AP2-CHEM

• What is an atom?

  All substances are made of atoms. An atom is the smallest part of an element that can exist.
• How are compounds formed?

  formed from elements by chemical reactions. Chemical reactions always involve the formation of one or more new substances, and often involve a detectable energy change.
• Compounds contain two or more elements chemically combined in fixed proportions and can be represented by formulae using the symbols of the atoms from which they were formed. Compounds can only be separated into elements by chemical reactions.
• What does a mixture consist of?

  two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged.
• How can mixtures be seperated?

  physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography. These physical processes do not involve chemical reactions and no new substances are made.
• Elements that react to form positive ions are metals. Elements that do not form positive ions are non-metals. The majority of elements are metals. Metals are found to the left and towards the bottom of the periodic table. Non-metals are found towards the right and top of the periodic table.
• What is Group 0 called?

  Noble gases
• Are Group 0 reactive?

  No
• Group 0 of the periodic table are called the noble gases. They are unreactive and do not easily form molecules because their atoms have stable arrangements of electrons. The noble gases have eight electrons in their outer shell, except for helium, which has only two electrons. The boiling points of the noble gases increase with increasing relative atomic mass (going down the group).
• What is Group 1 called?

  Alkaline Metals
• Group 1 of the periodic table

  Alkali metals
• Alkali metals


  • Have a single electron in their outer shell
• Reactions of the first three alkali metals

  1. With oxygen

  2. With chlorine

  3. With water
• Going down Group 1

  The reactivity of the elements increases
• Group 7


  The halogens
• Halogens


  • Have seven electrons in their outer shell
  • Are non-metals
  • Consist of molecules made of pairs of atoms
• Further down Group 7 an element is

  The higher its relative molecular mass, melting point and boiling point
• Going down Group 7

  The reactivity of the elements decreases
• The earth's atmosphere is composed of about 80% nitrogen, 20% oxygen, and less than 1% of other gases like carbon dioxide, water vapor, and noble gases
• How the earth's atmosphere evolved


  1. Volcanic activity produced CO2, water vapor, nitrogen, methane, ammonia

  2. Water vapor condensed into oceans, allowing CO2 to dissolve

  3. Algae and plants evolved, using CO2 for photosynthesis and producing O2

  4. Organic matter from dead algae/plants became buried and formed sedimentary rocks, oil, and gas
• The early atmosphere was mostly CO2, similar to Mars and Venus
• Photosynthesis takes in CO2 and produces O2
• As algae and plants photosynthesized


  Atmospheric CO2 levels declined and O2 levels increased
• More complex life like animals could evolve with the increased O2 levels
• Types of sedimentary deposits formed from buried organic matter


  • Crude oil and natural gas (from dead plankton)
  • Coal (from dead plant material)
  • Limestone (from calcium carbonate in marine organism shells/skeletons)
• The exact substance formed depends on the type of organism being buried and the conditions involved
• This process of atmosphere evolution is a theory, supported by evidence, but not a certainty due to the long timescale involved
• Crude oil


  A fossil fuel that we get from deep under the ground, a mixture of lots of different compounds
• Crude oil


  • Nearly all of the compounds in crude oil are hydrocarbons which contain only hydrogen and carbon
  • The most common type of hydrocarbons are alkanes
• Formation of crude oil


  Remains of dead plants and animals, particularly plankton, buried in mud and turned into crude oil over millions of years by high pressures and temperatures under the ground
• Crude oil is a finite resource, if we continue to extract and use it at the current rate we will run out of it one day
• Fractional distillation


  A process used to separate the different hydrocarbons in crude oil by making use of their different boiling points
• Fractional distillation


  1. Feed the oil into a chamber and heat it until most of it has turned into a gas

  2. Pass the gaseous mixture into a fractionating column which is hot at the bottom and gets cooler towards the top

  3. The hydrocarbons condense into liquids at different heights in the column based on their boiling points
• Fractions obtained from fractional distillation


  • Bitumen (used to surface roads)
  • Heavy fuel oil (can be separated further)
  • Diesel and petrol (used in cars and other road vehicles)
  • Kerosene (used in jet engines)
  • LPG (contains mainly propane and butane)
• Fractions from fractional distillation


  • The shorter chain hydrocarbons are the most flammable and make the best fuels
  • The longer chain hydrocarbons are often poor fuels and may need to be broken down further
• Petrochemicals


  Substances obtained from crude oil that can be used as feedstock (raw materials) for the petrochemical industry to make things like solvents, lubricants, polymers and detergents
• Potable water


  Water that's safe to drink
• Getting potable water


  1. Treating fresh water sources

  2. Desalinating seawater
• Pure water


  Contains only H2O molecules
• Portable water


  Often contains other dissolved substances, making it impure