Molecular Geometry Lab

Valence electrons are the outermost s and p electrons in an atom and are usually the

electrons involved in chemical bonding. A way for visually representing these electrons

was developed by the American chemist G.N. Lewis. A Lewis dot symbol consists of the

abbreviation for the element and dots for each valence electron placed on fours sides of

the abbreviation. Up to two electrons can be placed on each side, providing for eight

electrons. The octet rule reflects this in the fact that atoms will do what they need to in

order to have eight valence electrons. This number of valence electrons provides for full

s and p orbitals just like the stable electron configuration of a noble gas.

Lewis structures show the arrangement and bonding of atoms in compounds. In such

structures, unbonded electrons are shown as dots and shared electrons are often shown as

a line between atoms. Two pairs of shared electrons are shown as two lines (a double

bond) and three pairs of shared electrons are shown as three lines (a triple bond). In

drawing Lewis structures, there are some general rules to follow:

1. Sum the valence electrons from all atoms.

2. Write the symbols for the atoms to show which atoms are attached to which, and

connect them with a single bond.

3. Complete the octets of the atoms bonded to the central atom.

4. Place any leftover electrons on the central atom.

5. If there are not enough electrons to give the central atom an octet, try multiple

bonds.

The VSEPR theory describes how electron pairs will arrange themselves in order to

minimize repulsions. Pairs of electrons around the central atom, including bonding and

lone pairs, influence the shape of the molecule because of these repulsions. These pairs

are referred to as areas of electron density or electron domains. Two areas of electron

density will give a linear shape, three areas a trigonal planar shape, and four areas a

tetrahedral shape. The arrangement of these electron densities is referred to as the

electronic geometry. The resulting arrangement of atoms is referred to as the molecular

geometry.

Objectives

1. To become familiar with Lewis structures, the VSEPR theory, and

three-dimensional structures of molecules.

Procedure I

Tie balloons together to indicate central atoms with 2, 3, and 4 areas of

electron density. Insert pictures of your representations. On your pictures,

label the value of the angle between neighboring areas of electron density.

Also, label the electronic geometry for each.

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Valence electrons are the outermost s and p electrons in an atom and are usually the electrons involved in chemical bonding. A way for visually representing these electrons was developed by the American chemist G.N. Lewis. A Lewis dot symbol consists of the abbreviation for the element and dots for each valence electron placed on fours sides of the abbreviation. Up to two electrons can be placed on each side, providing for eight electrons. The octet rule reflects this in the fact that atoms will do what they need to in order to have eight valence electrons. This number of valence electrons provides for full s and p orbitals just like the stable electron configuration of a noble gas. Lewis structures show the arrangement and bonding of atoms in compounds. In such structures, unbonded electrons are shown as dots and shared electrons are often shown as a line between atoms. Two pairs of shared electrons are shown as two lines (a double bond) and three pairs of shared electrons are shown as three lines (a triple bond). In drawing Lewis structures, there are some general rules to follow:

Sum the valence electrons from all atoms.
Write the symbols for the atoms to show which atoms are attached to which, and connect them with a single bond.
Complete the octets of the atoms bonded to the central atom.
Place any leftover electrons on the central atom.
If there are not enough electrons to give the central atom an octet, try multiple bonds. The VSEPR theory describes how electron pairs will arrange themselves in order to minimize repulsions. Pairs of electrons around the central atom, including bonding and lone pairs, influence the shape of the molecule because of these repulsions. These pairs are referred to as areas of electron density or electron domains. Two areas of electron density will give a linear shape, three areas a trigonal planar shape, and four areas a tetrahedral shape. The arrangement of these electron densities is referred to as the electronic geometry. The resulting arrangement of atoms is referred to as the molecular geometry.