Bonding UnitLearning Goal #1: Analyze the relationship between the valence (outermost) electrons of an atom and the type of bond formed between atoms.

Electronse-

Negative Charge

Mass = 1/2000 amu

Found in the Electron ShellArranged in Energy Levels

In a neutral atom the electrons equal the protons.

Electrons are gained or lost in the formation of an ion.

Electron Shells (Energy Levels)

Review of Valence ElectronsReview of Valence ElectronsReview of Valence ElectronsReview of Valence Electrons• RememberRemember::

– Valence electrons are the Valence electrons are the electrons in the OUTERMOST electrons in the OUTERMOST energy level… that’s why we did energy level… that’s why we did all those electron configurations!all those electron configurations!

• B is 1sB is 1s22 2s 2s22 2p 2p11 The outer energy level is 2The outer energy level is 2

2+1 = 3 electrons 2+1 = 3 electrons These are the valence electrons!These are the valence electrons!

• Br is Br is [Ar] 4s[Ar] 4s22 3d 3d1010 4p 4p55

How many valence electrons are How many valence electrons are present?present?

Electron Electron Distribution Distribution

in in MoleculesMolecules

Electron Electron Distribution Distribution

in in MoleculesMolecules

• Valence Electron Valence Electron distribution is depicted distribution is depicted withwith Lewis (electron Lewis (electron dot) structuresdot) structures

• This is how you This is how you decide how many decide how many atoms will bond atoms will bond covalently! covalently! (In ionic bonds, it was (In ionic bonds, it was decided with decided with charges)charges)

G. N. Lewis G. N. Lewis 1875 - 19461875 - 1946

Practice

Bond FormationBond FormationBond FormationBond FormationA bond can result from anA bond can result from an

Interaction between valence electrons.Interaction between valence electrons.

Chemical bonds: an attempt to fill electron

shells1. Ionic bonds 2. Covalent bonds 3. Metallic bonds

Hydrogen and Helium follow the duet rule. They fill the outer electron shell with TWO electrons.

8 Electrons

Violations of the Octet RuleViolations of the Octet RuleViolations of the Octet RuleViolations of the Octet Rule

Usually occurs with B and Usually occurs with B and elements of higher periods. elements of higher periods. Common exceptions are: Be, B, Common exceptions are: Be, B, P, S, and Xe. P, S, and Xe.

BF3BF3

SF4SF4

Be: 4Be: 4

B: 6B: 6

P: 8 OR 10P: 8 OR 10

S: 8, 10, OR 12S: 8, 10, OR 12

Xe: 8, 10, OR 12Xe: 8, 10, OR 12

IONIC BONDBond formed between

two ions by the transfer of electrons

Metal + Nonmetal

Ionic compounds result when metals react with nonmetals

Metals lose electrons to match the number of valence electrons of their nearest noble gas

Positive ions form when the number of electrons are less than the number of protons

Group 1 metals ion 1+

Group 2 metals ion 2+

• Group 13 metals ion 3+

In ionic compounds, nonmetals in 15, 16,

and 17 gain electrons from metals

Nonmetal add electrons to achieve the

octet arrangement

Nonmetal ionic charge:

3-, 2-, or 1-

COVALENT BONDBond formed by the sharing of electrons

Nonmetal + Nonmetal

14, 15, 16, 17 AndHydrogen

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.

Oxygen AtomOxygen Atom Oxygen AtomOxygen Atom

Oxygen Molecule (O2)

Bonds in all the polyatomic ions

and diatomics are all covalent bonds

METALLIC BONDBond found in metals; holds metal atoms together very strongly Metal + Metal Electrons

move freely around the positive nuclei of the metal atoms.

Bond and Lone Bond and Lone PairsPairs

Bond and Lone Bond and Lone PairsPairs• Valence electrons are distributed Valence electrons are distributed

as shared oras shared or BOND PAIRSBOND PAIRS and and unshared orunshared or LONE PAIRS.LONE PAIRS.

•

••

•

••

H Cllone pair (LP)

shared orbond pair

This is called a This is called a LEWIS LEWIS structure.structure.

Steps for Building a Dot StructureSteps for Building a Dot StructureSteps for Building a Dot StructureSteps for Building a Dot StructureAmmonia, NHAmmonia, NH33

1.1.Decide on the central atom; never H. Decide on the central atom; never H. Therefore, N is central on this oneTherefore, N is central on this one

2. 2. Add up the number of valence electrons Add up the number of valence electrons that can be used.that can be used.

H = 1 and N = 5H = 1 and N = 5

Total = (3 x 1) + 5 Total = (3 x 1) + 5

= 8 electrons / 4 pairs= 8 electrons / 4 pairs

3.3. Form a single bond between the Form a single bond between the central atom and each surrounding central atom and each surrounding atom (each bond takes 2 electrons!)atom (each bond takes 2 electrons!)

H H

H

N

Building a Dot StructureBuilding a Dot Structure

H••

H

H

N4.Remaining electrons form LONE 4.Remaining electrons form LONE PAIRS to complete the octet as needed PAIRS to complete the octet as needed (or duet in the case of H).(or duet in the case of H).

3 BOND PAIRS and 1 LONE PAIR.3 BOND PAIRS and 1 LONE PAIR.

Note that N has a share in 3 pairs (6 electrons), while Note that N has a share in 3 pairs (6 electrons), while H shares 1 pair (2 electrons).H shares 1 pair (2 electrons).

5.5. Check to make sure there are 8 Check to make sure there are 8 electrons around each atom except H. electrons around each atom except H. H should only have 2 electrons. This H should only have 2 electrons. This includes SHARED pairs. includes SHARED pairs.

Building a Dot StructureBuilding a Dot Structure

6. 6. Also, check the number of electrons in your Also, check the number of electrons in your drawing with the number of electrons from drawing with the number of electrons from step 2. step 2. If you have more electrons in the If you have more electrons in the drawing than in step 2, you must make drawing than in step 2, you must make double or triple bonds. If you have less double or triple bonds. If you have less electrons in the drawing than in step 2, you electrons in the drawing than in step 2, you made a mistake!made a mistake!

H••

H

H

N

Carbon Dioxide, COCarbon Dioxide, CO22Carbon Dioxide, COCarbon Dioxide, CO22

1.1. Central atom = Central atom =

2. Valence electrons =2. Valence electrons =

3. Form bonds.3. Form bonds.

O OC4. Place lone pairs on outer atoms.4. Place lone pairs on outer atoms.

This leaves 12 electrons (6 pair).This leaves 12 electrons (6 pair).

5. Check to see that all atoms have 8 electrons around it except for H, 5. Check to see that all atoms have 8 electrons around it except for H, which can have 2.which can have 2.

C 4 e-C 4 e-O 6 e- X 2 O’s = 12 e-O 6 e- X 2 O’s = 12 e-Total: 16 valence Total: 16 valence electronselectrons

Carbon Dioxide, COCarbon Dioxide, CO22Carbon Dioxide, COCarbon Dioxide, CO22

••O OC

•• ••

••••••

••O OC

•• ••

••••••

••O OC

•• ••

••

••O OC

•• ••

••

66. There are too many electrons in our drawing. We must . There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O. Instead of form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a double bond shares 2 pairs. So one sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from each atom and replaced with pair is taken away from each atom and replaced with another bond.another bond.

C 4 e-C 4 e-O 6 e- X 2 O’s = 12 e-O 6 e- X 2 O’s = 12 e-Total: 16 valence electronsTotal: 16 valence electrons

How many are in the drawing?How many are in the drawing?

Practice Problems

Resonance StructureA resonance structure is an alternate way of drawing a Lewis dot structure for a compound. For some molecules, there are multiple ways to draw a Lewis dot structure that still satisfy the rules

Essential Questions

1.How can a pattern in the periodic table be used to describe an element’s number of valence electrons?

2.Describe how the number of valence electrons can be used to predict the loss or gain of the electrons and the subsequent charge on the resulting ion.