Covalent BondsCovalent Bonds

Part 2Part 2

When two atoms have a covalent When two atoms have a covalent bond, the valence orbital of one atom bond, the valence orbital of one atom overlaps or merges with the valence overlaps or merges with the valence orbital of another atomorbital of another atom

Bonding orbitalBonding orbital• localized region where bonding localized region where bonding

electrons can most likely be foundelectrons can most likely be found

• Single covalent bonds (one bonding pair)Single covalent bonds (one bonding pair)• Occurs when electron pair is shared in Occurs when electron pair is shared in

area centered between two atomsarea centered between two atoms• Results if atomic orbitals overlap end to Results if atomic orbitals overlap end to

endend• Sigma bonds form with:Sigma bonds form with:

Overlap of s-orbital and s-orbitalOverlap of s-orbital and s-orbital Overlap of s-orbital and p-orbitalOverlap of s-orbital and p-orbital Overlap of p-orbital and p-orbital Overlap of p-orbital and p-orbital

Sigma bonds (Sigma bonds (σσ))

Multiple BondsMultiple Bonds

Double BondDouble Bond• Two bonding pairs of electronsTwo bonding pairs of electrons• Consist of a sigma bond and one pi bondConsist of a sigma bond and one pi bond

Triple BondTriple Bond• Three bonding pairs of electrons Three bonding pairs of electrons • Consist of a sigma bond and 2\two pi Consist of a sigma bond and 2\two pi

bondsbonds

Pi bonds (Pi bonds (∏∏))

Formed when parallel orbitals Formed when parallel orbitals overlap to share electronsoverlap to share electrons

Electrons shared in a pi bond occupy Electrons shared in a pi bond occupy the space above and below the line the space above and below the line that represents where the two atoms that represents where the two atoms are joined togetherare joined together

Double and triple bonds consist of a Double and triple bonds consist of a sigma bond and one or two pi bondssigma bond and one or two pi bonds

Bond StrengthBond Strength

Recap: How are covalent bonds Recap: How are covalent bonds formedformed

Attractive and repulsive forcesAttractive and repulsive forces Covalent bond broken when balance Covalent bond broken when balance

upsetupset Bond strength determined by Bond strength determined by

different factorsdifferent factors

Bond lengthBond length

The distance from the center of one The distance from the center of one nucleus to the center of the other nucleus to the center of the other nucleus of two bonded atoms during nucleus of two bonded atoms during the the point of maximum attractionpoint of maximum attraction

Determined by:Determined by:• Size of atomSize of atom• Number of electrons sharedNumber of electrons shared

Shared Pairs…Shared Pairs…

INCREASE the number of shared INCREASE the number of shared pairs of electrons pairs of electrons DECREASE bond DECREASE bond lengthlength

Triple bond has shorter bond length Triple bond has shorter bond length than single bond lengththan single bond length

Single bonds are weaker than double Single bonds are weaker than double bonds, which are weaker than triple bonds, which are weaker than triple bondsbonds

Energy in BondsEnergy in Bonds

When bond is formedWhen bond is formed E released E released When bond is brokenWhen bond is broken E is required E is required Bond Dissociation EnergyBond Dissociation Energy

• Amount of energy required to break a Amount of energy required to break a specific covalent bondspecific covalent bond

• Breaking bonds requires adding energyBreaking bonds requires adding energy• Positive value kJ/molPositive value kJ/mol• Sum of bond dissociation energies for all Sum of bond dissociation energies for all

bonds in a compound determines the bonds in a compound determines the chemical potential energy available in a chemical potential energy available in a molecule of that compoundmolecule of that compound

Relationship Between Bond Energy Relationship Between Bond Energy and Bond Lengthand Bond Length

The closer atoms are bonded The closer atoms are bonded together, the more energy is together, the more energy is required to break the bondrequired to break the bond

DECREASE bond length = INCREASE DECREASE bond length = INCREASE bond dissociation energybond dissociation energy

Which of the following has the Which of the following has the greatest bond energy? Which has the greatest bond energy? Which has the least?least?• FF22, O, O22, N, N22

Total Energy change of chemical Total Energy change of chemical reaction determined by the energy of reaction determined by the energy of bonds broken and formedbonds broken and formed

Endothermic ReactionsEndothermic Reactions• Greater amount of energy required to Greater amount of energy required to

break the existing bonds in the break the existing bonds in the reactants than is produced in the new reactants than is produced in the new bonds formed in the productsbonds formed in the products

Exothermic ReactionsExothermic Reactions• More energy is released forming new More energy is released forming new

bonds in the products than is required to bonds in the products than is required to break the bonds in the initial reactants break the bonds in the initial reactants

Naming MoleculesNaming Molecules

Binary molecular compoundBinary molecular compound• Covalently bonded compound Covalently bonded compound

containing only two different elementscontaining only two different elements• Composed of 2 different nonmetalsComposed of 2 different nonmetals

No ions or metalsNo ions or metals

Naming Binary Molecular CompoundsNaming Binary Molecular Compounds The first element in the formula is always The first element in the formula is always

named first, using the entire element named first, using the entire element namename

The second element in the formula is The second element in the formula is named using the root of the element and named using the root of the element and adding the suffix –adding the suffix –ideide

Prefixes are used to indicate the number Prefixes are used to indicate the number of atoms of each type that are present in of atoms of each type that are present in the compoundthe compound• Exception: first element in formula never uses Exception: first element in formula never uses

monomono-- Drop final letter in the prefix when the Drop final letter in the prefix when the

element name begins with a vowelelement name begins with a vowel Hydrogen bonded to 7A halogens (drop Hydrogen bonded to 7A halogens (drop

mono)mono)

1 - mon(o) 1 - mon(o) 2 - di 2 - di 3 - tri 3 - tri 4 - tetr(a) 4 - tetr(a) 5 - pent(a) 5 - pent(a) 6 - hex(a) 6 - hex(a) 7 - hept(a) 7 - hept(a) 8 - oct(a) 8 - oct(a) 9 - non(a) 9 - non(a) 10 - dec(a) 10 - dec(a)

PrefixesPrefixes Nonmetal rootsNonmetal roots H - hyd H - hyd C - carb C - carb N - nitr N - nitr P - phosph P - phosph As - arsen As - arsen O - ox O - ox S - sulf S - sulf Se - selen Se - selen F - fluor F - fluor Cl - chlor Cl - chlor Br - brom Br - brom I - iod I - iod

Practice problems:Practice problems:

COCO PP22OO55

CClCCl44 AsAs22OO33

NFNF33

SOSO22

Carbon monoxideCarbon monoxide Diphosphorus Diphosphorus

pentoxidepentoxide Carbon Carbon

tetrachloridetetrachloride Diarsenic trioxideDiarsenic trioxide Nitrogen trifluorideNitrogen trifluoride Sulfur dioxideSulfur dioxide

More practice…More practice…

HH22OO NHNH33

NN22HH44

NN22OO NONO

Di hydrogen Di hydrogen monoxidemonoxide

Nitrogen trihydrideNitrogen trihydride Dinitrogen Dinitrogen

tetrahydridetetrahydride Dinitrogen Dinitrogen

monoxidemonoxide Nitrogen monoxideNitrogen monoxide

WaterWater AmmoniaAmmonia HydrazineHydrazine Nitrous Nitrous

oxideoxide Nitric oxideNitric oxide

Naming AcidsNaming Acids

Molecules can be put in solution Molecules can be put in solution (water) and they make acids(water) and they make acids

If compound releases H+ ions when If compound releases H+ ions when put in water solution, it is an ACIDput in water solution, it is an ACID

Only name acids if molecule is put in Only name acids if molecule is put in water!!!water!!!

Two typesTwo types• Binary AcidsBinary Acids• OxyacidsOxyacids

Binary AcidsBinary Acids Hydrogen + one other elementHydrogen + one other element Sometimes there are more than 2 Sometimes there are more than 2

elementselements To name hydrogen, use prefix To name hydrogen, use prefix Hydro-Hydro- Root (or form of root) of the second Root (or form of root) of the second

element followed by suffix element followed by suffix –ic–ic• If there are more than 2 elements involved, the If there are more than 2 elements involved, the

root of the second part of the name is the root root of the second part of the name is the root of the polyatomic ion that acid containsof the polyatomic ion that acid contains

Add the word Add the word acid acid to the end to the end Example: HCNExample: HCN

• Hydrocyanic acidHydrocyanic acid Example: HClExample: HCl

• Hydrochloric acidHydrochloric acid

OxyacidsOxyacids Acids thant contain OXYANIONAcids thant contain OXYANION What is an oxyanion?What is an oxyanion?

• Polyatomic ion that contains oxygenPolyatomic ion that contains oxygen First: Determine anion presentFirst: Determine anion present Use a form of the root of the anionUse a form of the root of the anion Add suffixAdd suffix

• Anion suffix –ate….oxyacid suffix= -Anion suffix –ate….oxyacid suffix= -icic• Anion suffix –ite….oxyacid suffix= Anion suffix –ite….oxyacid suffix= -ous-ous

Add the word Add the word acidacid Example:HNOExample:HNO33

• Oxyanion: nitrate NOOxyanion: nitrate NO33--• Oxyacid name: nitric acidOxyacid name: nitric acid

Example:HNOExample:HNO22• Oxyanion: nitrite NOOxyanion: nitrite NO22--• Oxyacid: nitrous acidOxyacid: nitrous acid

PracticePractice

HIHI HClOHClO33

HH22SOSO44

HH22SS HClOHClO22

Hydroiodic acidHydroiodic acid Chloric acidChloric acid Sulfuric acidSulfuric acid Hydrosulfuric acidHydrosulfuric acid Chlorous acidChlorous acid

Writing formulasWriting formulas

Write the symbols for the Write the symbols for the elements in the order mentioned elements in the order mentioned in the name. in the name.

Write subscripts indicated by the Write subscripts indicated by the prefixes. If the first part of the prefixes. If the first part of the name has no prefix, assume it is name has no prefix, assume it is mono-.mono-.

PrefixesPrefixes tell you SUBscripts fro tell you SUBscripts fro each elementeach element

Writing Formulas for Binary Covalent Writing Formulas for Binary Covalent Compounds:Compounds: ExamplesExamples

nitrogen dioxide NO2

diphosphorus pentoxide P2O5

xenon tetrafluoride XeF4

sulfur hexafluoride SF6

11 monomono

22 didi

33 tritri

44 tetratetra

55 pentapenta

66 hexahexa

77 heptaaheptaa

88 octaocta

99 nonanona

1010 decadeca

* Second element * Second element in ‘ide’ fromin ‘ide’ from

* Drop –a & -o * Drop –a & -o before ‘oxide’before ‘oxide’

Air Pollution Class WorkAir Pollution Class Work

Many common Many common air pollutants air pollutants for acids when for acids when dissolved in a dissolved in a water solutionwater solution

Complete the Complete the following tablefollowing table

Formula Formula of of PollutantPollutant

Name of Name of MoleculeMolecule

Formula Formula of Acidof Acid

Name of Name of AcidAcid

SOSO22

Carbonic Carbonic acidacid

NONO22

HNOHNO33