topic 2

• an ion is a charged particle ionic bonding is between a metal and a non - metal
• ionic compounds

  1. giant lattice structure
  2. strong electrostatic forces of attraction meaning high melting and boiling point
  3. free moving ions so can conduct electricity when in liquid or gas form
• metals have high melting points because they require a lot of energy to break the strong electrostatic forces of attraction between the positively charged metal ions and the negatively charged electron cloud.
• metallic bonds are formed by the delocalised electrons moving freely through the sea of positive charges (the metallic lattice)
• metal atoms lose their outer shell of electrons when forming an ionic compound, so metals always form cations
• the giant lattice structure means that there are lots of positive charges which attract negative charges from other molecules, this makes it easy for them to dissolve in water as the water molecule has a partial charge on it due to its polar nature
• covalent bonding occurs between two atoms sharing one or more pairs of electrons
• a single covalent bond forms when two atoms share one pair of electrons
• covalent bonding occurs between two non-metals
• double covalent bonds occur when two atoms share two pairs of electrons
• in a covalent bond, both atoms contribute at least one electron to the shared pair(s) of electrons
• ionic compounds have high melting points because they contain strong electrostatic attractions between oppositely charged ions
• molecular substances have low melting points because they do not contain strong forces holding them together
• simple molecular structure

  1. mostly gas and liquid at room temperature
  2. low melting and boiling point
  3. held together by strong covalent bonds
  4. easily separated as you only need to break intermolecular forces
  5. dont conduct electricity
• in polymers small units are linked to make bigger molecules with repeating units which are joined with covalent bonds
• in polymers they have a larger intermolecular force then covalent bonds so have a higher melting and boiling point and are usually solid at room temperature
• polymers have a weaker intermolecular force than ionic bonds so they have a lower boiling and melting point than giant molecular compounds
• in a giant covalent structure all bonds are covalent
• giant covalent structures

  1. high melting and boiling point because lots of energy is needed to break bonds
  2. dont conduct electricity as no free moving ion
• diamond has 4 covalent bonds
• graphite has 3 covalent bonds
• graphene has 3 covalent bonds
• fullerene has 3 covalent bonds
• diamond is a giant covalent structure made of carbon atoms with strong covalent bonds
• diamond has a high melting point as a lot of energy s needed to break the bonds
• diamond doesn't conduct electricity as ii has no free moving electrons
• graphite is a giant covalent structure of hexagonal rings of carbon atoms held together by weak covalent bonds
• graphite is a sheet of carbon atoms
• graphite has no bonds between layers so they can easily slide over each other making them soft and slippery and ideal for lubricants
• graphite has a high melting and boiling point
• in graphite each atom has 1 delocalised electron so it conducts heat and electricity
• graphene is a single layer of graphite, it is a single layer of carbon atoms bonded together in a honeycomb structure
• graphene is made of a network of covalent bonda making it very strong and light so it is added to composite materials to improve strength without adding weight
• graphene contains delocalised electrons so can conduct electricity
• fullerene is molecules of carbon close together like closed tubes or hollow balls
• fullerenes can be used for caging other molecules
• fullerenes can be used as an industrial catalysts as they have a huge surface area
• fullerenes are great lubricants
• fullerenes can be used for

  1. nanotubes which are tiny carbon cylinders
  2. high ratio between length and diameter
  3. conduct electricity
  4. high tensile strength
  5. nanotechnology - technology that uses small particles like nanotubes
• electrostatic forces are between metal atom and delocalised electrons