Understanding Covalent Compounds: Lewis Electron Dot Structures and Molecular Shapes, Slides of Chemistry

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COVALENT COMPOUNDS

• Covalent Compounds
• Formed when two

elements, usually 2

nonmetals, SHARE

electrons.

• Ionic Compounds
• Formed when two

elements, usually a

metal and a nonmetal,

TRANSFER electrons.

Electronegativity

http://www.meta-synthesis.com/webbook/30_timeline/pauling.jpg

• Electronegativity is the ability of an atom to attract a pair of electrons in a chemical bond.
• An electronegativity difference greater than 1.7 is usually considered to be a ionic bond.
• Less than 1.7 but greater than 0 is POLAR COVALENT. Electrons are shared but not equally.
• Equal to zero is NONPOLAR COVALENT. Electrons are EQUALLY SHARED BETWEEN THE 2 ATOMS.
• lithium and fluorine
• oxygen and chlorine
• nitrogen and nitrogen

Lewis Electron Dot Practice

• water (H

2

O)

• sodium chloride (NaCl)

• aluminum oxide (Al

2

O

3

• ammonia (NH

3

• methane (CH

4

• carbon dioxide (CO

2

• phosphorus pentachloride (PCl

5

• sulfur hexafluoride (SF

6

Molecular Shapes

• The shapes of molecules determine many of their chemical and physical properties.
• VSEPR: valance shell electron pair repulsion.
• This model minimizes the repulsion of shared and unshared electrons.

Covalent Molecules

• Date:

• Partners:

• Problem: How can the Lewis Electron Dot

Model and VSEPR be used to determine the

shape and polarity of covalent molecules?

• Hypothesis:

Procedures

• Materials: Molecular Model Kits
• black = carbon; red = oxygen; blue = nitrogen; white = hydrogen; green = chlorine; orange = bromine; purple = iodine; gray = phosphorus; yellow = sulfur;
• stick = single bond; spring = multiple bond
• Procedures:
• Assemble the model for each of the molecules listed.
• Draw the electron dot diagram for each molecule.
• Calculate the electronegativity difference to determine the type of bond.
• Determine the shape of the molecule.
• Determine the type of molecule.

Conclusion

• Conclusion:
• Theoretical Discussion:
• Research VSEPR.
• Questions:
• 1. Do all molecules that have polar bonds make polar molecule? Explain by giving examples.
• 2. Both water and carbon dioxide are triatomic molecules. Explain why water is polar and carbon dioxide is nonpolar.