper sulfate crystals
• Testing for negative ions

  1. Add dilute nitric acid - should fizz for carbonate

  2. Add silver nitrate - white for chloride, cream for bromide, yellow for iodide

  3. Add barium chloride and hydrochloric acid - white precipitate for sulfate
• Relative formula mass

  Mass of a molecule calculated from the masses of its atoms
• Calculating percentage composition

  1. Take mass of element

  2. Divide by total formula mass

  3. Multiply by 100
• Calculating reacting masses

  1. Find masses of reactants and products

  2. Set up ratio

  3. Multiply ratio by known mass to find unknown mass
• Electrolysis

  1. Negative ions go to positive electrode

  2. Positive ions go to negative electrode

  3. Oxidation is loss of electrons, reduction is gain of electrons
• Electrolysis of aluminium oxide

  1. Negative oxygen ions go to positive carbon electrode, forming CO2

  2. Positive aluminium ions go to negative electrode, forming aluminium metal
• Metallic bonding

  • Layers of positive ions
  • Free moving electrons between layers
  • Allows sliding and conduction
• Alloys

  • Disrupt the layers, making the metal harder and stronger
• Shape memory alloys

  • Can remember and return to original shape after deformation
• pH scale

  • 1 is very acidic, 14 is very alkaline
  • Acidity from hydrogen ions, alkalinity from hydroxide ions
  • Neutral is pH 7 (H+ + OH- -> H2O)
• Endothermic and exothermic

  Endothermic reactions take in energy, exothermic reactions give out energy