CHEMISTRY 10-12 HANDOUT Cairo American College 2012/2013 Unit 4 Chemical Bonds SHAPES OF MOLECULES THE VSEPR THEORY VSEPR Valence Shell Electron Pair Repulsion theory Each atom is surrounded by electron pairs – these can be lone (unattached) pairs or bonded (attached) pairs. e.g. PCl 3 . These e- pairs take the form of an e- cloud. Lone pairs e- clouds are larger The VSEPR Theory : e- pairs around each atom will repel each other to minimize repulsion they will arrange themselves so that they are as far apart from each other as possible Note that the 4 e-‘s in a double bond form a single e- cloud. So do the 6 e-s in a triple bond SHAPES OF MOLECULES If there are 2 electron clouds around a central atom, shape will be linear (180 o ). Example MgBr 2 If there are 3 electron clouds around a central atom, shape will be trigonal planar (120 o ). Example AlCl 3 If there are 4 electron clouds around a central atom, shape will be tetrahedral (109.5 o ). Example CH 4 If there are 4 electron clouds around a central atom, but one of them is a lone pair , shape will be trigonal pyramid (107 o ). Example NH 3 Angle is smaller because lone pairs take up more space, causing squeezing of the 3 bonded pairs If there are 4 electron clouds around a central atom, but two of them are lone pairs , shape will be angular (104.5 o ). Example H 2 O Angle is even smaller because of the presence of two lone pairs, causing even more squeezing of the 2 bonded pairs Try the following: CO 2 , SO 3 , PbCl 4 , AsBr 3 , SCl 2 , CO 3 -2

Hdt 4d Shapes of Molecules

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CHEMISTRY 10-12 HANDOUT Cairo American College 2012/2013 Unit 4 Chemical Bonds

SHAPES OF MOLECULES THE VSEPR THEORY VSEPR Valence Shell Electron Pair Repulsion theory Each atom is surrounded by electron pairs these can

be lone (unattached) pairs or bonded (attached) pairs. e.g. PCl3.

These e- pairs take the form of an e- cloud. Lone pairs e- clouds are larger The VSEPR Theory: e- pairs around each atom will

repel each other to minimize repulsion they will arrange themselves so that they are as far apart from each other as possible

Note that the 4 e-s in a double bond form a single e- cloud. So do the 6 e-s in a triple bond

SHAPES OF MOLECULES If there are 2 electron clouds around a central atom,

shape will be linear (180o). Example MgBr2

If there are 3 electron clouds around a central atom, shape will be trigonal planar (120o). Example AlCl3

If there are 4 electron clouds around a central atom, shape will be tetrahedral (109.5o). Example CH4

If there are 4 electron clouds around a central atom, but one of them is a lone pair, shape will be trigonal pyramid (107o). Example NH3

Angle is smaller because lone pairs take up more space, causing squeezing of the 3 bonded pairs

If there are 4 electron clouds around a central atom, but two of them are lone pairs, shape will be angular (104.5o). Example H2O

Angle is even smaller because of the presence of two lone pairs, causing even more squeezing of the 2 bonded pairs

Try the following: CO2 , SO3 , PbCl4 , AsBr3 , SCl2 , CO3-2