Shapes of molecules - B & forces Pt 1 Chemistry (UNIT 2)
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What does molecular shape depend upon?
Electron pairs around the central atom.
Describe the electron-pair repulsion theory?
- Electron pairs repel each other because they are negative.
- Type of electron pair affects how much it repels other electron pairs. (Lone pairs repel more than bonding pairs.)
How are the bonds arranged in any single-bonded carbon atom?
- Tetrahedral shape
- Angle between any two covalent bonds is 109.5o
What is the shape and bond angle of a molecule with 2 electron pairs on a central atom? eg. BeCl2 and CO2?
Give 4 examples of molecules with 120o bond angles (3 electron pairs).
Why is the bond angle still 120o
Because the extra electron density in the double bonds cancels out the extra repulsion from lone pair.
What is the shape and bond angle of BCl3, CO32- , NO3- ?
What is the shape and bond angle of an alkane? (eg. methane, propane)
What is the shape and angle of NH4+ ?
What is the shape and bond angles of NH3 and SO32- ? Why?
- Trigonal pyramidal
- 107oBecause of one lone pair of electrons
What is the shape and bond angle of water? Why?
- Non-linear or "bent"
- 104.5oBecause of 2 lone pairs of electrons
What is the shape and bond angles of PCl5 ?
- Trigonal bipyramidal
- 90o & 120o
What is the shape and bond angle of SF6 ?
What are the 3 possible combinations of electron pairs? Give them in order of size of bond angle.
- Lone-pair/lone-pair bond - angles biggest
- Bonding-pair/bonding-pair - angles smallest
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