Molecular Modeling

Topics: Atom, Electron, Chemical bond Pages: 3 (626 words) Published: November 30, 2012

1. Objectives
● Predictthe shape of identified compounds;
● Construct molecular models of identified compounds; and ●Determine the molecular structure of identified compounds. 2. Theory
Building models of molecules are useful for visualizing how atoms are connected in three-dimensional space called molecular geometry, which is best predicted by Valence-Shell Electron-Pair Repulsion (VSPER) theory. The following are the sets of rules summarizing thsi theory:

● Consider molecules and ions where two or more atoms are bonded to a central atom. ● The electron pairs in the valence shell of the central atom are assumed to position as far apart as possible because electron pair repels one another. The shape of the molecule or ion is a result of the electron-pair repulsion. ● All the valence-shell electron pairs of the central atom are considered both the pairs that form covalent bonds (called bonding pairs) and the pairs that are unshared (called nonbonding pairs or lone pairs). ● The nonbonding pairs help to determine the position of the atoms in the molecule or ion.

Valence –Shell-Electron-Pair Repulsion (VSEPR) theory allows the chemist to predict 3-dimensional shape of molecules from knowledge of their Lewis Dot Structure. In VESPR theory, the position of bound atoms (ligands0 and electron pairs are described relative to a central atom. Once the ligands and lone pair electrons are positioned, the resulting geometrical shape presented by the atoms only (ignoring lone pairs) is used to describe the molecule. Electron Density and Molecular Geometry | d(Be-Cl) = 0,117 nm = 180 °| | |


d(B-F) = 0,130 nm  = 120 °
Triangular Planar

d(S-O) = 0,150 nm  = 109 .5°

| | d(P-Cléq) = 0,202 nmd(P-Clax) = 0,214 nm(ClPCl) = 90 ° ;  (ClPCl) = 120 °|
Triangular Biplanar
| | d(Xe-F) = 0,190 nm = 90°|

3. Apparatus and Materials
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