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Valence bond theory

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tied to Lewis's idea of bonding electron pairs between atoms and lone pairs of electrons localized on a particular atom

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molecular orbital theory

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derives molecular orbitals that are spread out (delocalized) over the molecule by combining atomic orbitals to form a set of orbitals that are the property of the molecule, and then distribute the electrons of the molecule w/in these orbitals

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orbital overlap

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increases the probability of finding the bonding electrons in the region of space b/w the two nuclei

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sigma bond

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covalent bond from the overlap of two s orbitals, one from each of two atoms. the electron density is greatest slong the axis of the bond

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orbital hybridization

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a new set of orbitals (hybrid orbitals) can be created by mixing the s, p, and d atomic orbitals on an atom. # hybrid orbitals = # mixed atomic orbitals. hybrid orbital sets are built by combining an s orbital with as many p orbitals (and d orbitals if necessary) to have enough hybrid orbitals to accommodate the bond and lone pairs on the central atom. the hybrid orbitals are directed toward the terminal atoms, leading to better orbital overlap and stronger bond b/w the central and terminal atoms

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choosing hybridization

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hybrid orbitals required by an atom in a molecule or ion are chosen to match the electron pair geometry of the atom b/c a hybrid orbital is required for each sigma bond electron air and each lone pair

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types of hybridization: sp

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if the valence shell s orbital on the central atom in a molecule or ion is mixed with a valence shell p orbital on that same atom, two sp hybrid orbitals are created and separated by 180 degrees

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types of hybridization: sp^2

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if an s orbital is combined with two p orbitals, all in the same valence shell, three sp^2 hybrid orbitals are created, in the same plane separated by 120 degrees

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types of hybridization: sp^3

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when the s orbital in a valence shell is combined with three p orbitals, the result is four hybrid orbitals, each labeled sp^3, separated by 109.5 degrees (tetrahedral)

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types of hybridization: sp^3d and sp^3d^2

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if one or two d orbitals are combined with s and p orbitals in the same valence shell, two other hybrid orbital sets are created. these are utilized by the central atom of a molecule or ion with a trigonal-bipyramidal or octahedral electron-pair geometry

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pi bond

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the overlap region is above and below the internuclear axis, and the electron density is above and below the bond axis

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forming pi bonds

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can form only if (a) there are unhybridized p orbitals on adjacent atoms and (b) the p orbitals are perpendicular to the plane of the molecule and parallel to one another

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isomer

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compound that has the same formula but different structure

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bonding molecular orbital

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molecular orbital in which the energy of the electrons is lower than that of the parent orbital electrons (is a sigma orbital)--increased probability that electrons will reside in the bond region b/w the two nuclei

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antibonding molecular orbital

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molecular orbital in which the energy of the electrons is higher than that of the parent orbital electrons (is a sigma orbital)--decreased probability that electrons will reside in the bond region b/w the two nuclei, so the nuclei repel one another. system is destabalized b/c energy of system is higher than that of the atoms themselves

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bond order

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1/2 (number of electrons in bonding MOs - number of electrons in antibonding MOs)

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heteronuclear diatomic molecules

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molecule composed of two atoms of different elements

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ways carbon reaches octet

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1)by forming four single bonds, 2)by forming a double bond and two single bonds, 3)by forming two double bonds, 4)by forming a triple bond and a single bond

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structural isomers

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compounds having the same elemental composition but the atoms are linked together in different ways

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stereoisomers

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compounds with the same formula and in which there is similar attachment of atoms, where the atoms have different orientations in space. two types: geometric and optical isomers

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geometric isomers

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isomers in which the atoms of the molecule are arranged in different geometric relationships (cis and trans)

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optical isomers

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molecules that have nonsuperimposable mirror images

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chiral

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molecules that have nonsuperimposable mirror images

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enantiomers

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pairs of nonsuperimposable molecules. pure samples have same physical properties and pairs rotate polarized light to an equal extent in opposite directions

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hydrocarbon

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compounds made of carbon and hydrogen only (subgroups: alkanes, cycloalkanes, alkenes, alkynes, aromatic compounds)

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alkanes

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general formula CnH2n+2, often called saturated compounds (each C atoms is attached to four other atoms). as the # of C atoms in an alkane increases, the # of possible structural isomers increases

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alkyl groups

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hydrocarbon substituents

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properties of alkanes

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some are gases at room temp, higher molar mass compounds are liquids or solids (MP and BP increases with molar mass, representing increased forces of attraction b/w molecules). pure alkanes are colorless, gases and liquids have odors, all are insoluble in water (since they're nearly nonpolar), burn readily in air, low chemical reactivity

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cycloalkanes

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constructed with tetrahedral carbon atoms joined together to form a ring

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strained hydrocarbons

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C-C bonds are weaker and the molecules readily undergo ring-opening reactions that relieve the bond angle strain

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alkenes

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hydrocarbons with 1+ C=C double bonds (double bonds add possibility of geometric isomerism and increased reactivity), general formula CnH2n

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alkynes

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compounds with carbon-carbon triple bond, gen formula CnH2n-2

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properties of alkenes and alkynes

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colorless, low-molar-mass compounds are gases, others are liquids or solids. unsaturated compounds. carbon atoms liked by double bond are bonded to only 3 atoms; in alkynes, are bonded to 2 atoms

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addition reactions

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molecules with the general formula X-Y add across the carbon-carbon double bond to increase the number of groups attached to carbon. products are often substituted alkanes

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Markovnikov's rule

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when a reagent HX adds to an unsymmetrical alkene, the hydrogen atom in the reagent becomes attached to the C that already has the lagest # of hydrogens

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hydrogenation

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reagent added to a double bond is hydrogen (X-Y=H2)

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properties of aromatic compounds

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colorless liquids or solids, insoluble in water, soluble in nonpolar solvents, oxidezed by O2 to form CO2 and H2O, unsaturated hydrocarbons

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resonance stabilization

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extra stability of pi bonding

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functional group

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an atom or group of atoms attached to a C atom in the hydrocarbon, formula written as R-X in which R is a hydrocarbon lacking a H atom, X is the functional group that replaced the H

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alcohol

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when one of the H atoms of an alkane is replaced by a hydroxyl (-OH) group

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ether

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any of a class of organic compounds characterized by the presence of an oxygen atom singly bonded to two carbon atoms

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amines

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one or more H atoms of NH3 are replaced with an organic group. trigonal pyramidal structure. chategorized based on # of organic substituents as primary(one organic group), secondary(2), tertiary(3). offensive odors

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carbonyl group

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functional group that characterizes aldehydes and ketones, consisting of a carbon atom doubly bonded to an oxygen atom

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aldehydes

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RCHO, have an organic group (-R) and a H atom attached to a carbonyl group

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ketones

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RCOR', have two -R groups attached to the carbonyl carbon; may be the same groups or diff groups

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carboxylic acids

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RCO2H, have an -R group and an -OH group attached to the carbonyl carbon

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esters

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RCO2R', have -R and -OR' groups attached to the carbonyl carbon

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amides

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RCONR2',RCONHR',RCONH2, have an -R group and an amino group (-NH2,-NHR,-NR2) bonded to the carbonyl carbon

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primary alcohols

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one carbon and two hydrogen atoms attached to the C atom bearing the -OH group. oxidized in two steps: to an aldehyde then to a carboxylic acid

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secondary alcohols

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two carbon atoms and one hydrogen atom attached to the C atom bearing the -OH group. oxidation produces a ketone

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tertiary alcohols

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have three carbon atoms attached to the C atom bearing the -OH . do not react with usual oxidizing agents

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aldehydes

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any of a class or organic compounds characterized by the presence of a carbonyl group, in which the carbon atom is bonded to at least one H atom. pleasant odors. oxidation products of primary and secondary alcohols

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ketones

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any of a class of organic compounds characterized by the presence of a carbonyl group, in which the carbon atom is bonded to two other carbon atoms. pleasant odors. oxidation products of primary and secondary alcohols

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carboxylic acid

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any of a class of organic compounds characterized by the presence of a carboxyl group. reactions with bases gives carboxylate anions

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esterification reaction

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carboxylic acids (RCO2H) reacts with alcohols (R'OH) to form esters (RCO2R'). the OR group of the alcohol ends up as part of the ester

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hydrolysis

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reaction that is the reverse of the formation of the ester, generally done in the presence of a base, producing the alcohol and a sodium salt of the carboxylic acid

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amides

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form when an acid reacts with an amine, with a loss of water. have an organic group and an amino group attached to the carbonyl group

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polymers

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giant molecules made by chemically joining many small molecules called monomers

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thermoplastics

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soften and flow when heated and harden when cooled

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thermosetting plastics

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initially soft but set to a solid when heated and cannot be resoftened

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addition polymers

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made by directly adding monomer units together (ex PVC)

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condensation polymers

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made by combining monomer units and splitting out a small molecule (often water)

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elastomers

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synthetic organic polymers with very high elasticity

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copolymers

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formed by polymerization of two or more different monomers

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condensation reaction

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two molecules react by splitting out, or eliminating, a small molecule

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polyester

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condensation polymer formed by elimination of water b/w two types of monomers, one with two carboxylic acid groups and the other w/two alcohol groups

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polyamide

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condensation polymer formed by elimination of water b/w two types of monomers, one with two carboxlic acid groups and the other with two amine groups

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Boyle's law

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the volume of a fixed amount of gas at a given temperature is inversely proportional to the pressure exerted by the gas. PV=P'V'

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Charles's Law

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the volume of a fixed quantity of gas at constant pressure decreases with decreasing temperature. V/T=V'/T'

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Avagadro's hypothesis

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equal volumes of gases under the same conditions of temperature and pressure have equal numbers of particles (PV=nRT)

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Dalton's law of partial pressures

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the pressure of a mixture of ideal gases is the sum of the partial pressures of the different gases in the mixture

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mole fraction, X

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number of moles of a particular substance in a mixture divided by the total number of moles of all substances present

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diffusion

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mixing of molecules of two or more gases due to their random molecular motions

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effusion

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movement of gas through a tiny opening in a container into another container wher the pressure is very low

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ion-dipole forces

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forces of attraction b/w a positive or negative ion and polar molecules, depends on distance, charge on ion, and magnitude of dipole

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enthalpy of solvation/hydration

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enthalpy change associated with the hydration of ions/in water (depends on 1/d)

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hydrogen bond

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extreme form of dipole-dipole interaction where one atom involved is always H and the other is highly electronegative

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