C2 2

C2 2.1

• Molecule - two or more atoms joined by covalent bonds (two electrons shared between two atoms).
• The formula of a simple molecular substance tells us how many atoms of each type are in one molecule.
• Covalent bonds in molecules are very difficult to break, breaking them conctitutes a chemical change as different substances are formed.
  • Although the bonds are broken there are weak forces called intermolecular forces.
    • These forces are far weaker  than the three types of bonding (ionic, covalent and metallic)
• Simple molecular substances - millions of seperate but identical molecules.
• When simple molecular substances melt or boil, it is the weak forces between molecules that are overcome (the covalent bonds do not break)
• • for example the molecules in all the different states of water are all H2O molecules.
• Simple molecular substances have low melting and boiling points (because the forces between the molecules are so weak)
• Simple molecular substances do not conduct electricity in any state.

C2 2.2

• Ions - An electrically charged particle where the number of protons differs from electrons.
  • An atom that has lost or gained one or more electrons.
  • Ionic substances are compounds made from both metals and non-metals.
  • Examples include - sodium chloride, copper sulfate and calcium carbonate.
• Ionic compounds are solids at room temperature.
• The ions are packed together in a regular structure called a giant lattice.
• Each ion is surrounded by ions of the opposite charge so they are held together by strong electrostatic atraction - ionic bonding.
• The formula of an ionic compound tells us the ratio of ions in the compound.
  • example - NaCl - 1 Na+ for every Cl-.
• Ionic compounds have high melting and boiling points.
• All ionic compounds are solids at room temperature.
• When the ion is melted, the ions can move around and so conduct electricity.
• When ionic compounds are dissolved in water they conduct electricity.

C2 2.3

• Atoms…