Bonding, structure and properties of matter

• Ions are charged particles.
• Metals lose electrons to form positive ions, and non-metals gain electrons to form negative ions.

  The number of electrons gained or lost is the same as the charge of the ion, eg. if two electrons are lost, the charge is 2+.
• The elements that most readily form ions are in groups 1, 2, 6 and 7.
• Positive ions are known as cations.

  Negative ions are known as anions.
• Ionic bonding is where a metal and a non-metal react together.

  The metal atom loses electrons and the non-metal gains these electrons. This means they have opposite charges, and are strongly attracted to each other by electrostatic forces.
• In ionic compounds, there are no free electrons so they cannot conduct electricity when solid or liquid. However, when melted or dissolved, the ions can move freely and allow current to flow through the solution.
• Dot and cross diagrams are useful for showing how ionic compounds are formed, but don't show the structure of the compound, size of the ions or how they're arranged.
• Ionic compounds have a structure called a giant ionic lattice.

  They form a closely packed regular lattice arrangement and there are very strong forces of attraction in all directions in the lattice.
• Ionic compounds all have high melting and boiling points due to the many very strong bonds between the ions.
• Covalent bonding happens between two non-metals and involves a shared pair of electrons.

  The positively charged nuclei of the bonded atoms are attracted to the the shared pair of electrons by electrostatic forces, making covalent bonds very strong.
• Simple molecular substances are molecules made of a few atoms joined together by covalent bonds. Some examples are hydrogen, chlorine, oxygen, nitrogen, methane, water and hydrogen chloride.
• Simple molecular substances have very weak forces of attraction between each molecule, meaning the melting and boiling points are very low.
• Most molecular substances are gases or liquids at room temperature.
• Molecular compounds don't conduct electricity because they are not charged.
• A polymer is a long molecule made of repeating units called monomers.
• All the atoms in a polymer are joined by strong covalent bonds.
• Most polymers are solid at room temperature
• In giant covalent structures, all the atoms are bonded to each other by strong covalent bonds. They have very high melting and boiling points.
• Giant covalent structures don't conduct electricity.
• In diamond, each carbon atom forms four covalent bonds in a rigid giant covalent structure.
• In graphite, each carbon atom forms three covalent bonds to create layers of hexagonal rings. Each carbon atom has one delocalised electron.
• Diamond, graphite, graphene and fullerenes are all allotropes of carbon.
• Fullerenes are molecules of carbon shaped like closed tubes or hollow balls.
• Fullerenes can be used to 'cage' another molecule.
• Fullerenes can form nanotubes, which have a high tensile strength and conduct electricity and heat.
• Some uses for fullerenes include catalysts, lubricants, and drug delivery systems.
• In metallic bonding, the electrons in the outer shell of the metal atoms are free to move around the structure (delocalised).
• In metallic bonding, there are strong forces of electrostatic attraction between the positive metal ions and the negative electrons.
• Most compounds with metallic bonds have high melting and boiling points.
• The layers of atoms in a metal can slide over each other, making metals malleable.
• Pure metals are often too soft to be used in everyday products, so they're mixed with other metals in alloys.
• Alloys are stronger than pure metals because the atoms of different sizes distort the layers in the metal, making it harder for them to slide over each other.
• Solids have a fixed shape and volume. The particles vibrate in fixed positions.
• Liquids have a definite volume. The particles are constantly moving in random motion.
• Gases don't have a definite shape or volume. The particles move constantly in random directions.
• Nanoparticles have a large surface area to volume ratio.
• Surface area to volume ratio = surface area/volume
• Nanoparticles have a diameter between 1 and 100 nm. They contain only a few hundred atoms.
• Nanoparticles can be useful in:

  • catalysts
  • medicine and drug delivery
  • computing (tiny circuits and chips)
  • silver nanoparticles have antibacterial properties
  • cosmetics
• Although nanoparticles are useful, their full, long term effect on the body is not known.