Shapes of molecules and ions and Intermediate bonding and bond polarity

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  • Created on: 15-05-14 19:02
Preview of Shapes of molecules and ions and Intermediate bonding and bond polarity

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Shapes of molecules and ions
Electron-pair repulsion theory
- Covalent bonds are directional and have a definite length
- Electron pairs in the outer shell of atoms and ions repel each other and get as far away as possible
Steric number Shape Bond angle With lone pair Two lone pairs
2 180º
(CO, BeCl2)
Bent (107º) NH3 Bent (104.5º) HO
3 120º Lone pairs
- Lone pairs of electrons are
held closer to the nucleus
Trigonal than bonding pairs
planar (BCl3) Trigonal - Therefore they have a
pyramidal (H3O+) stronger repelling effect
- Strength of repulsion
4 109.5º between lone pairs from
high to low: lone-lone > lone-bonding >
- This is why chemicals with 1 lone pair have
smaller bond angles than those with 2
Tetrahedral Bond length and bond angle
(CH4, NH4+) - Bond angle: angle between 2 covalent bonds in
a molecule or giant covalent structure
5 90º and - Bond length: distance between 2 nuclei of 2
120º atoms linked by 1 or more covalent bonds. For
the same 2 atoms, triple bonds are shorter than
double bonds which are shorter than single
Trigonal - Multiple bonds act no different than single ones
bipyramidal when it comes to predicting the shape
6 90º
- Allotrope: different form of the same element in
the same physical state
- Strong covalent bonds- giant molecule
Octahedral - Uses: gemstone; very hard so used
(SF6) for cutting and grinding hard
materials like glass/stone;
conducts thermal energy very
well so doesnt overheat when used for cutting (vibrations of molecules move
rapidly through the entire structure, thus conducting the heat)

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- Giant covalent structure
- High melting point so used to line walls in furnaces and to
make crucibles for molten metals
- Each atom is bonded to 3 others, and the last outer shell
electron becomes delocalised
- Conducts electricity so used for electrodes and as the
positive terminal in dry cells
- Added to composites as fibres to increase tensile strength
- Soft and greasy (bonds between layers are weak so
layers slide over each other) so used as lubricant
-…read more


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