Chemistry

• The temperature at which a pure substance turns into a liquid is called the melting point.
• A few solids e.g carbon dioxide (carbon dioxide) do not melt when they are heated at normal pressure. instead they turn directly into gas , This is called sublimation
• Sublimation:  conversion of a substance from the solid to the gaseous state without it becoming liquid
• Separating a liquid from a solution is usually carried out by distillation
• Chromatography

  • Base line must be drawn in pencil, this is to avoid the ink spoiling the experiment since ink dissolves in the solvent
  • The lid is required for saturation
  • Base line must be above solvent line
• Atom: The smallest part of an element that can take part in chemical change

  Element: A substance containing only one type of atom eg carbon (C)

  Molecule: A particle made up of two or more atoms held together by a covalent bond eg Oxygen (O2)

  Compound: A substance containing two or more atoms chemically combined

  Ion: An atom or group of atoms which is negatively or positively charged
• Structure of an atom

  • In the center of an atom is a tiny nucleus
  • The nucleus is made up of protons & neutrons
  • Outside the nucleus are electrons
  • The electrons will be in the electron shell/ orbit
• S.A.P Relative Mass Relative Charge Location

  • Proton 1 +1 nucleus
  • Neutron 1 0 nucleus
  • Electron 1/1840 -1 electron shell / orbit
• No. of protons = the bottom number

  No. of electrons = the bottom number

  Mass no. = the top number

  No. of neutrons = mass number - proton number ( top no. - bottom no.)
• Ionic compounds

  • Formed by the transferring of electrons from metals to non-metals
  • Group 1 , 2 and 3 are called metals and group 4 , 5 , 6 and 7 are non metals
  • Group 8 is a non-metal but it is unreactive
• Group 1: Group 7 (VII):

  Li ( lithium) F ( Florine)

  Na ( Sodium) Cl ( Chlorine)

  K ( Potassium) Br ( Bromine)

  I ( Iodine)
• Ionic or Covalent Bond?

  • Ionic bonds have high melting/boiling points because they have strong forces of attraction between the ions
  • Ionic compounds are soluble in water but insoluble in organic compounds
  • Ionic compounds conduct electricity when molten
  • Covalent bonds have low melting/ boiling points because they have weak intermolecular forces
  • Covalent compounds are insoluble in water
  • Covalent compounds do not conduct electricity
• Electrolysis is the breaking down of an ionic compound when molten or in an aqueous solution through the passage of electricity
• Anode = positive ( left ) - a non- metal is formed

  Cathode = negative ( right ) - a metal is formed
• Reactions that GIVE OUT heat energy are called EXOTHERMIC reactions

  Reactions that TAKE IN heat energy are called ENDOTHERMIC reactions
• Factors affecting the rate of reactions are:

  Temperature

  Surface area

  Catalyst

  Concentration
• Oxidation: Addition of oxygen in reactions

  Reduction: Removal of oxygen in chemical reactions

  Redox: reduction and oxidation take place at the same time
• pH- 0 - 6 = acidic

  pH- 8 - 14 = alkaline

  pH 7 is neutral
• Acids:

  • Turns blue litmus paper red
  • pH below 7
  • Taste sour
  • Corrosive
  • Conduct electricity
  • React with metals to from hydrogen gas

  Base:

  • pH above 7
  • Taste bitter
  • Conduct electricity
  • Turns red litmus paper blue