1. Chapter 8 Covalent Bonding 8.4 Polar Bonds and Molecules
8.1 Molecular Compounds
8.2 The Nature of Covalent Bonding
8.3 Bonding Theories
8.4 Polar Bonds and Molecules
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2. 8.2 QUIZ
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3. Clear your desks of all except a pencil.
8.2 Lesson Quiz
Clear your desks of all except a pencil.
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4. Please complete worksheet 8.2 Skip the following 7-11, 16, 19-21, 22c
SECTION REVIEW
Please complete worksheet 8.2
Skip the following 7-11, 16, 19-21, 22c
On a separate sheet of paper complete 8.2 lesson Check #20a and b only.
DUE TODAY
PLEASE WORK SILENTLY 
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5. How does a snowflake get its shape?
CHEMISTRY & YOU
How does a snowflake get its shape?
The size and shape of each crystal depends mainly on the air temperature and amount of water vapor in the air at the time the snow crystal forms.
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6. Bond Polarity
Bond Polarity
How do electronegativity values determine the charge distribution in a polar bond?
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7. Bond Polarity
Covalent bonds differ in terms of how the bonded atoms share the electrons.
The character of the molecule depends on the kind and number of atoms joined together.
These features, in turn, determine the molecular properties.
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8. Bond Polarity
The bonding pairs of electrons in covalent bonds are pulled between the nuclei of the atoms sharing the electrons.
The nuclei of atoms pull on the shared electrons, much as the knot in the rope is pulled toward opposing sides in a tug-of-war.
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9. Bond Polarity
The bonding pairs of electrons in covalent bonds are pulled between the nuclei of the atoms sharing the electrons.
When the atoms in the bond pull equally (as occurs when identical atoms are bonded), the bonding electrons are shared equally, and each bond formed is a nonpolar covalent bond.
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10. Bond Polarity
A polar covalent bond, known also as a polar bond, is a covalent bond between atoms in which the electrons are shared unequally.
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11. Bond Polarity
A polar covalent bond, known also as a polar bond, is a covalent bond between atoms in which the electrons are shared unequally.
The more electronegative atom attracts more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge.
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12. Bond Polarity
The higher the electronegativity value, the greater the ability of an atom to attract electrons to itself.
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13. What does the term electronegativity mean?
BELLRINGER
How is the bonding in molecular compounds different from the bonding in ionic compounds?
What does the term electronegativity mean?
Which element is the most electronegative? Which is the least?
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14. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
Hydrogen has an electronegativity of 2.1, and chlorine has an electronegativity of 3.0.
These values are significantly different, so the covalent bond in hydrogen chloride is polar.
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15. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
Hydrogen has an electronegativity of 2.1, and chlorine has an electronegativity of 3.0.
The chlorine atom, with its higher electronegativity, acquires a slightly negative charge.
The hydrogen atom acquires a slightly positive charge.
δ+ δ–
H—Cl
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16. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
The lowercase Greek letter delta (δ) denotes that atoms in the covalent bond acquire only partial charges, less than 1+ or 1–.
δ+ δ–
H—Cl
The minus sign shows that chlorine has a slightly negative charge.
The plus sign shows that hydrogen has acquired a slightly positive charge.
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17. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
These partial charges are shown as clouds of electron density.
This electron-cloud picture of hydrogen chloride shows that the chlorine atom attracts the electron cloud more than the hydrogen atom does.
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18. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
The polar nature of the bond may also be represented by an arrow pointing to the more electronegative atom.
H—Cl
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19. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
The O—H bonds in a water molecule are also polar.
The highly electronegative oxygen partially pulls the bonding electrons away from hydrogen.
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20. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
The O—H bonds in a water molecule are also polar.
The oxygen acquires a slightly negative charge.
The hydrogen is left with a slightly positive charge.
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21. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
The electronegativity difference between two atoms tells you what kind of bond is likely to form.
Electronegativity Differences and Bond Types
Electronegativity difference range
Most probable type of bond
Example
0.0–0.4
Nonpolar covalent
H—H (0.0)
0.4–1.0
Moderately polar covalent
δ+ δ–
H—Cl (0.9)
1.0–2.0
Very polar covalent
H—F (1.9)
>2.0
Ionic
Na+Cl– (2.1)
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22. Describing Polar Covalent Bonds
Bond Polarity
Describing Polar Covalent Bonds
There is no sharp boundary between ionic and covalent bonds.
As the electronegativity difference between two atoms increases, the polarity of the bond increases.
If the difference is more than 2.0, the electrons will likely be pulled away completely by one of the atoms.
In that case, an ionic bond will form.
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23. Sample Problem 8.3
Identifying Bond Type
Which type of bond (nonpolar covalent, moderately polar covalent, very polar covalent, or ionic) will form between each of the following pairs of atoms?
a. N and H
b. F and F
c. Ca and Cl
d. Al and Cl
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24. BELLRINGER
See table 8.4 on page 248 and table 6.2 on page 181 to answer the following:
Which type of bond (nonpolar, very polar covalent, moderately covalent, or ionic) will from between each of the following pairs of ions?
C and H
Be and F
Si and Cl
Nonpolar covalent
ionic
Very polar covalent
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25. Analyze Identify the relevant concepts.
Sample Problem 8.3
Analyze Identify the relevant concepts. 1
In each case, the pairs of atoms involved in the bonding pair are given.
The types of bonds depend on the electronegativity differences between the bonding elements.
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26. Solve Apply concepts to this problem.
Sample Problem 8.3
Solve Apply concepts to this problem. 2
Identify the electronegativities of each atom using Table 6.2.
a. N(3.0), H(2.1)
b. F(4.0), F(4.0)
c. Ca(1.0), Cl(3.0)
d. Al(1.5), Cl(3.0)
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27. Solve Apply concepts to this problem.
Sample Problem 8.3
Solve Apply concepts to this problem. 2
Calculate the electronegativity difference between the two atoms.
The electronegativity difference between two atoms is expressed as the absolute value. So, you will never express the difference as a negative number.
a. N(3.0), H(2.1); 0.9
b. F(4.0), F(4.0); 0.0
c. Ca(1.0), Cl(3.0); 2.0
d. Al(1.5), Cl(3.0); 1.5
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28. Solve Apply concepts to this problem.
Sample Problem 8.3
Solve Apply concepts to this problem. 2
Based on the electronegativity difference, determine the bond type using Table 8.4.
a. N(3.0), H(2.1); 0.9; moderately polar covalent
b. F(4.0), F(4.0); 0.0; nonpolar covalent
c. Ca(1.0), Cl(3.0); 2.0; ionic
d. Al(1.5), Cl(3.0); 1.5; very polar covalent
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29. Describing Polar Covalent Molecules
Bond Polarity
Describing Polar Covalent Molecules
The presence of a polar bond in a molecule often makes the entire molecule polar.
In a polar molecule, one end of the molecule is slightly negative, and the other end is slightly positive.
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30. INDEPENDENT ASSIGNMENT
In your notes notebook: Add the info from table 6.2 pg. 181 to your periodic table and copy table 8.4 pg. 248 to your notes.
ON A SEPARATE SHEET OF PAPER (Q+A)
PLEASE COMPLETE #’S FROM PAGE 249
DUE AT 10:00AM.
PLEASE RAISE YOUR HAND FOR HELP
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31. Describing Polar Covalent Molecules
Bond Polarity
Describing Polar Covalent Molecules
In the hydrogen chloride molecule, for example, the partial charges on the hydrogen and chlorine atoms are electrically charged regions, or poles.
A molecule that has two poles is called a dipolar molecule, or dipole.
The hydrogen chloride molecule is a dipole.
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32. Describing Polar Covalent Molecules
Bond Polarity
Describing Polar Covalent Molecules
When polar molecules are placed between oppositely charged plates, they tend to become
oriented with
respect to the
positive and
negative
plates.
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33. Describing Polar Covalent Molecules
Bond Polarity
Describing Polar Covalent Molecules
The effect of polar bonds on the polarity of an entire molecule depends on the shape of the molecule and the orientation of the polar bonds.
A carbon dioxide molecule has two polar bonds and is linear.
O C O
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34. Describing Polar Covalent Molecules
Bond Polarity
Describing Polar Covalent Molecules
The water molecule also has two polar bonds.
However, the water molecule is bent rather than linear.
Therefore, the bond polarities do not cancel and a water molecule is polar.
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35. What is the difference between an ionic bond and a very polar covalent bond?
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36. What is the difference between an ionic bond and a very polar covalent bond?
Two atoms will form an ionic bond rather than a very polar covalent bond if the two atoms have a slightly higher difference in electronegativity—a difference of more than 2.0. There is no sharp boundary between ionic and covalent bonds.
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37. Attractions Between Molecules
How do the strengths of intermolecular attractions compare with ionic and covalent bonds?
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38. Attractions Between Molecules
Molecules can be attracted to each other by a variety of different forces.
Intermolecular attractions are weaker than either ionic or covalent bonds.
Among other things, these attractions are responsible for determining whether a molecular compound is a gas, a liquid, or a solid at a given temperature.
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39. Attractions Between Molecules
Van der Waals Forces
The two weakest attractions between molecules are collectively called van der Waals forces, named after the Dutch chemist Johannes van der Waals.
Van der Waals forces consist of dipole interactions and dispersion forces.
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40. Attractions Between Molecules
Van der Waals Forces
Dipole interactions occur when polar molecules are attracted to one another.
The electrical attraction occurs between the oppositely charged regions of polar molecules.
Dipole interactions are similar to, but much weaker than, ionic bonds.
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41. Attractions Between Molecules
Van der Waals Forces
The slightly negative region of a polar molecule is weakly attracted to the slightly positive region of another polar molecule.
Dipole interactions are similar to, but much weaker than, ionic bonds.
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42. Attractions Between Molecules
Van der Waals Forces
Dispersion forces, the weakest of all molecular interactions, are caused by the motion of electrons.
They occur even between nonpolar molecules.
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43. Attractions Between Molecules
Van der Waals Forces
Dispersion forces, the weakest of all molecular interactions, are caused by the motion of electrons.
When the moving electrons happen to be momentarily more on the side of a molecule closest to a neighboring molecule, their electric force influences the neighboring molecule’s electrons to be momentarily more on the opposite side.
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44. Attractions Between Molecules
Van der Waals Forces
Dispersion forces, the weakest of all molecular interactions, are caused by the motion of electrons.
The strength of dispersion forces generally increases as the number of electrons in a molecule increases.
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45. Attractions Between Molecules
Van der Waals Forces
Fluorine and chlorine have relatively few electrons and are gases at ordinary room temperature and pressure because of their especially weak dispersion forces.
Bromine molecules therefore attract each other sufficiently to make bromine a liquid under ordinary room temperature and pressure.
Iodine, with a still larger number of electrons, is a solid at ordinary room temperature and pressure.
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46. Attractions Between Molecules
Hydrogen Bonds
The dipole interactions in water produce an attraction between water molecules.
Each O—H bond in the water molecule is highly polar, and the oxygen acquires a slightly negative charge because of its greater electronegativity.
The hydrogens in water molecules acquire a slightly positive charge.
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47. Attractions Between Molecules
Hydrogen Bonds
The positive region of one water molecule attracts the negative region of another water molecule.
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48. Attractions Between Molecules
Hydrogen Bonds
This relatively strong attraction, which is also found in hydrogen-containing molecules other than water, is called a hydrogen bond.
Hydrogen bond
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49. Attractions Between Molecules
Hydrogen Bonds
Hydrogen bonds are attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom.
The other atom may be in the same molecule or in a nearby molecule.
Hydrogen bonding always involves hydrogen.
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50. Attractions Between Molecules
Hydrogen Bonds
A hydrogen bond has about 5 percent of the strength of the average covalent bond.
Hydrogen bonds are the strongest of the intermolecular forces.
They are extremely important in determining the properties of water and biological molecules.
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51. How does a snowflake get its shape?
CHEMISTRY & YOU
How does a snowflake get its shape?
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52. How does a snowflake get its shape?
CHEMISTRY & YOU
How does a snowflake get its shape?
A snowflake’s shape is determined by the interactions of hydrogen bonds during its formation.
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53. Why are hydrogen bonds important?
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54. Why are hydrogen bonds important?
Hydrogen bonds are the strongest of the intermolecular forces and are extremely important in determining the properties of water and biological molecules such as proteins.
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55. Worksheet 8.4 Due Today It’s a classwork grade!!!!
Don’t do #’s 13 or 20.
Study for your test. See homework page and pearson website for more info.
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56. Chapter 8 Test
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57. Key Concepts
When different atoms bond, the more electronegative atom attracts electrons more strongly and acquires a slightly negative charge.
Intermolecular attractions are weaker than either an ionic or a covalent bond.
The diversity of physical properties among covalent compounds is mainly because of widely varying intermolecular attractions.
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58. Glossary Terms
nonpolar covalent bond: a covalent bond in which the electrons are shared equally by the two atoms
polar covalent bond (polar bond): a covalent bond between atoms in which the electrons are shared unequally
polar molecule: a molecule in which one side of the molecule is slightly negative and the opposite side is slightly positive
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59. Glossary Terms
dipole: a molecule that has two poles, or regions with opposite charges
van der Waals forces: the two weakest intermolecular attractions—dispersion interactions and dipole forces
dipole interactions: intermolecular forces resulting from the attraction of oppositely charged regions of polar molecules
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60. Glossary Terms
dispersion forces: attractions between molecules caused by the electron motion on one molecule affecting the electron motion on the other through electrical forces; these are the weakest interactions between molecules
hydrogen bonds: attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom
network solid: a solid in which all of the atoms are covalently bonded to each other
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61. END OF 8.4
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