chemistry st2 (year 9)

• The atomic mass is the number of protons and neutrons added
• The atomic number is the number of protons in the
• How to work out the number of neutrons

  Subtract the number of protons and electrons from the atomic mass
• Atoms have no overall electrical charge because they are neutral (protons = electrons)
• Elements in the same group

  • Have the same number of outer electrons e.g. noble gases (group)
• Element

  Substance made of one type of atom
• Compound

  Contains one or more type of atom chemically bonded together
• Mixture

  Molecules of element or compounds mixed together without chemical bonds
• Electron


  Particle with charge -1
• Proton


  Particle with charge +1
• Neutron


  Particle with charge 0
• Atoms can only have 2 electrons on the innermost shell and only 8 electrons on the outermost shell
• Hydrocarbon

  Compound made of just hydrogen and carbon atoms
• Saturated atoms

  • Held together by single covalent bonds
• Alkane


  Saturated hydrocarbon (only single bonds)
• Alkene


  Not saturated, has double bonds
• Alkane formula


  CnH2n+2
• Alkene formula


  CnH2n
• Crude oil

  Mixture of many hydrocarbon compounds
• Separation of crude oil

  Evaporating (liquid -> vapour) the oil to condense (vapour -> liquid) at different temperatures
• Fractional distillation


  • Separates crude oil into fractions containing molecules with similar number of carbon atoms
• Short chain hydrocarbons have lower boiling points, long chain hydrocarbons have higher boiling points
• Hydrocarbon separation

  Oil is heated until evaporation

  2. Gases rise

  3. Vapours travel up the tower

  4. They condense on trays when they reach the right temperature

  5. Outlet trays collect the liquid fraction after condensation
• Fractioning column is a tall tower which is hotter at the bottom and cooler at the top
• Lighter hydrocarbons rise to the top, heavier hydrocarbons rest nearer the bottom
• Most fuels contain carbon, hydrogen (and sulfur)
• Combustion

  The process of breaking down by burning, involves reaction of elements in burning substances (with oxygen) producing oxides
• Combustion of hydrocarbon fuels releases energy as the hydrogen and carbon are oxidised
• Oxides of each element in the burning substance are produced
• Combustion can release carbon dioxide, water, carbon monoxide, sulfur dioxide, oxides of nitrogen, and particulates
• Soot and unburnt fuels are caused by limited air or incomplete combustion
• Cracking

  Heating hydrocarbons to vaporise them, then passing the vapours over a hot catalyst to produce smaller and more useful molecules
• Cracking involves a thermal decomposition reaction
• no atoms are lost or made during a chemical reaction. symbol equations must always be balanced
• to calculate Rf value, you divide the distance moved by a substance by the distance moved by the solvent
• when heating a liquid-liquid mixture, the component with the lower boiling point evaporates first
• unreactive metals are found in their native state and are mostly found as compounds
• ores

  • mined and may be concentrated before extracted and purified
  • metals that are less reactive than carbon can be extracted from their oxides by reduction with carbon
• smelting involves heating the copper ore to produce crude copper which may be purified by electrolysis
• phytomining is a way of extracting copper by using plants to absorb metal compounds which are burned to produce ash containing the metal compounds