1CHEMICAL CHEMICAL BONDINGBONDINGw/ Emchw/ Emch

CHEMICAL CHEMICAL BONDINGBONDINGw/ Emchw/ Emch

Cocaine

2Chemical Chemical BondingBonding

Problems and questions —Problems and questions —

How is a molecule or How is a molecule or polyatomic ion held polyatomic ion held together?together?

What’s the difference What’s the difference between ionic, between ionic, covalent, and metallic covalent, and metallic bonds?bonds?

How is bond type related How is bond type related to chemical and to chemical and physical properties?physical properties?

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Review of Chemical BondsReview of Chemical Bonds• There are 3 forms of bonding:There are 3 forms of bonding:• __________________—complete —complete transfer transfer of of 1 or more electrons from one 1 or more electrons from one atom to another (one loses, the atom to another (one loses, the other gains) forming oppositely other gains) forming oppositely charged ions that attract one charged ions that attract one another, producing large another, producing large crystals of ionscrystals of ions

• __________________——some valence some valence electrons electrons sharedshared between atoms… between atoms… forming a moleculeforming a molecule

• __________________ – holds atoms of a – holds atoms of a metal together with “sea of metal together with “sea of electrons”electrons”

Most bonds are Most bonds are somewhere in somewhere in between ionic between ionic and covalent.and covalent.

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Ionic BondsIonic BondsIonic BondsIonic BondsWe’ve been through this in We’ve been through this in great detail already. great detail already. Positive cations and the Positive cations and the negative anions are attracted negative anions are attracted to one another (remember the to one another (remember the Paula Abdul Principle of Paula Abdul Principle of Chemistry: Opposites Chemistry: Opposites Attract!)Attract!)

Therefore, ionic Therefore, ionic compounds are usually compounds are usually between metals and between metals and nonmetals (opposite ends nonmetals (opposite ends of the periodic table).of the periodic table).

5Crystal Structure: Ionic Crystal Structure: Ionic BondingBonding

What are some characteristics of an ionic bond?

1. Crystalline at room temperatures2. Have higher melting points and

boiling points compared to covalent compounds

3. Conduct electrical current in molten or solution state but not in the solid state

4. Polar bonds

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What happens when atoms don’t easily gain/lose

electrons?• Sharing is caring!

• Atoms still want to follow the octet rule

• Covalent bonds are found in all compounds with carbon, all polyatomic ions, and many other compounds

• How can we share electrons? … Time for a demo.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

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Chemical Bonds, Lewis Symbols, and the Octet RuleChemical Bonds, Lewis Symbols, and the Octet Rule

Use Lewis dot diagrams to represent valence Use Lewis dot diagrams to represent valence electrons.electrons.

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Electron Electron Distribution Distribution in Moleculesin Molecules

Electron Electron Distribution Distribution in Moleculesin Molecules

• Electron distribution is Electron distribution is

depicted withdepicted with Lewis Lewis (electron dot) (electron dot) structuresstructures

• 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 (In ionic bonds, it was decided with was decided with charges)charges)

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

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Shared and Lone Shared and Lone PairsPairs

Shared and Lone Shared and Lone PairsPairs

• In a covalent bond, valence In a covalent bond, valence electrons are distributed as electrons are distributed as SHARED (BONDING) PAIRSSHARED (BONDING) 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.

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Bond FormationBond FormationBond FormationBond FormationA covalent bond results from anA covalent bond results from an overlapoverlap of of

atomic orbitals on neighboring atoms with shared atomic orbitals on neighboring atoms with shared pairs of electrons.pairs of electrons. The electrons spend time in The electrons spend time in both atoms.both atoms.

ClH H Cl••

••

••

••

••

••

+

Overlap of H (1s) and Cl (2p)

Note that each atom has a single, Note that each atom has a single, unpaired electron.unpaired electron.

12Review of Valence Review of Valence ElectronsElectrons

Review of Valence Review of Valence ElectronsElectrons

• Remember from the electron Remember from the electron chapter that valence electrons chapter that valence electrons are the electrons in the are the electrons in the OUTERMOST energy level… that’s OUTERMOST energy level… that’s why we did all those electron why we did all those electron configurations!configurations!

• B is 1sB is 1s22 2s 2s22 2p 2p11; so the outer ; so the outer energy level is 2, and there energy level is 2, and there are 2+1 = 3 electrons in level are 2+1 = 3 electrons in level 2. These are the valence 2. These are the valence electrons!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?

13Review of Valence Review of Valence ElectronsElectrons

Review of Valence Review of Valence ElectronsElectrons

Number of valence electrons of a Number of valence electrons of a main (A) group atom = Group numbermain (A) group atom = Group number

Not the transitionNot the transitionmetalsmetals

14Steps for Building a Covalent Steps for Building a Covalent BondBondSteps for Building a Covalent Steps for Building a Covalent BondBond

1.1. Atoms share electrons so that each can Atoms share electrons so that each can “say” they have 8 (octet rule).“say” they have 8 (octet rule).

2.2.Place first atom in center, shared Place first atom in center, shared pairs around the sides.pairs around the sides.

3.3.A Shared pair is converted to a A Shared pair is converted to a LINE. (single bond).LINE. (single bond).

4.4.More than one shared pair is More than one shared pair is converted to more than one line converted to more than one line (DOUBLE OR TRIPLE BOND)(DOUBLE OR TRIPLE BOND)

5.5.You are finished when the octet You are finished when the octet rule is satisfied for each atom, rule is satisfied for each atom, and the total number of electrons and the total number of electrons is correct.is correct.

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Time for Some Examples

• Carbon Tetrachloride

• Ammonia

• Chlorine molecule

• Bromine molecule

• The seven diatomic elements are H, O, N, Cl, Br, I, and F

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

1. Central atom = 1. Central atom =

2. Valence electrons =2. Valence electrons =

3. Form bonds.3. Form bonds.

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

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

5. Check to see that all atoms have 8 electrons 5. Check to see that all atoms have 8 electrons around it except for H, which can have 2.around it except for H, 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 electronsTotal: 16 valence electrons

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

••O OC

•• ••

••••••

••O OC

•• ••

••••••

••O OC

•• ••

••

••O OC

•• ••

••

6. There are too many electrons in our 6. There are too many electrons in our drawing. We must form DOUBLE BONDS between drawing. We must form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a C and O. Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is double bond shares 2 pairs. So one pair is taken away from each atom and replaced with 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?

18Double and Double and even triple even triple bonds are bonds are commonly commonly observed for observed for C, N, P, O, C, N, P, O, and Sand S

••O OC

•• ••

••

••O OC

•• ••

••

HH22COCO

SOSO33

CC22FF44

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Now You Try One!Now You Try One!Draw Sulfur Dioxide, SODraw Sulfur Dioxide, SO22

Now You Try One!Now You Try One!Draw Sulfur Dioxide, SODraw Sulfur Dioxide, SO22

What are some characteristics of a covalent bond?

1. Covalent bonds have definite and predictable shapes.

2. Very strong

3. Low melting and boiling points

4. Flammable (often)

5. Solid, liquid, or gas at room temp

Metallic BondingWhat is a Metallic Bond?

- A metallic bond occurs in metals. A metal consists of positive ions surrounded by a “sea” of mobile electrons.

Name 4 Characteristics of a Metallic Bond.

1. Good conductors of heat and electricity

2. Great strength

3. Malleable and Ductile

4. Luster

This shows what a metallic bond might look like.