Carbon Compounds and Chemical Bonds

Carbon Compounds and Chemical BondsChapter 1ORGANIC CHEMISTRYSTUDY OFCARBONCONTAININGCOMPOUNDSCompounds from Nature

Synthetic compounds: invented by organic chemists and prepared in their laboratoriesFriedrich Woehlers urea synthesisAmmonium isocyanate + heat ------> ureaNH4CNONH2CONH2I have been able to make urea without aid of kidney of man or dog.18281828Some organic chemicals

DNA

Essential oils

MedicinesActive Pharmaceutical IngredientsExcipients

Materials

Fuels

PigmentsWITH ITSELF

No limitAND Electronic Structure of AtomsStructure of atomsa small dense nucleus, diameter 10-14 - 10-15 m, which contains positively charged protons, neutrons and most of the mass of the atomextranuclear space, diameter 10-10 m, which contains negatively charged electrons

Notice: one s orbital in each principal shell three p orbitals in the second shell (and in higher ones) five d orbitals in the third shell (and in higher ones)Rules for Electron Configurations

Capacities of shells (n) and subshells (l)Electronic Structure of AtomsElectrons are confined to regions of space called principle energy levels (shells)each shell can hold 2n2 electrons (n = 1, 2, 3, 4......)

Electronic Structure of AtomsShells are divided into subshells called orbitals, which are designated by the letters s, p, d,........s (one per shell) p (set of three per shell 2 and higher) d (set of five per shell 3 and higher) .....

Electronic Structure of AtomsRule 1: orbitals fill from lowest energy to highest energyRule 2: only two electrons per orbital, spins must be pairedRule 3: for a set of orbitals with the same energy, add one electron in each before a second is added in any one

Periodic Behavior of ElementsFlame tests: elements with low first ionization energies are excited in a flame, and often emit in the visible region of the spectrum Atoms emit energy when electrons fall from higher to lower energy states

BaSrCaKNaLi

Atomic Spectrum of HydrogenElectronic Structure of AtomsThe pairing of electron spins

Lewis StructuresGilbert N. LewisValence shell: the outermost electron shell of an atomValence electrons: electrons in the valence shell of an atom; these electrons are used in forming chemical bondsLewis structure the symbol of the atom represents the nucleus and all inner shell electronsdots represent valence electronsFor Nitrogen atom: Valence shell of Nitrogen= 3Number of valence electrons of Nitrogen = 5 Lewis StructuresLewis structures for elements 1-18 of the Periodic Table

For Nitrogen atom: Valence shell of Nitrogen= 3Number of valence electrons= 5 Lewis Model of BondingAtoms bond together so that each atom in the bond acquires the electron configuration of the noble gas nearest it in atomic numberan atom that gains electrons becomes an anionan atom that loses electrons becomes a cationIonic bond: a chemical bond resulting from the electrostatic attraction of an anion and a cationCovalent bond: a chemical bond resulting from two atoms sharing one or more pairs of electronsWe classify chemical bonds as ionic, polar covalent, and nonpolar covalent based on the difference in electronegativity between the atomsElectronegativityElectronegativity: a measure of the force of an atoms attraction for the electrons it shares in a chemical bond with another atomPauling scaleincreases from left to right within a periodincreases from bottom to top in a group

Electronegativity

Electronegativity of atoms (Pauling scale)

ElectronegativityElectronegativity and chemical bonding

Example: NaClNa = 0.8, Cl = 3.0Difference is 2.2, sothis is an ionic bond!

Coulombs LawThe energy of interaction between a pair of ions is proportional to the product of their charges, divided by the distance between their centers

What forces that hold atom together within molecules?

Covalent Bonding Forces Electron electron repulsive forces Proton proton repulsive forces Electron proton attractive forces

Bond Length DiagramNet repulsionNet attractionScientists can determine the internuclear distances that correspond to the lowest energy states of molecules http://ch301.cm.utexas.edu/simulations/bond-strength/BondStrength.swfBond Length and EnergyBondBond typeBond length (pm)Bond Energy(kJ/mol)C - CSingle154347C = CDouble134614C CTriple120839C - OSingle143358C = ODouble123745C - NSingle143305C = N Double138615C NTriple116891Bonds between elements become shorter and stronger as multiplicity increasesCovalent BondsA covalent bond forms when electron pairs are shared between two atoms whose difference in electronegativity is 1.9 or lessan example is the formation of a covalent bond between two hydrogen atomsthe shared pair of electrons completes the valence shell of each hydrogen.

Polar Covalent BondsIn a polar covalent bondthe more electronegative atom has a partial negative charge, indicated by the symbol d-the less electronegative atom has a partial positive charge, indicated by the symbol d+in an electron density modelred indicates a region of high electron density blue indicates a region of low electron density

Polar and Nonpolar Moleculesammonia and formaldehyde are polar moleculesacetylene is a nonpolar molecule

Carbon Intro and ReviewAtomic StructureAtoms made up of protons, neutrons, electronsIsotopes same # protons; different # neutronsElectronic StructureElectrons determine structuregive rise to bondingbehave like wavesorbitals (s, p)

Orbital overlap to form bonds.

Orbital overlap to form p bonds.Electron Probabilitiesand the 1s OrbitalThe 1s orbital looks very much like a fuzzy ball, that is, the orbital has spherical symmetryThe electrons are more concentrated near the center

Spherical symmetry; probability of finding the electron is the same in each direction.The electron cloud doesnt end here the electron just spends very little time farther out.Electron Probabilitiesand the 2s OrbitalThe region near the nucleus is separated from the outer region by a spherical node - a spherical shell in which the electron probability is zero

The 2s orbital has two regions of high electron probability, both being sphericalThe Three p Orbitals

2p

The Five d Orbitals3dRules for Electron ConfigurationsSubshell filling order ...

Each subshell must be filled before moving to the next level1s22s22p63s23p6 ...1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s

The most stable arrangement of electrons in subshells is the one with the greatest number of parallel spins (Hunds rule).

C 1s22s22p2N 1s22s22p3O 1s22s22p4F 1s22s22p5Ne 1s22s22p6

Periodic RelationshipsThe valence shell is the outermost occupied shellThe period number = principal quantum number, n, of the electrons in the valence shellAtomic Orbitals1s 1st orbitals type (spherical)1s, 2s, 3s

Atomic Orbitals2s orbital (spherical)

Atomic Orbitalsp (2p, 3p)3 orbitals oriented perpendicular to each otherhave node (region of 0 e- density)nodal plane

2p orbital

Atomic Orbitalsp (2p, 3p)3 orbitals oriented perpendicular to each otherhave node (region of 0 e- density)nodal planeshapedumbbell

Chapter 1Electronic Configuration of AtomsAufbauFill lowest energy orbital 1stHunds Rule1 e- into each orbital of = energy

Pauli Exclusion PrincipleElectrons in the same orbital are spin pairedElectronic Configurations

WHY DO HYBRIDS ?? 1. Electron pair repulsions are minimized (= lower energy)2. Stronger bonds (= lower energy) are formed3. Hybrids have better directionality for forming bondsShapes of Atomic OrbitalsAll s orbitals have the shape of a sphere, with its center at the nucleus of the s orbitals, a 1s orbital is the smallest, a 2s orbital is larger, and a 3s orbital is larger still

Shapes of Atomic OrbitalsA p orbital consists of two lobes arranged in a straight line with the center at the nucleus

Orbital Overlap ModelA covalent bond forms when a portion of an atomic orbital of one atom overlaps a portion of an atomic orbital of another atomin forming the covalent bond in H-H, for example, there is overlap of the 1s orbitals of each hydrogen

Hybrid OrbitalsWe will study three types of hybrid atomic orbitalssp3 (one s orbital + three p orbitals give four sp3 orbitals)sp2 (one s orbital + two p orbitals give three sp2 orbitals)sp (one s orbital + one p orbital give two sp orbitals)Overlap of hybrid orbitals can form two types of bonds, depending on the geometry of the overlap bonds are formed by direct overlap bonds are formed by parallel overlapsp3 Hybrid OrbitalsEach sp3 hybrid orbital has two lobes of unequal sizeThe four sp3 hybrid orbitals are directed toward the corners of a regular tetrahedron at angles of 109.5

sp3 Hybrid Orbitalsorbital overlap bonding in water, ammonia, and methane

sp2 Hybrid OrbitalsAn sp2 hybrid orbital has two lobes of unequal size the three sp2 hybrid orbitals are directed toward the corners of an equilateral triangle at angles of 120the unhybridized 2p orbital is perpendicular to the plane of the three sp2 hybrid orbitals

a carbon-carbon double bond consists of one sigma (s) bond and one pi (p) bondsp2 Hybrid Orbitalssp2 Hybrid Orbitalsa carbon-oxygen double bond also consists of one sigma (s) bond and one pi (p) bond

sp Hybrid OrbitalsEach sp hybrid orbital has two lobes of unequal sizethe two sp hybrid orbitals lie in a line at an angle of 180the two unhybridized 2p orbitals are perpendicular to each other and to the line through the two sp hybrid orbitals

sp Hybrid Orbitalsa carbon-carbon triple bond consists of one sigma (s) bond and two pi (p) bondsHybrid OrbitalsSummary of orbitals and bond types

Examples of sigma bonds formed from sp3 hybrid orbitals

Orbital overlap to form bonds.

Orbital overlap to form p bonds.

......

Examples of natural acyclic compounds, their sources (in parentheses), and selected characteristics

Examples of natural heterocyclic compounds having a variety of heteroatoms and ring sizes.

Examples of natural carbocyclic compounds with rings of various sizes and shapes.

IsomerismThe Molecular Formula of a substance gives the number of different atoms present.The Structural Formula indicates how those atoms are arranged.

Isomers are molecules with the same number and kinds of atoms but different arrangements of the atoms. Structural (or Constitutional) isomers have the same molecular formula but different structural formulas.

Constitutional Isomerismthe potential for constitutional isomerism is enormous

World populationis about6,000,000,00074Condensed Structural Formulas

75Cyclic Molecules

76Bond-line Formulas

77

In this representation, bonds that project upward out of the plane of the paper are indicated by a wedge, those that lie behind the plane are indicated with a dashed wedge, and those bonds that lie in the plane of the page are indicated by a line.

78Three-Dimensional Formulaswriting structural FormulasIn a continuous chain, atoms are bonded one after another.

In a branched chain, some atoms form branches from the longest continuous chain.

Abbreviated Structural Formulas

Formal ChargeHere, some molecules one or more atoms maybe charged +ve or ve which comes from the chemical reactions.Its important to know how to tell where the charge is located.

H3O+Formal ChargeThe formal charge on an atom in a covalently bonded molecule or ion is the number of valence electrons in the neutral atom minus the number of covalent bonds to the atom and the number of unshared electrons on the atom.

ResonanceResonance structures of a molecule or ion are two or more structures with identical arrangements of the atoms but different arrangements of the electrons. If resonance structures can be written, the true structure of the molecule or ion is a resonance hybrid of the contributing resonance structures.

Resonance

Physical measurements tell us that none of the foregoing structures accurately describes the real carbonate ion.Experimentally, It was found that all three carbonoxygen bond lengths are identical: 1.31 . This distance is intermediate between the normal C=O (1.20 ) and C-O (1.41 )The real carbonate ion has a structure that is a resonance hybrid of the three contributing resonance structures