Warmup VSEPR Review VSEPR Review Text pg 56 # 1-10 Text pg 56 # 1-10 You may work with a partner, if you wish. You may work with a partner, if you wish. You may use the mini whiteboards, if you wish. You may use the mini whiteboards, if you wish.

Polar Bonds and Polar Molecules Chemistry 20

Polar Bonds and Polar Molecules Are all molecules that have polar bonds necessarily polar molecules? Are all molecules that have polar bonds necessarily polar molecules? Chemists have found that the existence of polar bonds in a molecule does not necessarily mean that you have a polar molecule. Chemists have found that the existence of polar bonds in a molecule does not necessarily mean that you have a polar molecule. Ex. Carbon dioxide is a nonpolar molecule, even though each of the bonds are polar Ex. Carbon dioxide is a nonpolar molecule, even though each of the bonds are polar

Polar Bonds and Polar Molecules What can be used to predict the polarity of each bond? What can be used to predict the polarity of each bond? Electronegativities may be used to predict the polarity of each bond. Electronegativities may be used to predict the polarity of each bond.

Polar Bonds and Polar Molecules It is customary to show the bond polarity It is customary to show the bond polarity as an arrow, pointing from the positive (  +) to the negative (  -) side of the bond. The arrow represents the bond dipole.

Polar Bonds and Polar Molecules The bond dipole is the charge separation that occurs when the ΔEN of two bonded atoms shifts the shared electrons, making one end of the bond partially positive and the other end partially negative. The bond dipole is the charge separation that occurs when the ΔEN of two bonded atoms shifts the shared electrons, making one end of the bond partially positive and the other end partially negative. The arrow representing a bond dipole points from lower to higher electronegativity The arrow representing a bond dipole points from lower to higher electronegativity

Carbon Dioxide In the case of carbon dioxide, VSEPR theory predicts that it is a linear molecule. In the case of carbon dioxide, VSEPR theory predicts that it is a linear molecule. To determine whether the molecule is a polar molecule, draw the structures and add the arrows that represent polarity. The arrows can be considered to be vectors or lines that show the direction of the polarity of the bonds.

Carbon Dioxide You can determine the polarity of the molecules as a whole by adding the vectors. Because the bonds are identical in CO 2, the polarities of the bonds are the same, and the polarity vectors cancel each other out. The carbon dioxide molecule is non- polar.

Water Water is another molecule that contains polar bonds. In the case of water, however, the molecule as a whole is polar.

Water VSEPR theory predicts that water is a bent molecule. In the water molecule, the horizontal components of the vectors point toward each other, causing them to cancel each other out. The vertical components of the vectors are added to give the final vector.

Water Thus, water is a polar molecule having an oxygen atom with a  - charge and hydrogen atoms with a  + charge. Symmetry helps to determine whether a molecule as a whole should be considered polar or nonpolar. Study Hint: Think of polar as ‘magnetic’ and nonpolar as ‘non-magnetic’.

Carbon Tetrachloride Carbon tetrachloride (CCl 4 ) is a symmetrical tetrahedral molecule with a central carbon atom. All the polar C-Cl bonds are identical. Therefore, the polarities of the four bonds cancel one another and the molecule is non-polar.

Trichloromethane If you replace one of the chlorine atoms with a hydrogen atom, you have trichloromethane (CHCl 3 ), which is polar. The molecule is tetrahedral but since the bonded atoms are not all identical, the bond vectors to do not cancel one another out completely.

Summary: Linear Molecules Bond Polarity: Bond Polarity: Molecular Polarity Molecular Polaritynon-polar Bond Polarity: Bond Polarity: Molecular Polarity Molecular Polaritypolar

Summary: Bent Molecules Bond Polarity: Bond Polarity: Molecular Polarity: Molecular Polarity:polar

Summary: Trigonal Planar Molecules Bond Polarity: Bond Polarity: Molecular Polarity Molecular Polaritynon-polar Bond Polarity: Bond Polarity: Molecular Polarity Molecular Polaritypolar

Summary: Tetrahedral Molecules Bond Polarity: Bond Polarity: Molecular Polarity Molecular Polaritynon-polar Bond Polarity: Bond Polarity: Molecular Polarity Molecular Polaritypolar

Summary: Pyramidal Molecules Bond Polarity: Bond Polarity: Molecular Polarity: Molecular Polarity:polar

Practice Questions 1-3 in your notes Questions 1-3 in your notes Need more? Need more? Text page 59 #11-16 Text page 59 #11-16