Chem Paper 1

• Atom


  Tiny particle of matter that is the building block of all matter
• Atoms


  • Made of subatomic particles called protons, neutrons, and electrons
  • Protons and neutrons are located in the nucleus
  • Electrons move fast around the nucleus in orbital paths called shells
  • Mass of the atom is contained within the nucleus
• The atom is the smallest part of an element that exists even though it can be divided into smaller particles
• Element


  A substance made of atoms that all contain the same number of protons and cannot be split into anything simpler
• There is a limited number of elements, and all elements are found on the Periodic Table
• Chemical symbol


  A unique symbol representing each element on the Periodic Table
• The first letter of a chemical symbol is always uppercase, the second letter is lowercase
• Some elements exist as diatomic molecules in nature: H2, N2, O2, F2, Cl2, Br2 and I2
• The atomic number and mass number are also shown on the Periodic Table
• You need to be able to use the names and symbols for the first 20 elements in the Periodic Table, as well as group 1, group 7 and any other elements specified
• Compound


  A pure substance made up of two or more elements chemically combined, and which cannot be separated by physical means
• The properties of compounds are usually quite different from the elements that form them
• There is an unlimited number of compounds, and the chemical formula is what tells you the ratio of atoms in a compound
• Diagrams or models can also be used to represent the chemical formula
• A common error is to say elements are pure while compounds are impure. Pure substances contain only one element or compound and are not mixed with anything else e.g., water that contains H2O molecules only is pure whereas if salt is added it then becomes impure
• Ionic compounds


  Contain metal and non-metal elements joined together as particles called ions
• Covalent compounds


  Contain only non-metals
• Naming conventions for compounds

  • Metal and non-metal (metal symbol first, non-metal ending in '-ide' unless oxygen present then ending in '-ate')
  • Non-metal only (use prefixes like mono, di, tri to show number of each element)
• Covalent compound names


  • CO2 - carbon dioxide
  • NO - nitrogen monoxide
  • SiCl4 - silicon tetrachloride
• Common names of covalent compounds

  • H2SO4 - sulfuric acid
  • NH3 - ammonia
  • CH4 - methane
  • HCl - hydrochloric acid (or hydrogen chloride if gas)
  • C6H12O6 - glucose
  • C2H5OH - ethanol
  • HNO3 - nitric acid
• Word Equations


  Show the reactants and products of a chemical reaction using their full chemical names
• Reactants


  Substances on the left-hand side of the arrow, the chemical ingredients of the reaction
• Products


  New substances on the right-hand side of the arrow, formed from the reaction
• Arrow


  Implies the conversion of reactants into products
• Reaction conditions


  Can be written above the arrow
• Catalyst


  A substance added to make a reaction go faster, can be written above the arrow
• Half equations


  Used to show what happens to the electrons in reactions where atoms, molecules or ions are gaining or losing electrons
• Example reaction


  • Sodium hydroxide + hydrochloric acid ⟶ sodium chloride + water
• Ionic equations


  Used to indicate what happens to ions during reactions, help to simplify complicated processes where many substances are present, but only certain ions are actually reacting with each other
• Symbol Equations


  Use the formulae of the reactants and products to show what happens in a chemical reaction
• Ions which are present but do not take part in reactions are called spectator ions
• Examples of half equations

  • Pb2+ + 2e- → Pb

  2Br- → Br2 + 2e-
• Symbol equations must be balanced to give the correct ratio of reactants and products
• Half equations and ionic equations are specific types of equations for showing some of the fine details going on in chemical reactions
• Nothing is created or destroyed in a chemical reaction, the same atoms are always present before and after
• Law of Conservation of Mass


  The total mass of reactants is always equal to the total mass of products
• Balancing Equations


  1. Write formulae and balanced chemical equations

  2. Not change any of the formulae

  3. Put the numbers used to balance the equation in front of the formulae

  4. Balance firstly the carbon, then the hydrogen and finally the oxygen in combustion reactions of organic compounds
• Worked example


  • 2Mg (s) + O2 (g) → 2MgO (s)
• Chemical equations do not contain an equals sign between the left and right-hand sides but are written with an arrow instead
• Mixtures


  Can contain elements and/or compounds

  Each constituent of the mixture retains its chemical properties

  The parts of a mixture are not chemically bonded together and so they can be separated by physical means

  The choice of the method of separation depends on the nature of the substances being separated

  All methods rely on there being a difference in a physical property such as the boiling point or solubility, between the substances being separated