Topics: Chemical bond, Covalent bond, Atom Pages: 4 (757 words) Published: February 17, 2013
2.3 Shapes of molecules and ions
2.3a Electron pair repulsion theory
a demonstrate an understanding of the use of electron-pair repulsion theory to interpret and predict the shapes of simple molecules and ions In a chemical species like a molecule or ion, pairs of electrons create negative centres that surround the central atom. These electron pairs repel each other and arrange themselves to be as far apart as possible, thus minimising repulsion. [pic](source:

Lone pairs repel more strongly than bonding pairs of electrons therefore a lone pair distorts the shape of a molecule.   Nitrogen has 5 outer electrons so ammonia will have four electron pairs around the central nitrogen atom and be tetrahedral with respect to electron pairs.  Ammonia, NH3 has a lone pair which generates more repulsion than the 3 bonding pairs of electrons.  The shape of NH3 is therefore distorted tetrahedral.

2.3b Known molecular shapes
b recall and explain the shapes of BeCl2, BCl3, CH4, NH3, NH4+, H2O, CO2, gaseous PCl5 and SF6 and the simple organic molecules listed in Units 1 and 2 |molecule |shape wrt negative centres |shape wrt atoms |bonds and lone pairs around central atom | |BeCl2 |linear |linear |2 single bonds | |CO2 |linear |linear |2 double bonds | |HCl |tetrahedral |linear |1 single bond, 3 lone pairs | |BCl3 |trigonal planar |trigonal planar |3 single bonds | |CH4 |tetrahedral |tetrahedral |4 single bonds...
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