1. Aim: How to describe the polarity of bonds and molecules
Do Now: Draw and label in the image below what the molecule is and what the bond is
bond
molecule

2. Define the following terms in your own words
Bond
Molecule

3. What does polarity mean?
The property of having opposite poles (positive and negative end)
In chemical bonding, polarity has to do with the distribution of charge or electrons in a bond (between two atoms) or in a molecule (group of atoms)

4. Review of electronegativity
Electronegativity is defined as the ability of an atom to attract electrons when the atoms are in a compound.
Explain in terms of electronegativity why Li2O contains an ionic bond, while CO2 has covalent bonds.

5. Are electrons always shared “equally” between two atoms in a covalent bond?
Discuss the question above in pairs. During your discussion think about what the word electronegativity means and consider the electronegativities of the two atoms involved in H-Cl.
Write down what you think.

6. Polar and Nonpolar Bonds
There are two types of covalent bonds
Nonpolar Covalent Bonds (equal share of electrons between two atoms)
Polar Covalent Bonds (unequal share of electrons between two atoms)

7. Polar Covalent Bond
In a polar covalent bond, the shared electrons spend more time around the more electronegative atom
The more electronegative atom has a stronger hold on the shared electrons; has a partial negative charge
The less electronegative atom has weaker hold on the shared electrons; has a partial positive charge

9. How to show a bond is polar
Not a whole charge just a partial charge
d+ means a partially positive (on less electronegative atom)
d- means a partially negative (on more electronegative atom)
Why does chlorine have the partial negative charge?
The Cl pulls harder on the electrons, the electrons spend more time near the Cl d+ d- H Cl

10. Nonpolar Covalent Bond
A Nonpolar Covalent Bond is an equal sharing of electrons between two bonded atoms

11. Classification of Bonds
You can determine the type of bond between two atoms by calculating the difference in electronegativity values between the elements The bigger the electronegativity difference the more polar the bond.
Type of Bond
Electronegativity Difference
Nonpolar Covalent
0  0.4
Polar Covalent
0.5  2.0
Ionic
Greater than 2.0

12. Summary of Polarity of bonds
Non-Polar Covalent Bond
Polar Covalent Bond
Ionic Bond
Between two nonmetal atoms
Between metal ion and nonmetal ion
Equal sharing of electrons
Unequal sharing of electrons
Complete transfer of electrons
EN diff. (0 -0.4)
EN diff. (0.5 – 2.0)
EN diff. greater than 2.0
H-H
H-Cl
𝑁𝑎 𝐶𝑙 −1
No charges on atoms
Partial charges on atoms
Full charges on atoms d+ d-

13. Symmetric vs Asymmetric molecules
Think about what the terms symmetric and asymmetric mean. Next, determine if the following molecules are symmetric or asymmetric.
Asym
Symmetric
Asym
Asym
Symmetric

15. Symmetrical Molecules
In chemistry, symmetry means everything around the central atom is the same (element, shared e- pairs, unshared e- pars)
Symmetric molecules are always nonpolar molecules
There is an even or symmetric distribution of charge throughout the molecule.
Molecule does not exhibit positive and negative ends
Examples:
CO BF3
CCl4

16. Asymmetrical Molecules
In chemistry, asymmetry means that not everything around the central atom is the same (can be shared e-, unshared e-, and/or element)
Asymmetric molecules are polar molecules
There is an uneven or asymmetrical distribution of charge
Molecule exhibits positive and negative end
Examples:
H2O HCl
NH3

17. Water as a Polar Molecule

18. Dipole Polar molecules are also referred to as dipoles
Dipole is a molecule that has two poles or regions with opposite charges

19. Determine which end of the polar molecule (dipole) is the negative end, and which is the positive end.
In a polar molecule, the side of the molecule with the more electronegative atom is the negative end, and the opposite side is the positive end.

20. Practice Dot Structure Bond Type (use EN difference)
Molecule Type (look at molecular shape)
Water H2O
Methane CH4
Carbon Dioxide CO2

21. Answer the following questions
How do you determine if a bond is nonpolar, polar, or ionic?
How do you determine if a molecule is polar or nonpolar?
Why would a molecule with polar bonds not necessarily be a polar molecule? Explain in terms of symmetry.

22. Summary
In a polar bond, one atom is more electronegative than the other.
In a nonpolar bond, both atoms have similar electronegativities.
An asymmetric molecule is a polar molecule.
A symmetric molecule is always a nonpolar molecule.