BONDING Chemical Bond
BONDINGChemical BondAttraction that holds atoms together Types include IONIC, METALLIC, or COVALENT Differences in electronegativity determine the bond typeElectrostatic AttractionTwo objects near each other withdifferent / opposite electrical charges Forces of attraction that allow atoms to bond /- ionsattracted to each other in an ionic bond OR the positivenuclei attracted to the shared e- in covalentIonic BondTRANSFER of electrons between atoms Each atom achieves a noble gasconfiguration (full valence shell) Usually between a METAL and aNONMETAL Formula Unit: lowest wholenumber ratio of ions in an ioniccompound (ex: NaCl or MgCl2)Ionic Bonding How to show using Electron Dot Structures:1) Draw the dot structure for eachelement in the ionic compound2) Determine which element will lose eand which will gain e- and how many3) Use arrows to show the e- beingtransferred to an empty space on theanion s dot structure4) Continue until each element has acomplete octet add more of eachelement as neededIonic Bonding EXAMPLE:Show the electron dot structures for sodium and chlorineusing arrows to indicate the transfer of e-.Na Wants to lose ONEelectron!Cl-Wants to gain ONEelectron!1
Ionic BondingIonic Bonding EXAMPLE:Show the electron dot structures for sodium and chlorineusing arrows to indicate the transfer of e-. EXAMPLE:Show the electron dot structures for sodium and chlorineusing arrows to indicate the transfer of e-.Na Cl-Na To write the formula unit for the compound:write the element symbol for the cation followedby the anion symbol to indicate the # of eachuse subscripts (none needed if just one)!!Ionic Bonding EXAMPLE:Show the electron dot structures for calcium andphosphorus using arrows to indicate the transfer of e-.CaPWants to lose TWOelectrons!Wants to gain THREEelectrons!Ionic Bonding EXAMPLE:Show the electron dot structures for calcium andphosphorus using arrows to indicate the transfer of e-.Ca 2 CaP3-CALCIUM STILLNEEDS TO LOSE ONEMORE ELECTRON!!!!Cl-NaClIonic Bonding EXAMPLE:Show the electron dot structures for calcium andphosphorus using arrows to indicate the transfer of e-.CaCa2 PPHOSPHORUSSTILL NEEDSONE MOREELECTRON!!!!Ionic Bonding EXAMPLE:Show the electron dot structures for calcium andphosphorus using arrows to indicate the transfer of e-.Ca 2 CaPP3-2
Ionic Bonding EXAMPLE:Show the electron dot structures for calcium andphosphorus using arrows to indicate the transfer of e-.CaCa 2 Ca2 PP3-Ionic Bonding MORE EXAMPLES:Show the electron dot structures for each pair and showthe transfer of electrons using arrows. Be sure to includethe charge on each ion after the transfer and write theformula unit.Ionic Bonding EXAMPLE:Show the electron dot structures for calcium andphosphorus using arrows to indicate the transfer of e-.CaCa 2 Ca 2 2 PP33-Ca3P2Coulomb’s LawDetermines the energy / strength of an ionic bondLITHIUM and FLUORINEALUMINUM and SULFURMAGNESIUM and CHLORINEPOTASSIUM and OXYGENCoulomb’s LawDetermines the energy / strength of an ionic bondForce of attraction between two oppositelycharged particles is directly proportional tothe MAGNITUDE of the charges and*Applies inversely proportional to the DISTANCEbetween those charges to PES!GREATER charges GREATER attractionCLOSER (smaller ions) GREATER attraction(Attraction à Opposites / Repulsion à Same)*When calculated for an ionic compound, energy isNEGATIVE, indicating an attractive force that hasa LOWER energy than the separated ions!!r distance between ions in nm (SIZE MATTERS!)Q1 and Q2 numerical ion charges (with signs)F electrical force between the atomsLattice EnergyChange in energy that takes place when separatedGASEOUS ions are packed together to form an ionicsolid (tells how much energy needed to separate ions) Ionic compounds form solidcrystals organized in a CRYSTALLATTICE of alternating and – ions Relates to Coulomb’s Law:GREATER charges and SMALLERsize mean HIGHER lattice energy(STRONGER BOND!)Can be used to help determineproperties of ionic compounds 3
Lattice EnergyEnergy needed to separate ions(how strong is the ionic bond)Lattice EnergyEnergy needed to separate ions(how strong is the ionic bond)SMALLER ions of the same charge STRONGER bond!GREATER charge STRONGER bond!Lattice EnergyEnergy needed to separate ions(how strong is the ionic bond)Lattice EnergyCalculate the DH f for Sodium Chloride:Na(s) ½ Cl2(g) à NaCl(s)Lattice Energy-786 kJ/molIonization Energy for Na495 kJ/molElectron Affinity for Cl*Notice the - energy indicating the ions areattracted and the lattice energy is high becauseboth atoms have a small atomic size!Ionic Compounds-349 kJ/molBond energy of Cl2239 kJ/molEnthalpy of sublimation for Na109 kJ/molNa(s) à Na(g)Na(g) à Na (g) e½ Cl2(g) à Cl(g)Cl(g) e- à Cl-(g) Na (g) Cl-(g) à NaCl(s)Na(s) ½ Cl2(g) à NaCl(s) 109 kJ 495 kJ ½(239 kJ)- 349 kJ-786 kJ-412 kJ/molProperties of Ionic Compounds1) STRONGLY bonded: strongattraction between the ions Formed from METAL and NONMETAL ionsbonded together2) Solid CRYSTAL latticestructure Known as “SALTS” Formed from regular repeating arrangement offormula units4
Properties of Ionic Compounds3) HIGH melting point and boilingpoint due to the strong attractionsbetween ions and the stable structureProperties of Ionic Compounds5) Conduct ELECTRICITY when melted ordissolved in water (because they form ions) too orderly when solid4) SOLUBLE in water /DISSOCIATE (breakapart into ions)Properties of Ionic CompoundsLattice Energy and Properties*Make sure youmention BOTHsubstances / ionsin an AP answer!!6) Extremely BRITTLE if you hit them hard enoughthey will shatter because they don t want to bend andthere will be a strong repulsive force - - - - Metallic Bonds - - - - - - Attraction of the FREE-FLOATING valenceelectrons for the positively charged metal ions Forces of attraction holdmetals together Not ionic Have similar properties toionic compounds Metals weakly hold on totheir valence e Positive ions (cations) arefloating in a “SEA OFELECTRONS” Which has a STRONGER bond? NaCl or KCl Which is more SOLUBLE in water? NaCl or AlCl3“Sea of Electrons” ELECTRONS ARE FREE TO MOVE!!5
Properties of MetalsProperties of Metals1) Malleable2) Ductile3) ConductiveAll due to the fact that theirvalence electrons are MOBILE!Electrons allow the atoms ofmetals to SLIDE like grease!AlloysWhy Make Alloys?Mixtures of two or more elements with atleast one being a metal Properties are SUPERIOR toindividual elements Sterling Silver (92.5% Ag,7.5% Cu): harder, moredurable than pure Ag / softenough to work Formed by melting a mix of ingredients andthen cooling Examples: brass (Cu and Zn), bronze (Cu andSn), and steel (Fe, C, etc.)Covalent BondSHARING of electrons between atoms Steels: corrosion resistant,ductile, hard, tough, and costeffective*MORE TO COME INSECTION 3!Bond LengthDistance where energy is at a MINIMUM Involves two NONMETALS Known as covalent or molecularcompounds MOLECULE: group of atoms joined by acovalent bond DIATOMIC MOLECULES: elementsthat cannot exist as single atomsEx: H2, N2, O2, F2, Cl2, Br2, and I2 When two atoms approach, two “bad” things occur electron/electron repulsion and proton/proton repulsion One “good” thing occurs proton/electron attraction When ATTRACTIVE forces offset REPULSIVE forces,energy decreases and a bond is formed Always lookingfor LOWEST energy!6
Bond LengthDistance where energy is at a MINIMUMBond LengthDistance where energy is at a MINIMUM*Note how to findthe bond lengthand energy fromthe graph!!Properties of Covalent CompoundsDissociation vs. DissolvingDISSOCIATIONCl-Na 1) Low melting and boiling points2) Don’t usually conduct electricity3) Not usually soluble in water (some dissolvebut don’t dissociate SUGAR!)4) Don’t form crystals (most liquids or gases atroom temperature)Properties of Covalent CompoundsCl-Na Cl-C12H22O11Na Cl-DISSOLVINGNa Salt IONICC12H22O11C12H22O11C12H22O11Sugar COVALENTAttractions and Properties Wide range of physical properties among covalentcompounds due to varying intermolecular attractions NETWORK SOLIDS: very stable structure consistingof all atoms being covalently bonded to each other-High melting points (1000 C or higher)-To melt, ALL the covalent bonds need to be brokenEX: DiamondsSiO2SiC7
Types of Covalent BondingBond Length There are three types of covalent bonds:1) SINGLE: sharing of only one pair of e- (2 total)2) DOUBLE: sharing of two pairs of e- (4 total)3) TRIPLE: sharing of three pairs of e- (6 total)As the number of bonds between two atomsINCREASE, the bond length DECREASES thebonds become SHORTER and STRONGER!!Remember the octet rule EIGHT electrons are needed!!Molecular Dot StructuresWHY?: More electrons between the nuclei whichDECREASES nuclear repulsions and INCREASESnucleus to electron attractions!!Molecular Dot Structures How to draw a structure:1) Determine the TOTAL number of valence eavailable for the entire molecule from theamount each element has. This is the # of ethat MUST be in the final structure Visual representation of how the atoms arebonded together in a molecule Shows valence e- as dots can see type ofcovalent bond as well (sharing of TWO dots aSINGLE bond)Molecular Dot Structures How to draw a structure:6) Total the e- in the molecule and see if totalfrom step #1 is reached. If so, then done7) If OVER the #, add double or triple bondsand remove pairs. If UNDER the #, add lonepairs (extra) to the center atom3) Whatever atoms are remaining in theformula go around the “center” (evenlydistributed when possible)HONC 1234Certain elements USUALLY have a specific numberof bonds (shared pairs) in a molecule!!!4) Any atoms next to the center need toSHARE at least a pair of electrons betweenthe atoms (covalent bonding). Insert pairs ofe- between bonded atoms5) Give each atom a complete octet by addingUNSHARED (lone) pairs until each atom is“happy” with its number2) Position any C or N atoms in the center With atoms other than C or N, put the leastelectronegative atom in the center (usually theatom that there is LESS of in the formula). Hnever in center unless it’s the only elementHydrogen – 1 bondOxygen –DO NOT overfillan atom svalence shell Ex: H onlywants twoelectrons!!2 bondsAtoms stillneed a FULLvalence!!Nitrogen – 3 bondsCarbon –4 bondsHONC IF YOU LOVE CHEMISTRY!!8
Molecular Dot Structures EXAMPLE:Molecular Dot Structures EXAMPLE:Write the dot structure for: NH3Write the dot structure for: H2OMolecular Dot StructuresMolecular Dot Structures EXAMPLE:Write the dot structure for: CO2 EXAMPLES:Write the dot structure for:Write the dot structure for:Exceptions to the Octet RuleIf the number of electrons doesn t work out 1) H - full valence shell is 2 e2) B - generally satisfied with 6 valence e3) Be - generally satisfied with 4 valence e4) N - can be satisfied with 7 valence e5) As, S, I, Se, P, etc. can expand theiroctet to have 10, 12, or 14 valence e-Exceptions to the Octet RuleWhy are some elements able toEXPAND their octet and take morethan EIGHT? Can occur when an element has an EMPTYd-orbital Electrons get put in there! Notice this only occurs in elements in the3rd period or higher WHY? Ex: Phosphorus9
Structural FormulasHOHèStructural FormulasH OHN NèN N Uses a dash (–) to represent a covalent bond Uses a dash (–) to represent substancesin order to see which bonds will break and form Bonds BREAKING Endothermic2) Sum the energies of ALL of the bonds that arebroken and subtract the sum of the energies ofALL of the bonds that are formed Bonds FORMING Exothermic Change in enthalpy (energy) for a reactioncan be found using the bond energies:3) Amounts of each substance (from the reactionequation) need to be considered when calculatingΔHrxn Σ(energies of bonds BROKEN) –Σ(energies of bonds FORMED)EX:Average Bond Energies 8193149208175347327253218266340393360452C CC CO OC OC ON ON NN NC NC N6148394957991074607418941615891Bond Enthalpy EXAMPLE:Calculate the change in enthalpy for the reactionusing bond energies.2 H2O2 è 2 H2O O2These arejust anAVERAGEfor each!Higher energy STRONGER bond!13
Bond Enthalpy EXAMPLE:Bond Enthalpy EXAMPLE:Calculate the change in enthalpy for the reactionusing bond energies.H2 CO2 è H2O COThe formation of ethyl butanoate, one of thecompounds that give pineapple its flavor, is producedaccording to the reaction below. Calculate the changein enthalpy for the reaction using bond energies.CO 2 H2 è CH3OHVSEPR TheoryValence Shell Electron Pair RepulsionValence electron pairs attempt to get as FARAPART as possible, thus changing the 3Dshape of the molecule!!!! Molecules are really 3D, not 2D Unshared (LONE) pairs are held closer to theatom and they repel other lone pairs and bondingpairs which pushes them closer togetherVSEPR TheoryValence Shell Electron Pair Repulsion Types of e- pairs:BONDING PAIRS è electrons that form the bondsLONE PAIRS è non-bonding electronsLONE PAIRS REPEL STRONGER THANBONDING PAIRS!!!Common Molecular Shapes LINEAR:Common Molecular Shapes LINEAR (another):BeH2XeF2Type: AB2180 bond angle2 atoms attached0 lone pairsType: AB2E3180 bond angle2 atoms attached3 lone pairs14
Common Molecular Shapes BENT:Common Molecular Shapes TRIGONAL PLANAR:H 2OBF3Type: AB2E2104.5 bond angle2 atoms attached2 lone pairs (or just 1)Common Molecular Shapes TRIGONAL PYRAMIDAL:NH3Type: AB3120 bond angle3 atoms attached0 lone pairsCommon Molecular Shapes T-SHAPED:ClF3Type: AB3E107.3 bond angle3 atoms attached1 lone pairCommon Molecular Shapes TETRAHEDRAL:Type: AB3E290 /180 bond angle3 atoms attached2 lone pairsCommon Molecular Shapes SEESAW:CH4SF4Type: AB4109.5 bond angle4 atoms attached0 lone pairsType: AB4E190 /120 /180 angles4 atoms attached1 lone pair15
Common Molecular Shapes SQUARE PLANAR:Common Molecular Shapes TRIGONAL BIPYRAMIDAL:XeF4PCl5Type: AB4E290 / 180 bond angle4 atoms attached2 lone pairsCommon Molecular Shapes SQUARE PYRAMIDAL:Type: AB590 /120 bond angle5 atoms attached0 lone pairsCommon Molecular Shapes OCTAHEDRAL:ClF5SF6Type: AB5E90 /180 bond angle5 atoms attached1 lone pairElectronic vs. MolecularType: AB690 bond angle6 atoms attached0 lone pairsElectronic vs. Molecular ELECTRONIC DOMAINS: based on theelectron groups on the central atom (ignoresshared vs. lone pairs) / helps with bond angle MOLECULAR GEOMETRY: used to describethe shape of the actual molecule EXAMPLE: H2O4 Electron Domains Tetrahedral ElectronGeometry! (4 attached)But, a Bent MolecularGeometry! (2 attachedand 2 lone pairs)16
Common Molecular Shapes*NOTE: Doubleor triple bondsin a moleculeoften give linearor planarshapes!!Orbital Hybridization TheoryCombines information about molecular bondingand molecular shape Pug Beagle s orbitalOrbital Hybridization Theory Lets look at CARBON: Puggle p orbitalsp orbital Orbital Hybridization Theory First thought was that carbon promoted one ofits 2s electrons to the empty 2p orbitalCan you see a problem with this?Carbon only has TWO electrons available forbonding That is not enough! Now try to bond to four hydrogen atoms to formmethane (CH4) So what’s going on here?Orbital Hybridization TheoryOrbital Hybridization Theory Measurements show that all four bonds areEQUAL so they must be HYBRIDIZED For methane, the s orbital combines with thethree p orbitals to create four equal sp3hybridized orbitals Three of the C-H bonds would involve a 2pmatched with a 1s, but a fourth bond would bebetween a 2s and a 1s This one bond would have slightly LESS energythan the other bonds in methane this is NOTwhat chemists observe though!2sp32sp32sp32sp31sNew orbitals have slightly MORE energy thanthe 2s and slightly LESS energy than the 2p!17
Orbital Hybridization TheoryOrbital Hybridization TheoryCombines information about molecular bondingand molecular shape Covalent bonds form when atomic orbitals overlap Mixing of s, p, and sometimes d orbitals thatallows bonds to form HYBRID ORBITALS Ex: BeF2Notice the energy is inbetween the 2s and 2p!Shape HybridizationssphybridizationMultiple Bond Hybridizations LINEAR (2 attached): sp TRIGONAL PLANAR (3 attached): sp2 TETRAHEDRAL (4 attached): sp3 TRIGONAL BIPYRIMIDAL (5 attached): sp3d OCTAHEDRAL (6 attached): sp3d2*EACH lone pair of e- counts asan “attached” group too!!Depends on which types oforbitals are being mixed!Sigma (σ) BondsElectrons are located around the central axisof a bondSingleBondsDoubleBondsTripleBonds(Just COUNTnumber of bondsto determine)sp2spPi (π) BondsElectrons are located above and below theaxis of a bond Single bonds Weaker than sigma bonds Ex: H2 Double bonds 1 sigma / 1 pi Triple bonds 1 sigma / 2 pi Ex: O2 / N218
Ionic Bonding EXAMPLE: Show the electron dot structures for calciumand phosphorususing arrows to indicate the transfer of e -. Ca2 P Ca PHOSPHORUS STILL NEEDS ONE MORE ELECTRON!!!! Ionic Bonding EXAMPLE: Show the electron dot structures for calciumand phosphorususing arrows to indicate the transfer of
Modern Chemistry 1 Chemical Bonding CHAPTER 6 Chemical Bonding SECTION 1 Introduction to Chemical Bonding OBJECTIVES 1. Define Chemical bond. 2. Explain why most atoms form chemical bonds. 3. Describe ionic and covalent bonding. 4. Explain why most chemical bonding is neither purely ionic or purley 5. Classify bonding type according to .
As bond order increases, bond length decreases, and bond energy increases H 2 bond order 1 A bond order of 1 corresponds to a single bond Bond order (number of-bonding e ) - (number of antibonding e ) 2 electrons/bond 38 MO Energy Diagram for He 2 Four electrons, so both and *
Metallic Bonding Metallic Bonding The metallic bond consists of positively charged metallic cations that donate electrons to the sea. The sea of electrons are shared by all atoms and can move throughout the structure. Metallic Bonding Metallic Bonding In a metallic bond: – The resulting bond is a cross between covalent and ionic .
4.2 Covalent Bonding 4.3 Shapes of Molecules 4.4 Electronegativity, Bond Polarity, Bond Length and Bond Energy 4.5 Intermolecular Forces 4.6 Metallic Bonding 4.7 Bonding and Physical Properties of Substances Learning outcomes: (a) describe ionic (electrovalent) bonding, as in sodium chloride and magnesium oxide, including
comparing with Au wire bonding. Bonding force for 1st bond is the same range, but approx. 30% higher at 2nd bonding for both Bare Cu and Cu/Pd wire bonding but slightly lower force for Bare Cu wire. Bonding capillary is PECO granular type and it has changed every time when new cell is used for bonding
Examples: Bonding in H2 (simplest example) H: 1s1 H H Hi l b d HHH H 2: -H single bond – How does this bonding occur? What do the individual H atoms "see" as they approach one another? – Bond formed results from the overlap of a single orbital from each atom: sigma bond ( bond) Bonding
MERRYLAND HIGH SCHOOL ENTEBBE S.2 CHEMISTRY NOTES BONDING AND STRUCTURE NOTES BONDING Bonding is the chemical combination of atoms or elements to form compounds. The force of attraction holding atoms or elements together in a molecule/crystal is referred to as a chemical bond. Chemical bonding /combination occurs mainly in four forms
Pure covalent bonding only occurs when two nonmetal atoms of the same kind bind to each other. When two different nonmetal atoms are bonded or a nonmetal and a metal are bonded, then the bond is a mixture of cova-lent and ionic bonding called polar covalent bonding. Covalent Bonding In METALLIC BONDING the valence electrons are
