chemistry

• describe how a sigma bond forms and the rotation

  • direct overlap of orbitals directly between the bonding atoms; free rotation of the sigma bond
• explain the tetrahedral shape

  "it has a bond angle of 109.5° and has 4 bonded pairs.

  bonded pair to bonded pair repel less than bonded to lone and lone to lone

  bonded pairs repel equally"
• what happens to the bp of alkanes when you increase chain length

  • the longer the chain, the higher the boiling point due to more london dispersion forces (more electrons and greater surface area) so there is more energy needed to overcome the london dispersion forces
• what happens to the bp when an alkane is more branched?

  • a branched alkane has less surface area contact between molecules.
  • so there are fewer london dispersion forces and therefore less energy is needed to break the london dispersion forces
• alkanes completely combust to give... fuel + oxygen -> carbon dioxide + water
• alkanes incompletely combust to give... fuel + oxygen -> carbon monoxide + water
• what conditions are needed for free radical substitution

  • UV light (include in equation above arrow) excess alkane to reduce further substitution
• free radical substitution turns what compound into what? alkane to haloalkane
• what are limitations of free radical substitution

  - mixture of products substitution at different positions along chain further substitution
• what type of bonds are present in alkenes and rotation?

  a pi and sigma bond; restricted rotation of the pi bond
• explanation of trigonal planar shape

  it has a bond angle of 120°. it has 3 bonded pairs which repel equally"
• what is the difference between E/ Z isomerism and cis-trans isomerism

  • with cis-trans isomerism the groups attached to the carbon must be the same whereas with e/z it doesn't matter.
• what are the Cahn-Ingold-Prelog priority rules?

  • the higher the atomic number, the higher the priority.
  • if the atomic number is the same you look for the first point of difference.
  • the higher the atomic number at the point of difference gains higher priority as a branch
• 3BP & 1LP trigonal pyramidal
• 2BP & 2LP non-linear
• 2BP linear
• 3BP trigonal planar
• 4BP tetrahedral
• 5BP trigonal bipyramidal
• 6BP octahedral
• 2 regions of electron density linear
• 3 regions of electron density trigonal planar
• isotope

  atoms of the same element with the same number of protons, different number of neutrons
• relative atomic mass

  • weighted mean mass of an atom (of an element) compared with 1/12th the mass of a carbon-12 atom
• ionic bonding

  • strong electrostatic forces of attraction between oppositely charged ions
• giant ionic lattice regular & repeating 3D arrangement of ions in an ionic compound
• covalent bonding strong electrostatic forces of attraction between a shared pair of electrons & the positive nuclei of the bonded atoms
• dative covalent bond shared pair of electrons with the bonded pair of electrons donated from the same atom
• average bond enthalpy the energy needed to break 1 mole of bonds in the gas phase averaged over many different compounds
• orbitals an orbital is a region around the nucleus that can hold up to 2e- with opposite spins
• electronegativity the ability of an atom to attract the bonding pair of electrons in a covalent bond
• polar bonds they exist due to differences in electronegativity, the greater the difference the polar bond
• hydrated crystalline form of a substance that contains water molecules
• anhydrous crystalline form of a compound containing no water molecules
• water of crystallisation refers to water molecules forming an essential part os a crystalline structure
• hydrated meaning crystalline form of a substance that contains water molecule
• what is a functional group? a group of atoms responsible for the characteristic reactions of a compound
• what is a homologous series? a series of organic compounds having the same functional group but with each successive member differing by ch2
• what is an empirical formula the smallest whole number ratio of elements from the structural formula present in the compound
• what is an aliphatic compound? - a compound containing carbon and hydrogen joined together in straight chains, branched chains / no aromatic rings.- can only be an alkane, alkene or alkyne.