Bonding, Structure, and the Properties of Matter

• chemical bonds

  there are three types of chemical bonds: ionic, covalent, metallic

  • ionic - particles are oppositely charged, occurs in compounds formed from metals + non-metals.
  • covalent - particles are atoms which share pairs of electrons, occurs in most non-metallic elements an compounds.
  • metallic - particles are atoms which share delocalised electrons, occurs in metallic elements and alloys.
• ionic bonding


  metal + non-metal: electrons in the outer shell of the metal atom are transferred.

  • metal atoms lose electrons to become positively charged ions.
  • non-metal atoms gain electrons to become negatively charged ions.
  • an ion is an atom that has lost/gained electrons.
• ionic compound 


  • a giant structure of ions
  • held together by strong electrostatic forces of attraction.
  • forces act in every direction
• covalent bonding


  • when atoms share one or more pairs of electrons
  • polymers are large covalently bonded molecules
  • giant covalent structures consist of many atoms in a lattice structure.
  • diagrams to show can be dot and cross
• metallic bonding


  • bonding consists of positive ions and delocalised electrons arranged in a regular pattern
  • delocalised electron system consists of the electrons lost from the atoms to form positive ions
  • delocalised electrons are free to move through the structure.
  • metallic bonds are strong as the electrons are shared through the structure.
• the three states of matter


  solid, liquid, and gas

  • melting and freezing take place at the melting point.
  • boiling and condensing take place at the boiling point.

  
• state symbols


  the three states of matter are shown as solid (s), liquid (l), gas (g), and (aq) for aqueous solutions.
• properties of ionic compounds


  • have regular structures where there are strong electrostatic forces of attraction in all directions between oppositely charged ions.
  • high melting and boiling point because lots of energy is needed to break the bonds.
  • conduct electricity in water but cant conduct electricity in solid.
• properties of small molecules


  usually gasses or liquids with low boiling and melting points.

  • weak intermolecular forces between the molecules, broken when boiling or melting (not covalent)
  • intermolecular forces increase as molecules grow so larger molecules have higher boiling/melting points.
  • dont conduct electricity, as small molecules dont have an overall electric charge.
• polymers


  • have very large molecules
  • atoms are linked to other atoms by strong covalent bonds.
  • intermolecular forces between polymers are strong so solid at room temperature
• giant covalent structures


  solids with high melting points

  • linked to other atoms by strong covalent bonds - must be overcome to melt or boil substances.

  e.g. diamond, graphite, silicon dioxide
• properties of metals and alloys


  giant structures of atoms with strong metallic bonding.giant structures of atoms with strong metallic bonding.

  • most have high melting/boiling points
  • can be bent and shaped as atoms can slide over each other.

  alloys are made from 2 or more different types of metals

  • different sized atoms distort the layers in the structure, so alloys are harder than pure metals
• metals as conductors 


  good conductors of electricity as delocalised electrons carry electrical charge through the metal.

  good conductors of thermal energy as energy is transferred by the delocalised electrons.
• diamond

  each carbon is joined to four other carbons covalently.

  • its very hard, has a high melting point, and does not conduct electricity.

  
• graphite 


  each carbon is covalently bonded to three other carbons, forming layers of hexagonal rings which have no covalent bonds between the layers.

  • layers can slide over each other and have weak intermolecular forces. graphite is soft and slippery.

  one electron is delocalised

  • graphite is similar to metals and can conduct electricity
• graphene an fullerenes 


  graphene :

  • single layer of graphite
  • useful in electronics and composites
  • very strong because atoms are tightly bonded.

  carbon can form fullernes with different numbers of carbon atoms.

  • carbon with hollow shapes
  • may contain rings with five or seven carbon atoms
  • first fullrene to be discovered is C60 which is spherical.
• nanoparticles 


  • are 1-100 nanometres across
  • as the side of the cube decreases by a factor of 10, the surface area to volume ratio increases by a factor of 10.
  • involve fullerenes
  • has different properties to the bulk chemical its made from. smaller quantities are needed because of smaller SA:V
• uses of nanoparticles 


  • good catalysts as have high SA:V ratio.
  • used to produce highly selective sensors
  • suntan cream, deoderants
  • conduct electricity so can be used in small electrical circuits in computers.
  • concerns that they may be toxic and enter brain via bloodstream and cause harm.