Unit 1

Unit 1

1. Electrons, bonding and structure

   • ionisation energy
     • factors influencing it:
       • nuclear charge
         • : a large nuclear charge means the outer electron is difficult to remove, so the inisation energy is large
       • atomic radii
         • in larger atoms the outer most electron is father away from the nucleus and so is less attracted, so therefore easier to remove
       • Electron shielding
         • if more inner electron shells shield the nuclear charge from the outer electron, it will be easier to remove and therefore a low ionisation enery
     • first ionisation energy defintion
       • the energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of 1+ ions
     • across a period
       • a general increase: increasing nuclear charge smaller atomic radii similar shielding
     • down a group
       • general decrease: larger atomic radii more shielding larger nuclear charge is outweighed by the previous two factors
   • ionic bonding
     • bonding between non metals and metals electrostatic attraction between two oppositely charged ions arises when an electron is transferred from one atom to another.
   • covalent bonding
     • bonding between non-metals sharing of a pair of electrons between two atoms, with one electron being donated from each atom
   • dative covalent bond
     • same as a covalent bond, however the shared electrons are both donated from one of the atoms in the bond.
   • bonding angles
     • linear: 180 non linear: 104.5 Pyramidal: 107 tetrahedral: 109.5 octahedral: 90 trigonal bipyramidal: 90 and 120 trigonal planar: 120 Lone pair of electrons>bonded pair
   • polarisation
     • covalently bonded. bond polarisation is when the bond had become slightly ionic in character because it has a dipole moment. between a slightly negative and slightly positive atom bonding.
   • intermolecular forces
     • van der waals forces
       • instantaneous dipole between polar bond induces an instantaneous dipole in neighbouring molecule
     • permanent dipole-dipole forces
       • occurs between molecules with permanent dipoles, a slightly negative atom on one molecule attracts the slightly positive atom on another molecule causing electrostatic forces to occur
     • hydrogen bonding
       • relatively strong type of permanent dipoleoccuring between a molecule with H and O, N or F
   • water
     • has a high surface tension and forms a meniscus because the hydrogen bonds pull the water surface downwards
     • ice lower density than water
       • a whole network of hydrogen bonds, and are kept apart to form a littice by this arrangement, giving a lot of space in the structure making ice lower density than water