VSEPR

Question 1

VSEPR

Answer 1

Valence shell electron pair repulsion (VSEPR) is a model for predicting molecular shape. The principle is that each group of valence electrons (domains) is located as far as possible from the others in order to minimise repulsion It works best for covalent molecules and polyatomic ions with a single central atom.

Question 2

Determinants of Molecular shape

Answer 2

• number of lone pairs and bonding pairs around the central atom
• need to be determined by drawing Lewis electron diagram
• electron pairs repel other electron pairs

Question 3

Domains

Answer 3

Domains are the “groups” of valence electrons around an atom. When we are talking about domains, we primarily talk about domains around the centre of the atom. They include bonding electrons and lone pairs. A single bond, double bond or triple bond count as a single domain.

Question 4

Two Domain Molecules

Answer 4

The furthest apart that two domains can be is 180 degrees (opposite sides of a central atom, eg. CO2). Electron geometry is called linear. If all of the domains are bonding domains, they molecular geometry is also linear.

Question 5

Two Domain Molecules

Answer 5

The furthest apart that two domains can be is 180 degrees (opposite sides of a central atom, eg. CO2). Electron geometry is called linear. If all of the domains are bonding domains, they molecular geometry is also linear.

Question 6

Three Domain Molecules

Answer 6

The furthest apart these three domains can be is 120 degrees. Examples include BF3. This is called trigonal planar. If all the domains are bonding domains, then the electron geometry (considers ALL the domains) is also trigonal planar. If there is one lone pair and two bonding pairs (O3), the molecular geometry is called bent.

If there are only three atoms in the molecule/ion, there is 2 ways they can be arranged. Either they are in a straight line and it is linear, or they are not in a straight line and the shape is bent (regardless of angle).

Question 7

Four Domain Molecules

Answer 7

The furthest apart that four domains can be is 109 degrees. The electron geometry (lone and bonded pairs) is tetrahedral. If all pairs are bonding pairs, then the molecular geometry is also tetrahedral. If 3 bonded, 1 lone pair molecular geometry is trigonal pyramidal. If 2 bonded and 1 lone pair molecular geometry is bent.

You can’t arrange four domains in anyway that two of those domains are 180 degrees away from each other. So if you have four domains, you never get a linear shape.