Chapter 4, Section 2Covalent Bonds

Monday, December 14, 2009

Pages 121 -- 125

Objectives

• Describe how covalent bonds form.

• Identify the properties of molecular compounds.

• Distinguish between polar and nonpolar bonds, and between polar and nonpolar compounds.

Vocabulary Words

• Covalent bond

• Double bond

• Molecular compound

• Polar

• Nonpolar

Covalent Bond

• A covalent bond results from a chemical bond that is formed when two atoms share electrons.

• Covalent bonds form between two or more nonmetals.

• In a covalent bond, both atoms attract the two shared electrons at the same time.

How Many Bonds?

• The number of bonds an atom can form equals the number of valence electrons needed to make a total of eight.

• If two pairs of electrons are shared, it forms a double bond.

• If three pairs of electrons are shared, it forms a triple bond.• The shared pairs count for both atoms forming a

bond.

Molecular Compound

• Molecular compound consists of molecules having covalently bonded atoms.• These compounds have different properties from

ionic compounds.• Most molecular compounds are poor conductors

of electricity.• No charged particles are available to move.

• Molecular compounds have low melting and boiling points.

Unequal Sharing of Electrons

• Some atoms pull more strongly on the shared electrons than other atoms do.• The electrons move closer to one atom.• The atom now has a slight electrical

charge.

Polar

• A covalent bond in which electrons are shared unequally is polar.

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Nonpolar Bond

• The valence electrons are shared equally and the bond is nonpolar.

• A molecule is nonpolar if it contains polar bonds that cancel each other.

• Molecules that contain only nonpolar bonds are also nonpolar.

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Attraction Between Molecules

• Differences in the attraction between molecules lead to different properties in polar and nonpolar compounds.• Example: Oil and water.

• Oil is nonpolar and water is polar.

Homework

• Workbook 4.2 (due 12/16)

• No vocabulary quiz!