Shapes of Covalent Molecules VSEPR Theory VSEPR stands

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Shapes of Covalent Molecules

Shapes of Covalent Molecules

VSEPR Theory • VSEPR stands for Valence shell electron pair repulsion theory • It

VSEPR Theory • VSEPR stands for Valence shell electron pair repulsion theory • It describes how the shape of a molecule is determined by the number of pairs of electrons in the outer shell of the central atom in a bond • The electrons will always arrange themselves to be as far apart as possible as the negative charges repel eachother

The Shapes of covalent Molecules

The Shapes of covalent Molecules

Linear A Linear molecule 180° between atoms this will form when there are 2

Linear A Linear molecule 180° between atoms this will form when there are 2 pairs of electrons around the central atom

Trigonal Planar A Trigonal Planar molecule will occur if there are 3 pairs of

Trigonal Planar A Trigonal Planar molecule will occur if there are 3 pairs of electrons around the central atom the electrons are 120° apart

Tetrahedral A tetrahedral molecule will occur if there are 4 bond pairs around the

Tetrahedral A tetrahedral molecule will occur if there are 4 bond pairs around the central atom The electrons are 109. 5° apart

Exceptions • In all the examples we have seen there are no lone pairs

Exceptions • In all the examples we have seen there are no lone pairs of electrons in the outer shell of the central atom • If there are lone pairs they will have a stronger force of repulsion and will change the shape of a molecule • An example is seen in ammonia NH 3

The lone pair of electrons (ie those not involved in a bond) have a

The lone pair of electrons (ie those not involved in a bond) have a strong force of repulsion and cause the shape of the molecule to change

Pyramidal molecules • Ammonia is an example of a pyramidal molecule • This shape

Pyramidal molecules • Ammonia is an example of a pyramidal molecule • This shape occurs if there are 3 bond pairs and 1 lone pair of electrons around the central atom • The bond angle is 107°

V shaped molecules • If there are 2 lone pairs and 2 bond pairs

V shaped molecules • If there are 2 lone pairs and 2 bond pairs around the central atom a v shaped molecule ocurrs • The bond angle in this case is 104. 5°

A table to help you remember Total number of electron pairs Number of bond

A table to help you remember Total number of electron pairs Number of bond Number of lone pairs Shape of molecule 2 2 0 Linear 3 3 0 4 4 0 4 3 1 4 2 2 Trigonal planar Tetrahed -ral Pyramidal Vshaped Examples

Try to use VSEPR theory to deduce the shape of the following molecules •

Try to use VSEPR theory to deduce the shape of the following molecules • • • Be. H 2 Si. Cl 4 PBr 3 CH 4 H 2 O Al. H 3

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