U6L5 - Lecture Notes - Electronegativity and Polarity

​U6L5
Electronegativity and
Polarity

Essential Questions

• How is electronegativity used to determine bond type?

• How do polar and nonpolar covalent bonds and polar and nonpolar
molecules compare and contrast?

• What are the characteristics of covalently bonded compounds?

Electronegativity and Polarity
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Electronegativity and Bond Character

• Electron affinity measures the tendency of an atom to accept an electron.

• Noble gases are not listed because they generally do not form compounds.

Electronegativity and Polarity
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• The relative ability of an atom to attract electrons in a chemical bond is called
electronegativity.

Multiple Choice

Partial charges are present in which type of bond?

• Ionic

• Nonpolar Covalent

• Polar Covalent

• Both Polar Covalent and Ionic

Electronegativity and Bond Character

• This table lists the character and type of chemical bond that forms with
differences in electronegativity.

Electronegativity and Polarity
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Electronegativity and Bond Character

• Unequal sharing of electrons results in a polar covalent bond.

• Bonding is often not clearly ionic or covalent.

• This graph summarizes the range of chemical bonds between two atoms.

Electronegativity and Polarity
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•​ The polarity of a bond is determined by the difference in the electronegativities of the two atoms.

Multiple Choice

Unequal sharing of electrons results in which of the following?

• polar covalent bond

• non polar covalent bond

• ionic bond

Multiple Choice

Order the types of bonds based on the charge of their molecules. (lowest amount of charge to greatest)

• Polar Covalent --> Ionic --> Nonpolar Covalent

• Ionic --> Nonpolar Covalent --> Polar Covalent

• Ionic --> Polar Covalent --> Nonpolar Covalent

• Nonpolar Covalent --> Polar Covalent --> Ionic

Polar Covalent Bonds

• Polar covalent bonds form when atoms pull on electrons in a molecule unequally.

• Electrons spend more time around one atom than another resulting in partial
charges at the ends of the bond called a dipole.

Electronegativity and Polarity
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​• In a polar covalent bond, the electrons gather around the atom with the Greatest Electronegativity.

Multiple Choice

The polarity of a bond is determined by...

• The sum of the electronegativities of the two atoms

• The difference in the electronegativities of the two atoms

• The charges of the atoms

• None of the Above

Multiple Choice

In a polar covalent bond, the electrons gather around...

• The atom with the Greatest Electronegativity

• The atom with the Lowest Electronegativity

• Each atom Equally

• None of the Above

Polar Covalent Bonds

• Covalently bonded molecules are either polar or non-polar.

• Non-polar molecules are not attracted by an electric field.

• Polar molecules align with an electric field.

• Compare water, H2O, and CCl4.

–Both bonds are polar.

–The molecular shapes, determined by VSEPR, is bent and tetrahedral, respectively.

–O – H bonds are asymmetric in water, so has a definite positive end and
definite negative end. Thus, polar. The C – Cl bonds are symmetrical in CCl4.
The electric charge measured at any distance from the center is identical on all sides and partial charges are balanced. Thus nonpolar.

Electronegativity and Polarity
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Polar Covalent Bonds

• Note: If bonds are polar, asymmetrical molecules are polar and symmetrical molecules are nonpolar.

Electronegativity and Polarity
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Multiple Choice

True or False: If bonds are polar, asymmetrical molecules are polar and symmetrical molecules are nonpolar.

• True

• False

Polar Covalent Bonds

• Solubility is the property of a substance’s ability to dissolve in another substance.

• Polar molecules and ionic substances are usually soluble in polar substances.

• Non-polar molecules dissolve only in non-polar substances.

Electronegativity and Polarity
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Properties of Covalent Compounds

• Covalent bonds between atoms are strong, but attraction forces between
molecules are weak.

• The weak attraction forces are known as van der Waals forces.

• The forces vary in strength but are weaker than the bonds in a molecule or
ions in an ionic compound.

• Non-polar molecules exhibit a weak dispersion force, or induced dipole.

• The force between two oppositely charged ends of two polar molecules is a dipole-dipole force.

• A hydrogen bond is an especially strong dipole-dipole force between a
hydrogen end of one dipole and a fluorine, oxygen, or nitrogen atom on
another dipole.

Electronegativity and Polarity
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Multiple Choice

What type of molecules exhibit a weak dispersion force, or induced dipole?

• Polar

• Non-polar

• Ionic

Properties of Covalent Compounds

• Many physical properties are due to intermolecular forces.

• Weak forces result in the relatively low melting and boiling points of
molecular substances.

• Many covalent molecules are relatively soft solids.

• Molecules can align in a crystal lattice, similar to ionic solids but with less
attraction between particles.

• Solids composed of only atoms interconnected by a network of covalent
bonds are called covalent network solids.

• Quartz and diamonds are two common examples of network solids.

Electronegativity and Polarity
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