covalent bonds part 2
TRANSCRIPT
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