Molecular shapes and DipolesKnowledge of shapes of a molecule are important for

determining functions and activity of molecules. Example: proteins enzymes of a particular shapes serve

a particular function and activity because an enzyme’s shape(key) is will only fit one other substrate( lock).

General outcome: In this lesson, students will describe

the roles of modelling and use theory of modelling in explaining and predicting the structure, bonding and

properties of ionic and molecular substances.

Knowledge of shapes of a molecule are important for determining functions and activity of molecules. Example: proteins enzymes of a particular shapes serve a particular function and activity because an enzyme’s shape(key) is will only fit one other substrate( lock)

Molecular shapes cont’d General learner outcomes

Specific learner outcomes

20–A2.1k recall principles for assigning names to molecular substances.

20–A2.3k relate electron pairing to multiple and covalent bonds

20–A2.2k explain why formulas for molecular substances refer to the number of atoms of each

20–A2.4k draw electron dot diagrams of atoms and molecules, writing structural formulas for

molecular substances and using Lewis structures to predict bonding in simple molecules

20–A2.5k apply VSEPR theory to predict molecular shapes for linear, angular (V-shaped, bent),

tetrahedral, trigonal pyramidal and trigonal planar molecules

Teaching Department Professor:

Dr. Carbonaro

Lab Instructor

Teaching Assistants

Jeff Chu, Jackson Warner

Head marker

Marking Assistnats

EDIT Course: Mark Weighting

FinalLabsMidterm

Using VSEPR to predict shapes… Valence-shell-electron-pair-replusion theory was designed by Linus Pauling in

the late 1930s. The theory was based on the electron repulsion created by lone electrons and bonding electron that surround the central atom of a molecular structure.

According to VSEPR theory:   Only the valence e- of the central atom are important in determining the

overall shape of a molecule.   Valence e- are paired in a molecule or polyatomic ion.   Bonded pairs of electrons and lone pairs of e- are treated equally.   Valence e- repel one another (very important)   Finally, the molecular shape is determined by the positions of the electron

pairs when they are maximum distance apart

Drawing Lewis structures First, consider all electronegative atoms and

place the atom with lowest electro negativity in the center of structure.

Place atoms of high electro negativity around the central atom.

Count the total number of e- and subtract this from the e- already present in structure.

Finally, place all ‘left over’ electrons on the central atom.

VSEPR theory continued…Key concepts to consider when drawing

stuctures to determine shape. 1. First draw the Lewis dot diagram and

consider ALL arrangement. 2. Draw any left over electron in a way that

they are far apart from one another so that repel each other.

3. Before determining shape look at the central atom (noted by letter A), then at other surrounding bonded atoms (noted by letter X), then finally lone pairs (noted by letter E)

VSEPR AX2- denotes as having 1 central atom, 2 surrounding

bonding atoms and zero lone pairs. Shape: linear. Example: CO2

AX3- 1 central atom, 3 bonding atoms, zero lone pairs. Shape: trigonal planar. Example: BH3

AX4: 1 central atom, 4 bonding atoms, zero lone pairs. Shape: tetrahedral. Example: CH4, SiH4.

AX3E1: 1 central atom, 3 bonding atoms, 1 lone pair. Shape: Trigonal pyramidal. Example: NH3

AX2E2- I central atom, 2 bonding electrons, 2 lone pairs. Shape: angular or bent-shaped. Example: H20

AX3E1- I central atom, 1 bonding atom, 3 lone pairs. Shape: linear. Example: HCl

Guided practiceExample 1 – Draw sulfur dioxide. Include

number of bonding atoms, lone pairs and VSEPR shape.

Example 2- Draw chloromethane. Include number of bonding atoms, lone pairs and VSEPR shape.

Example 3 – Draw oxygen. Include number of bonding atoms, lone pairs and VSEPR shape.

YouTube - Chemistry VSEPR Theoryhttp://www.youtube.com/watch?v=i3FCHVlSZc4