NOTES: LEWIS DOT STRUCTURES

ChemistryBoonDate: 09/06 & 09/07 2012

CatalystIonic or Covalent? Hint: Ionic bonds form

between a metal and a nonmetal. Covalent bonds form between two or more nonmetals.

1. NaCl2. MgF2

3. O2

4. H2

5. CO2

6. CH4

7. Ag2O

Objectives I can explain the difference between

ionic and covalent compounds and bonds.

I can draw simple Lewis structures of molecules.

Agenda

Catalyst HW Review Open Note Quiz Lewis Dot Structures of Molecules

HW Review: p. 184 #23Atom Ion Noble-gas configuration of ion

S – sulfur (6 v.e.) S2- Argon – 1s2 2s2 2p6 3s2 3p6

Be – Beryllium (2 v.e.)

Be2+ Helium – 1s2

I – Iodine (7 v.e.) I- Xenon - 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6

Rb – Rubidium (1 v.e.)

Rb+ Krypton - 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

O – oxygen (6 v.e) O2- Neon - 1s2 2s2 2p6

Sr – Strontium (2 v.e.)

Sr2+ Krypton - 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6

F – Fluorine (7 v.e.) F- Neon - 1s2 2s2 2p6

Hint: Octet Rule: Metals lose all their negatively charged valence electrons to form positive cations. Nonmetals gain enough electrons to have a full outer shell (usually to end up with 8) and form negative anions.• These ions end up with the same number of electrons as the noble gas

closest to them on the periodic table.

HW Review (p. 198 & 216) 7. Molecular compounds have low melting points

and low boiling point relative to ionic substances because the atoms in a covalent compound have a strong attraction to the atoms that they share electrons with, but there is little attraction for the atoms of other nearby molecules.

10. How does the strength of a covalent bond relate to bond length?

Generally, as the bond length gets shorter, the strength of the covalent bond gets stronger.

11. How does a covalent bond differ from an ionic bond?

In an ionic bond, electrons are transferred from a metal to a nonmetal. Covalent bonds usually form between nonmetals and involve the sharing of electrons.

HW Review Continued Nonpolar = electrons are shared equally

Atoms have similar electronegativities – so they pull on the electrons equally

Polar = electrons are not shared equally Atoms have different electronegativities – so they pull

on the electrons unequally

15. Ionic/Nonpolar covalent/polar covalent? a. Na-F: ionic b. H-I: polar covalent c. N-O: nonpolar covalent d. Al-O: ionic or polar covalent e. S-O: polar covalent f. H-H: nonpolar covalent

Open Note Quiz1. What ionic compound do Ca and Br form?

Write the formula Write the name in words

2. WRITE A PARAGRAPH USING THIS FORMAT:

Ionic compounds and covalent compounds are similar because they both (write at least 3 similarities here)

Ionic compounds and covalent compounds are different because

Ionic compounds _______________, but covalent compounds ____________________. (repeat for at least 3 differences)

Agenda

Catalyst HW Review Open Note Quiz Lewis Dot Structures of Molecules

Lewis Dot Structures

Lewis Dot Structures show how valence electrons are arranged in atoms and molecules

Lewis dot structures for single atoms 1e- 2e- 3e- 4e-

5e- 6e- 7e- 8e-

Na Mg Al C

N O F Ne

Rules for covalent bonding Each bond is made up of 2 electrons

Each atom wants to reach the same configuration as the noble gases Duet rule: Hydrogen wants 2 valence electrons Octet rule: All other atoms want 8 valence

electrons

Atoms will share electrons with other atoms so that both get a full valence shell

Drawing Lewis Dots for Compounds

Steps: 1. Draw Lewis Dot structures for

the individual atoms Double check your numbers of

valence e- 2. Put central atom in the center 3. Put other atoms around 4. Draw 2 dots between each pair 5. Fill in other dots up to 8 (except

for H) 6. Replace all bonded pairs with

lines

CH4

Central atom

C

H

H

H H

Practice Lewis Dots

NH3

H2O

H HHN

Total electrons:NH3

H3 = 3 x 1 = 3N = 5

8

Practice!

CF4

HCl

CH2Br2

C2H6

NOTES: LEWIS DOT STRUCTURES PART 2

ChemistryDate: 09/06 & 09/07 2012

Double and Triple Bonds

What happens when the total electrons do not match up with the Lewis structure?

Example:O2

Draw the Lewis dot structure:

O OTotal valence electrons:

O2 = 2 x 6 = 12

Single bonded structure uses too many electrons!

Double Bonds

If the structure has too many dots, remove lone pairs from two atoms and replace with a double bond

In a double bond, the atoms share 4 electrons

Replace the bonded pairs with 2 lines

O OLone pairs

Double Bonds

Some atoms can have more than one double bond

Example: CO2

Total valence electrons:

O2 = 2 x 6 = 12C = 4

16C OO