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• ions are made when electrons are transferred
• ions are charged particles that can be single atoms or groups of atoms
• when atoms lose or gain electrons to form ions, they are trying to stabilize, and gain a full outer shell
• when metals form ions, they lose electrons from their outer shell to form positive ions
• hen non-metals form ions, they gain electrons into their outer shell to form negative ions
• the number of electrons lost or gained is the same as the charge on he ion. If 2 electrons are lost, the charge is 2+
• group 1&2 and 6&7 are the most likely to form ions
• groups 1 and 2 are metals that lose electrons to form positive ions (cations)
• group 6 and 7 elements are non-metals that gain electrons to form negative ions (anions)
• group 1 elements form 1+ ions

  group 2 elements form 2+ ions

  group 6 elements form 2- ions

  group 7 elements form 1- ions
• ionic bonding is when a metal and a non-metal react together. The metal atom loses electrons and is a positively charged ion
• in ionic bonding, the non-meal gains electrons and is negatively charged
• in ionic bonding, the oppositely charged ions are strongly attracted to each other by electrostatic forces. this is called an ionic bond
• dot and cross diagrams show the arrangement of electrons in an atom or ion. They help to represent electron exchange from atoms
• dot and cross diagrams

  
• ionic compounds have a structure called a giant ionic lattice
• in ionic compounds, the ions form a closely packed regular lattice and there are very strong electrostatic forces of attraction between oppositely charged ions in all directions of the lattice
• ionic compounds all have similar properties:

  • high melting and boiling points
  • when solid they cannot conduct electricity
  • when melted, they conduct electricity
• when ionic compounds are solid, the electrons are held in place, so they cannot conduct electricity, but when melted they are then free to move, so can conduct
• covalent bonds are between 2 non-metals, that share a pair of electrons to make covalent bonds
• covalent bonds - the positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong
• each single covalent bond provided one extra shared electron for each atom
• each atom involved generally has enough covalent bonds to fill up its outer shell
• Covalent bonds are present in compounds of non-metals or non-metal elements
• molecular formula diagrams

  
• Covalent bonds: hydrogen

  hydrogen atoms have just one electron, so they only need one more to complete the outer shell, so they often form single covalent bonds
• Covalent bonds: Chlorine

  each chlorine atom needs just one more electron to fill its outer shell. So 2 chlorine atoms can share one pair of electrons and form a single covalent bond
• Covalent bonds: oxygen

  each oxygen need 2 more electron to complete its outer shell. So in oxygen gas, 2 oxygen atoms share 2 pairs of electrons making a double covalent bond
• Covalent bonds: nitrogen

  nitrogen atoms need 3 more electrons. So 2 nitrogen atoms share 3 pairs of electrons to fill their outer shells, this creates a triple bond
• Covalent bonds: Methane

  Carbon has 4 outer electrons, which is half a full shell.

  It can form 4 covalent bonds with hydrogen atoms to fill its outer shell
• Covalent bonds: water

  in water molecules, the oxygen shares a pair of electrons with 2 hydrogen atoms to form 2 single covalent bonds
• properties of simple molecular substances:

  • forces of attraction between molecules are very weak
  • to melt or boil, you only need to break weak intermolecular forces and not the covalent bonds
  • most are gases or liquids at room temperature
  • as molecules get bigger, strength of intermolecular forces increases so more energy is required
  • do not conduct electricity
• a polymer is a long chain of repeating units - lots of small units linked to form a long molecule
• all the atoms in a polymer are joined by strong covalent bonds
• the inermolecular forces between polymer molecules are larger than between simple covalent molecules, so more energy is required to break them
• most polymers are solid at room temperature
• intermolecular forces of polymers are still weaker than ionic or covalent bonds so they generally have lower boiling points
• Giant covalent structure - Diamond

  each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure

  
• giant covalent structure - graphite

  each carbon atom has formed 3 covalent bonds to create layers of hexagons - each carbon atom also has one delocalized electron

  
• giant covalent structures - silicon dioxide