Exercises 6. trigonal planar 7. bent 8. trigonal pyramidal 9. T-shaped 10. square planar

E denotes a lone pair

E denotes a lone pair

Polar bonds and polar molecules

Polar bonds and polar molecules When two identical atoms form a covalent bond, as in H2 or Cl2, each atom has an equal share of the electron pair in the bond.

Polar bonds and polar molecules When two identical atoms form a covalent bond, as in H2 or Cl2, each atom has an equal share of the electron pair in the bond. The electron density at both ends of the bond is the same because the electrons are equally attracted to both nuclei.

When different kinds of atoms combine (e. g When different kinds of atoms combine (e.g. HCl) the attractions are not equal.

When different kinds of atoms combine (e. g When different kinds of atoms combine (e.g. HCl) the attractions are not equal. In the HCl molecule the bonding electron cloud is pulled more tightly around the Cl and that end of the molecule experiences a slight buildup of negative charge.

When different kinds of atoms combine (e. g When different kinds of atoms combine (e.g. HCl) the attractions are not equal. In the HCl molecule the bonding electron cloud is pulled more tightly around the Cl and that end of the molecule experiences a slight buildup of negative charge. In HCl electron transfer is incomplete. The electrons are still shared, but unequally.

When different kinds of atoms combine (e. g When different kinds of atoms combine (e.g. HCl) the attractions are not equal. In the HCl molecule the bonding electron cloud is pulled more tightly around the Cl and that end of the molecule experiences a slight buildup of negative charge. In HCl electron transfer is incomplete. The electrons are still shared, but unequally. The charges on either end of the molecule are less than full +1 (on H) and -1 (on Cl) – they are partial charges indicated by a Greek letter delta δ.

When different kinds of atoms combine (e. g When different kinds of atoms combine (e.g. HCl) the attractions are not equal. In the HCl molecule the bonding electron cloud is pulled more tightly around the Cl and that end of the molecule experiences a slight buildup of negative charge. In HCl electron transfer is incomplete. The electrons are still shared, but unequally. The charges on either end of the molecule are less than full +1 (on H) and -1 (on Cl) – they are partial charges indicated by a Greek letter delta δ. H Cl δ+ δ-

The situation for H2, compared with F2, and HF.

A bond that carries partial positive and negative charges at opposite ends is called a polar bond.

A bond that carries partial positive and negative charges at opposite ends is called a polar bond. The polar bond in HCl results because the bond has poles of opposite charge at either end: the molecule is said to be a dipole.

A bond that carries partial positive and negative charges at opposite ends is called a polar bond. The polar bond in HCl results because the bond has poles of opposite charge at either end: the molecule is said to be a dipole. The extent of the polarity of a molecule is expressed quantitatively through its dipole moment.

Dipole moment: A measure of the charge separation in a molecule: the product of the charge and the distance between the charges:

Dipole moment: A measure of the charge separation in a molecule: the product of the charge and the distance between the charges: where is the dipole moment, Q is the charge, and r is the separation distance.

Dipole moment: A measure of the charge separation in a molecule: the product of the charge and the distance between the charges: where is the dipole moment, Q is the charge, and r is the separation distance. When there are a number of different charges, it is necessary to sum over all the charges (we will not deal with this case).

Dipole moment: A measure of the charge separation in a molecule: the product of the charge and the distance between the charges: where is the dipole moment, Q is the charge, and r is the separation distance. When there are a number of different charges, it is necessary to sum over all the charges (we will not deal with this case). By convention Q is taken to be the positive charge involved.

Example: If the separation is 1. 00 Å (1 Example: If the separation is 1.00 Å (1.00 x 10-8 cm) and the charge involved is the full electronic charge, calculate the dipole moment.

Example: If the separation is 1. 00 Å (1 Example: If the separation is 1.00 Å (1.00 x 10-8 cm) and the charge involved is the full electronic charge, calculate the dipole moment. The magnitude of the electronic charge is 1.602 x 10-19 C. (The unit of charge in the SI system is the coulomb, abbreviated C).

Example: If the separation is 1. 00 Å (1 Example: If the separation is 1.00 Å (1.00 x 10-8 cm) and the charge involved is the full electronic charge, calculate the dipole moment. The magnitude of the electronic charge is 1.602 x 10-19 C. (The unit of charge in the SI system is the coulomb, abbreviated C).

Example: If the separation is 1. 00 Å (1 Example: If the separation is 1.00 Å (1.00 x 10-8 cm) and the charge involved is the full electronic charge, calculate the dipole moment. The magnitude of the electronic charge is 1.602 x 10-19 C. (The unit of charge in the SI system is the coulomb, abbreviated C). = 1.602 x 10-19 C 1.00 x 10-8 cm = 1.60 x 10-29 Cm

Dipole moments are usually expressed in debye units, abbreviation D: 1 D = 3.336 x 10-30 Cm

The dipole moment in the example is = 1.60 x 10-29 Cm = 4.80 D Dipole moments are usually expressed in debye units, abbreviation D: 1 D = 3.336 x 10-30 Cm The dipole moment in the example is = 1.60 x 10-29 Cm = 4.80 D

The dipole moment in the example is = 1.60 x 10-29 Cm = 4.80 D Dipole moments are usually expressed in debye units, abbreviation D: 1 D = 3.336 x 10-30 Cm The dipole moment in the example is = 1.60 x 10-29 Cm = 4.80 D Note in this example, we have total charge separation (the electron is not shared) so 4.80 D corresponds to an ionic bond.

The dipole moment in the example is = 1.60 x 10-29 Cm = 4.80 D Dipole moments are usually expressed in debye units, abbreviation D: 1 D = 3.336 x 10-30 Cm The dipole moment in the example is = 1.60 x 10-29 Cm = 4.80 D Note in this example, we have total charge separation (the electron is not shared) so 4.80 D corresponds to an ionic bond. Covalently bonded diatomic molecules will have smaller dipole moments (in general).

Key point: In some molecules, the effects of the polar bonds cancel, and even though the individual bonds in the molecule may be polar, the molecule as a whole is nonpolar.

Key point: In some molecules, the effects of the polar bonds cancel, and even though the individual bonds in the molecule may be polar, the molecule as a whole is nonpolar. Example: carbon dioxide, CO2

Key point: In some molecules, the effects of the polar bonds cancel, and even though the individual bonds in the molecule may be polar, the molecule as a whole is nonpolar. Example: carbon dioxide, CO2 O C O

Key point: In some molecules, the effects of the polar bonds cancel, and even though the individual bonds in the molecule may be polar, the molecule as a whole is nonpolar. Example: carbon dioxide, CO2 O C O

Key point: In some molecules, the effects of the polar bonds cancel, and even though the individual bonds in the molecule may be polar, the molecule as a whole is nonpolar. Example: carbon dioxide, CO2 O C O

Key point: In some molecules, the effects of the polar bonds cancel, and even though the individual bonds in the molecule may be polar, the molecule as a whole is nonpolar. Example: carbon dioxide, CO2 O C O Arrows points in the direction of negative charge: these represent the bond dipoles.

The molecular dipole moment is the vector sum of the two bond dipoles The molecular dipole moment is the vector sum of the two bond dipoles. For CO2, this sum = 0.

The molecular dipole moment is the vector sum of the two bond dipoles The molecular dipole moment is the vector sum of the two bond dipoles. For CO2, this sum = 0. So the dipole moment for the molecule is zero, and hence the molecule is nonpolar.

The molecular dipole moment is the vector sum of the two bond dipoles The molecular dipole moment is the vector sum of the two bond dipoles. For CO2, this sum = 0. So the dipole moment for the molecule is zero, and hence the molecule is nonpolar. For this case the bond dipoles have the same magnitude, but they point in opposite directions, and therefore cancel.

Math Aside: Resolving a vector into components.

Math Aside: Resolving a vector into components. Component of in the x direction is

Math Aside: Resolving a vector into components. Component of in the x direction is Component of in the y direction is

Example: BF3, is it polar or nonpolar?

Example: BF3, is it polar or nonpolar Example: BF3, is it polar or nonpolar? To show that the molecule is nonpolar, we would need to prove:

Example: BF3, is it polar or nonpolar Example: BF3, is it polar or nonpolar? To show that the molecule is nonpolar, we would need to prove:

Example: BF3, is it polar or nonpolar Example: BF3, is it polar or nonpolar? To show that the molecule is nonpolar, we would need to prove: That is, the components of the dipole moment of the molecule in the x, y, and z directions must each be zero.

All four atoms are in the x–y plane and the z direction is perpendicular to the plane.

All four atoms are in the x–y plane and the z direction is perpendicular to the plane. Each FBF angle is exactly 120o.

All four atoms are in the x–y plane and the z direction is perpendicular to the plane. Each FBF angle is exactly 120o. There are three bond dipoles, each of strength .

All four atoms are in the x–y plane and the z direction is perpendicular to the plane. Each FBF angle is exactly 120o. There are three bond dipoles, each of strength . The z-direction:

All four atoms are in the x–y plane and the z direction is perpendicular to the plane. Each FBF angle is exactly 120o. There are three bond dipoles, each of strength . The z-direction:

All four atoms are in the x–y plane and the z direction is perpendicular to the plane. Each FBF angle is exactly 120o. There are three bond dipoles, each of strength . The x-direction:

All four atoms are in the x–y plane and the z direction is perpendicular to the plane. Each FBF angle is exactly 120o. There are three bond dipoles, each of strength . The y-direction:

Conclusion: BF3 is a nonpolar molecule.

Example: water.

Example: water. What is the correct shape?

Example: water. What is the correct shape?

Example: water. What is the correct shape?

Example: water (bent shape)