year ten - chemistry

• ionic bonding example: NaCl (sodium chloride)

  
  

  1. an electron is transferred to the chlorine atom from the sodium atom
  2. they are drawn together due to their opposite charges.
• an ionic bond is a strong electrostatic force between oppositely charged ions
• a positive ion (has lost electrons) is a cation

  a negative ion (has gained electrons) is a anion
• covalent bonds form when two atoms share one or more pairs of electrons
• molecules are groups of non-metal atoms joined by covalent bonds.
• if two pairs of electrons are shared, this is called a double bond, eg$O_2$
• simple molecular substances:

  • contain separate molecules
  • have a relatively small number of atoms
  • have strong covalent bonds within
  • have weak attractions between molecules
  • have low melting and boiling points
• elements in group 1 lose 1 electron, those in group 2 lose 2 and so on.
• when metals exist as elements, their outer electrons become detached and free to move through the metal.
• alloys are made by adding small amounts of other metals to a molten metal. they have different properties to the parent metal.