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CHEMICAL BONDING111A13 143A 4A22A21 2 31 2 3-3456789 10 11 123 4 5 3 2 3 2 41 2 51 2 3 61 2 3 7155A2 2 2 3 4 5 177A166A2-1-2-1-2-1-2-1-188A2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 Neutral AtomPositive IonNegative IonbyDR. STEPHEN THOMPSONMR. JOE STALEYThe contents of this module were developed under grant award # P116B-001338 from the Fund for the Improvement of Postsecondary Education (FIPSE), United States Department of Education.However, those contents do not necessarily represent the policy of FIPSE and the Department of Education, andyou should not assume endorsement by the Federal government.

CHEMICAL lectronegativityRoad MapTypes Of BondingProperties Controlled By Chemical BondPolar BondsMetallic BondingIntermolecular ForcesIons: Counting Electrons And ProtonsIonic And Atomic RadiiIons And EnergyLithium FluorideCrystal PackingCrystal PackingCrystal PackingCovalent H2QuantizationBond Length And StrengthStrong And Weak BondsStrong And Weak BondsCovalent To MetallicElectron Delocalization

CHEMICAL loids22ALiGroup 18B0.82K3Mg1Ca4SrY0.79 0.89 1.1Cs0.7FrBaLa0.89 1.1Ra678910111.36 1.54 1.63 1.66 1.55 1.83 1.88 1.91 1.9ScTi0.82 0.95 1.22 A2.04 2.55 3.04 3.44 3.98Be0.93 1.31Na133ANonmetals0.98 pPuCuPd12C1.61 1.9AlSiNOF2.19 2.58 3.16PSCl1.65 1.81 2.01 2.18 2.55 2.96ZnGaGeAsSe1.93 1.69 1.78 1.96 2.05 2.1Ag2.28 2.54Cd2InSnSb2.04 2.33 2.02Te2BrI0NeArKr002.66 EsFmMdNoLrElectronegativity is the ability of an atom to attractshared electrons to itself.It is largely the difference between the electronegativities oftwo atoms which determines what kind of bond is formedbetween them.0He0RnWhat is the most electronegative element?What is the least electronegative element (aside fromthe noble gases)?What is the range of electronegativity for the metals?Metalloids? Nonmetals?Why is the electronegativity of the noble gases listedas zero?For an electron shared between hydrogen and chlorine,would you expect the electron to be closer to thehydrogen or the chlorine?2

CHEMICAL BONDINGROAD MAP3A 4A 5A 6A 7A 8A1A 2AHydrogenMetalsMetalloidsNonmetalsGroup 18HeHB C N O F NeLi BeAlCl ArV Cr Mn Fe Co Ni Cu Zn GaBr KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd InI XeNa MgK Ca Sc TiCs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra Ac Rf Ha Sg Ns Hs MtElectronegativityCe Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb LuTh Pa U Np Pu Am Cm Bk Cf Es Fm Md No LrIonicBondingGroups 1 and 2 MetalsNonMetals and HCovalentBondingNonMetals and HNonMetals and HPolarBondingOther MetalsNonMetals and HPolarBondingNon MetalloidsMetalloidsMetallicBondingMetalsMetals3

CHEMICAL BONDINGTYPES OF BONDINGThe different types of chemical bonding are determinedby how the valence electrons are shared among thebonded atoms.Filled electron shell coreValence Electron CloudIn IONIC BONDING the valence electrons are completely transferred from one atom to the other atom.Ionic bonds occur between metals and nonmetalswhen there is a large difference in electronegativity.Ionic BondingIn COVALENT BONDING the valence electrons areshared as pairs between the bonded atoms.Pure covalent bonding only occurs when two nonmetalatoms of the same kind bind to each other. When twodifferent nonmetal atoms are bonded or a nonmetal anda metal are bonded, then the bond is a mixture of covalent and ionic bonding called polar covalent bonding.Covalent BondingIn POLAR BONDING the electrons are shared butNOT equally. Many compounds have the characteristics of BOTH ionic and covalent bonding. Electronegativity differences determine the balance of character.Polar BondingIn METALLIC BONDING the valence electrons areshared among all of the atoms of the substance.Metallic bonding occurs when metals bond to eitherthemselves or mixed with other metals in alloys.Using the periodic table of electronegativities fromthe last page, write down examples of atom pairswhich you would expect to form covalent bonds,polar covalent bonds and ionic bonds.Metallic Bonding4

CHEMICAL BONDINGPROPERTIES CONTROLLED BY CHEMICAL BONDChemical bonding determines the physical propertiesof substances. These properties are listed below forcovalent, ionic and metallic bonding.CovalentGas, liquid, or a soft solid.Using the list of properties on the left, try to assignas many of the common substances in your environment to one of the types of bonding.Low melting point and low boiling point.Insoluble in H2OSoluble in nonpolar solvents.Nonconductor of heat and electricity.NonlustrousList and describe some substances which do notseem to fit into any of the three types of bonding.IonicCrystalline solid.Very high melting point.Soluble in H2O.Insoluble in nonpolar solvents.Nonconductor of heat and electricity.Conducts electricity in aqueous solutions.Examples: NaCl, CaCO3MetallicMalleable solid.High melting point and boiling point.Insoluble in H2O.Insoluble in nonpolar solvents.Conducts heat and electricity.LustrousExamples: gold, copper5

CHEMICAL BONDINGPOLAR BONDSIonic and covalent bonds are two ideal types.Many bonds share characteristics of both ionic andcovalent bonding. They are called polar covalentbonds and they tend to occur between atoms of moderately different electronegativities.In polar covalent bonds the electrons belong predominantly to one type of atom while they are still partiallyshared by the other type, as illustrated in the followingpictures of the valence electron densities.Separated AtomsValence electron(s)Filled electron shell coreIonic BondPolar Covalent BondCovalent BondUsing the chart of electronegativities, arrangethe following compounds in an order from mostionic to most covalent:Al2O3 , CaCl2 , NaF , O2 , NaCl,In the picture above, the separated atoms look alike.If, in fact, they are the same kind of atom, which ofthe three bonds shown is possible?Why only that one?What other type of bonding is possible betweenidentical atoms?6

CHEMICAL BONDINGMETALLIC BONDING‘ELECTRON SEA’ MODEL FOR METALSMetals are formed from elements on the left hand sideof the periodic table. Having generally low electronegativity they tend to lose their valence electrons easily.When we have a macroscopic collection of the sameor similar type of metallic atoms, the valence electronsare detached from the atoms but not held by any ofthe other atoms. In other words, these valence electrons are free from any particular atom and are onlyheld collectively by the entire assemblage of atoms.In a metal the ion cores are held more or less at fixedplaces in an ordered, or crystal, lattice. The valenceelectrons are free to move about under applied stimulation, such as electric fields or heat. e-e- e-e- e- e- e- e- e-1Picture 1 presents a regular arrangement of the ion coresfor a metal with a single valence electron per atom as wellas a snapshot of the location of the freely moving valenceelectrons.2 2 2 2 2 2 2 2 2 2Picture 2 shows a collection of ion cores for a metalwith two valence electrons. Draw in the valenceelectrons. (Little circles are good enough.)HINT: Metals are neutral in charge.What is the origin of electrical and thermalconductivity in sodium metal?Why do metals exhibit a wide range of melting points and hardness?7

CHEMICAL BONDINGINTERMOLECULAR FORCESIn addition to covalent, polar, ionic and metallic bonding there are intermolecular forces which contributeto the stability of things. These include dipole-dipoleforces, hydrogen bonding and London dispersionforces.DIPOLE-DIPOLE FORCESMany molecules are electric dipoles, that is, they havenet positive charge on one part of the molecule andnet negative charge on another part. Since oppositecharges attract and like charges repel, these moleculeswill tend to orient themselves so that there is the mostattraction and the least repulsion.Why is dipole-dipole interaction more important inliquids than in solids?Why is it more important in liquids than in gases?Can homonuclear diatomic molecules such as H2, O2and N2 have dipole-dipole forces?DIPOLE-DIPOLE INTERACTIONHYDROGEN BONDINGA particularly strong and important variety of dipoledipole interaction is called hydrogen bonding. Ahydrogen atom on one molecule is attracted to a highlyelectronegative atom in another molecule. Hydrogenbonding is strong both because of the high polarityinvolved and because the small size of the hydrogenatom permits a close approach between it and theelectronegative atomHYDROGENOXYGENHydrogen bonding is particularly noted between water molecules, but from the description given aboveyou should be able to deduce other substances inwhich hydrogen bonding occurs.HYDROGEN BONDINGLONDON DISPERSION FORCESEven nonpolar molecules have a random fluctuationof charge making the molecule temporarily polar. Thisthen induces an opposite fluctuation in a neighboringmolecules so that the two molecules have oppositecharges on their near sides and attract each other.inducedctm effequantuorF-FF-Fquantum effectinduced8WATERMOLECULE

CHEMICAL BONDINGIONS: COUNTING ELECTRONS AND PROTONSNEUTRAL ATOMSNeutral atoms have the same number of electrons asprotons. In the picture below, the nuclear charge isrepresented by the gray circle marked 3 , for the 3protons in the nucleus of lithium. Electrons are markedas horizontal dashes, one for each electron.POSITIVE IONSPositive ions have more protons than electrons.Since the number of protons an atom has is fixed inordinary chemical reactions, positive ions are producedby removing electrons from the atoms.Li Li3 3 In the pictures below draw in the number of electronsneeded to make the ion named in the box.In the pictures below, draw in the number of electrons required to make the atom neutral and write theelement symbol in the box to the left of the atom.Na 11 Mg2 12 8 9 NEGATIVE IONSNegative ions have more electrons than protons.Since the number of protons is unchanged from the neutralatom, negative ions are formed by the addition of electrons.In the pictures below draw in the number of electronsneeded to make the ion named in the box.11 O2-8 F-9 17 9

CHEMICAL BONDINGATOMIC AND IONIC RADIINeutral AtomPositive IonNegative Ion111A13 143A 4A22A21 2 31 2 3-3456789 10 11 123 4 5 3 2 3 2 41 2 51 2 3 61 2 3 7155A2 2 2 3 4 5 177A166A2-1-2-1-2-1-2-1-188A2 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 In this version of the periodic table the relative sizesof both neutral atoms and of their most common ionsare shown, as well as the charges on their ions. Theatoms are shown as black outline circles and the ionicdiameters are colored blue for positive ions and red fornegative ions.What makes the atoms and ions in the middle of periods 4, 5 and 6 so small? What makes the samariumatom so large?Identify the two kinds of atom which appear about thesame size as their ion and explain why this is so.Why are the positive ions smaller than their neutralatoms while the negative ions are larger than theneutral atoms?Why are the antimony and beryllium ions so small?Differentiate between the causes.Why are the Lanthanide ions of such similar size?Why do both ions and atoms tend to grow larger aswe go down the periodic table?How might you use the chart of atomic and ionic radiito explain the strengths of ionic bonding betweenvarious ions?What is the smallest atom? What atom has thesmallest ion (too small to show on the table)? Findthe largest atom and identify it on a standard periodictable.Compare the ionic and atomic radii table above withthe chart of electronegativities and attempt to explainas many aspects of the sizes of atoms and ions interms of electronegativity as possible.What kind of ions do atoms with large electronegativities tend to form?10

CHEMICAL BONDINGIONS AND ENERGYeAdd Energy00e- The diagrams above show the ground state of thelithium atom, followed by an excited state, followedby the lithium ion with the free electron. What is thecharge of the lithium ion in the right hand drawing?In the diagrams above, draw in the electrons as arrows which occupy the ground state orbitals of thesodium atom in the left hand picture. In the righthand picture draw in the orbitals and electrons of thesodium ion.e-e00 0ENERGYENERGY0ENERGY0 0ENERGYENERGY0Add More Energy Energy The diagrams above show the ionization of fluorine.What is the charge of the fluoride ion?In the diagrams above, draw in the electrons (arrows)for the chlorine atom on the left and for the chlorideion on the right. What is the charge of the chlorideion?11

CHEMICAL BONDINGLITHIUM FLUORIDE2Li(s) 2Li(g)It requires 155 kJ/molto separate lithium atomsfrom their body centeredcubic crystalstructure.2Li(g) 2Li (g) 2e-(g)It requires 520 kJ/molto ionize lithium atoms.e LiLi Add the energies which areassociated with the processa making lithium fluoridecrystal lithium crystal anddifluoride molecules. Is thenet reaction endothermic orexothermic? F2(g) 2F(g)It requires 80 kJ/molto dissociate the difluoridemolecule. e-2F(g) 2e-(g) 2F-(g)Ionization of the fluorineatom gives off 328 kJ/molof energy. F-F2Li (g) 2F-(g) 2Li F-(s) – Combining the lithium andfluoride ions into their crystalgives off 1030 kJ/mol ofenergy.12Li

CHEMICAL BONDINGCRYSTAL PACKINGThe picture at left shows sevenspheres packed as close together as possible in the plane.This is called close packing.How many gray spheres touchthe green sphere?1Using circles, sketch in the box above another way totile the plane.2The picture above shows how close packing canfill, or tile, the plane. Notice the little triangles (withcurved sides) that lie in between the spheres. Someof them point up and some of them point down.Compare the number of each kind of triangle.Picture 3 is simply picture 2 looke