•EXAM #3 Correction- Check OWL•Chapter 8

•Homework posted•Today’s Topic: Lewis Structures (Sec. 8.2)

Bond Properties (Sec. 8.3)

November 11, 2009

Why does a covalent bond form?

1. The valence electrons on two atoms are attracted to one another

2. The nuclei of two atoms are attracted to one another

3. The valence electrons on one atom are attracted to the nucleus of another atom

4. The repulsive forces between the protons in two nuclei and between the electrons in two atoms are strong

Last time…

Bonds form when the balance of forces favors bond formation

Valence electrons are those in the outermost shell (highest n-level)

Lewis structures are used to show the valence electrons Elemental symbol = core (nucleus + inner electrons) Lines = bonding electrons Dots = electrons not involved in a bond

Rules for Drawing Lewis Structures

1. Write the skeletal structure2. Add up the total # of valence electrons3. Draw a bond between the central atom and each

surrounding atom4. Add lone pairs to the outer atoms to complete their

octets5. Add remaining electrons to central atom6. If central atom does not have an octet, “borrow”

electrons from other atoms (make double/triple bonds)- DO NOT ADD ELECTRONS (F and Cl do not form multiple bonds; C, N, O, P, and S do)

7. Sometimes you can’t complete an octet (B and Be)

How many total bonding electrons does an acetate ion have?

1. 72. 83. 104. 125. 136. 147. 15

Examples

Try this one at home!

Draw the Lewis structure for SO3. How many lone pairs does it have?

1. 22. 43. 64. 85. 10

What does the Lewis Structure for N2 look like?

:: NN

:: NN

:: NN

::

NN

1.

2.

3.

4.

Exceptions to the Octet Rule

H (2)Be (4)B (6)Large elements with available d orbital

Organic Structures

CH3CH3

CH3CN

CHCCHCH2