Elements of life

• 2 bond pairs, 0 lone pairs


  Linear

  180°

  e.g. BeCl2

  
• 3 bond pairs, 0 lone pairs

  Trigonal Planar

  120°

  e.g. BF3

  
• 2 bond pairs, 1 lone pair

  Bent

  118°

  e.g. NO2

  
• 4 bond pairs, 0 lone pairs

  Tetrahedral

  109.5°

  e.g. CH4

  
• 3 bond pairs, 1 lone pair

  Pyramid

  107°

  e.g. NH4

  
• 2 bond pairs, 2 lone pairs

  Bent

  104.5°

  e.g. H2O
• 5 bond pairs, 0 lone pairs


  Trigonal Bipyramid

  120°,90°

  e.g. PCl5

  
• 6 bond pairs, 0 lone pairs


  Octahedral

  90°

  e.g. SF6

  
• In 1803 John Dalton said...


  That all atoms are SPHERES and all elements are made from different spheres
• Plum pudding model


  In 1897 J.J Thompson discovered the electron and said there were negative electrons "plums" in a positive "pudding"

  
• Gold Leaf Experiment


  1909, Ernest Rutherford.

  Fired positive alpha particles at gold leaf. Most went through to other side, some deflected back.

  He concluded that the atom had a very small positively charged nucleus and a negative cloud of empty space.
• Electron shell discovery


  1913, Niels Bohr.

  Found a problem with previous model (electrons would collapse into positive nucleus). He fired EM radiation at atoms EM is absorbed by electrons and they move up an energy level and emit it when they drop back down.
• Nuclear fusion


  -2 nuclei fuse together to make a heavier molecule

  -happens in the sun and other stars

  -needs VERY HIGH TEMPERATURES AND PRESSURES to overcome repulsive forces.

  E.g. H+H -> He
• s subshell


  1 orbital, can hold 2 electrons

  
• p subshell


  3 orbitals, can hold 6 electrons

  
• d subshell


  5 orbitals, can hold 10 electrons
• f subshell


  7 orbitals, can hold 14 electrons
• Spin pairing


  When 2 electrons occupy 1 orbital they 'spin' in opposite directions
• S orbital shape


  Spherical

  
• P orbital shape


  Px, Py and Pz

  
• What does 1s2 mean?

  1 is the energy level (period)

  s is the orbital type

  2 is the number of electrons in orbital
• Find the electron configuration of iron (Fe)

  1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2

  
• Electron blocks

  
• What is ionic bonding?

  Oppositely charged ions held together by electrostatic attractions

  
• Hydroxide ion


  OH -
• Ammonium ion


  NH4 +
• Carbonate ion


  CO3 2-
• Nitrate ion


  NO3 -
• Sulfate ion


  SO4 2-
• Giant ionic structure


  Regular structure, cubic shape and giant repeating pattern.

  e.g. sodium chloride

  
• Ionic compounds


  -high melting and boiling point ( because strong electrostatic attractions between ions)

  -most are soluble in water (because water molecules are polar and can attract ions to break up the structure)

  -hard and brittle

  e.g. Lithium hydroxide
• What is covalent bonding?


  Shared pair(s) of electrons

  
• Covalent compounds


  -low melting and boiling points ( because strong forces between atoms but weak forces between molecules)

  -soft and flexible (normally)

  -don't conduct electricity when dissolved in water

  e.g. ethanol, CO2, methane (CH4)
• Diamond


  -giant covalent structure

  -each carbon is bonded to four other carbon atoms

  -high melting point

  -doesn't conduct electricity

  -insoluble

  -very hard
• Graphite


  -giant covalent structure

  -each carbon is bonded to three other carbon atoms, in layers

  -high melting point

  -soft, slippery, used in locks and pencils

  -conducts electricity ( has delocalised electrons)

  -insoluble

  -used in pencils and as a lubricant

  
• Silicon dioxide


  -giant covalent structure

  -same as diamond but one oxygen between each silicon bond

  -high melting point

  -hard

  -doesn't conduct electricity

  -insoluble

  
• What is metallic bonding?


  Giant lattice structure of positive ions in a sea of delocalised electrons

  
• Metallic structures


  -high melting and boiling points (except for group 1 metals because they have large atoms and don't form as many bonds)

  -conduct electricity (because delocalised electrons can carry a charge)

  -conduct heat

  -malleable and ductile

  -insoluble
• Bohr's theory


  When an atom becomes excited (absorbs energy) it moves up to a higher energy level and when it eventually comes back down it emits extra energy as EM and gives off an emission spectrum
• Emission spectra


  Shows the frequency of light given out when an electron moves down energy levels. Appear as coloured lines on a black background.