Chapter 12

Chemical BondsChapter 12Types of BondsIonic bond: one that holds an ionic cmpd togetherRelatively strongResults in high melting/boiling pointsCovalent bond: one that holds a covalent cmpd togetherNot as strongLower melting/boiling points2 types: polar covalent and nonpolar covalent

In an ionic cmpd, the anion is always larger while the cation fits within the gaps of the anions making a strong crystal lattice.

Polar Covalent BondsType of covalent bond Electrons are shared unequallyOne element has a high affinity for gaining the electron thus forming a slight and the other element is slightly +

Nonpolar Covalent BondsType of covalent bond Electrons are shared equallyUsually occurs between 2 identical elements or symmetrical molecules

ElectronegativityEN-ability of an atom in a molecule to attract shared electrons to itselfCan help determine the type of bond as wellGenerally a difference of 0=nonpolar covalent bond, 0.1-2.0-polar covalent bond, above 2.0=ionic bond

Dipole MovementsAll polar molecules have a dipole movementDipole movement-something that exhibits a + and chargeAn arrow represents the direction of the dipole movementThe more EN element has the arrow side and the least EN has a plus end

Waters polarity is what allows water to attract both + and ions, allowing many things to dissolve in water.Also causes water molecules to adhere to each other strongly (reason why a lot of energy is needed to evaporate water)

ExamplesPage 404 Ex. 12.1Page 406 # 4 and 6Lewis StructuresA representation that shows how valence electrons bond.Hydrogen is the only element that follows the duet rule-needs 2 electrons to be stableOther elements follow the octet rule-need 8 electrons to be stableBonding electrons-those involved in bondingLone pair electrons-those not involved in bondingExamplesH2H2OPH3CCl4

Multiple BondsSingle bond-sharing of 2 electronsDouble bond-sharing of 4 electronsTriple bond-sharing of 6 electronsEx: HCN

Resonance & Formal ChargeSome elements exhibit multiple Lewis structures like carbon dioxide. See if you can draw all 3.Resonance structures-when more than 1 valid Lewis Structure can be drawnUse arrows to show resonanceHow do we know which is right? Want the formal charge on all elements to be as close to zero as possible# of valence nonbonding (bonding / 2)

Some resonance structures will not require formal charge as they are mirror images of each otherEx: ozone(O3), SO3What is the formal charge on each element in the above?Polyatomic IonsAdd/subtract electrons as neededPut the structure in brackets with the charge outsideCheck for resonanceEx: NO2 -1, CO3-2 Exceptions to the ruleBoron is happy with 6 electronsAnything to the right and below phosphorus can technically have expanded octets. We will work mostly with phosphorus and sulfur. Ex: BF3, SF6, PCl5

Molecular Structure3D arrangement of the valence electrons (both bonded and non)VSEPR theory-valence shell electron pair repulsion theoryThe structure around a given atom is determined by minimizing repulsions between electrons pairs.AKA: electrons spread out as far away from each other as possibleElectron pair geometry vs. molecular geometry Electron pair includes all electrons including bonded and nonMolecular refers only to the bonding electrons

http://intro.chem.okstate.edu/1314f00/lecture/chapter10/vsepr.htmlMain types/Subtypes with bond anglesLinear- 180Trigonal Planar -120Bent- under 118Tetrahedral- 109.5Trigonal pyramidal- 107Bent- 105Trigonal bipyramidal- 90,120,180Octahedral- 90Square Planar- 90

Linear-ElectronLinear-MolecularEX: CO2Bond angle of 180

Trigonal Planar-ElectronTrigonal Planar-MolecularEx: BF3Bond angle of 120 Bent-MolecularOzoneBond angle of 118

23Tetrahedral-ElectronTetrahedral-molecularEx: Methane, CH4Bond angles of 109.5 Trigonal Pyramidal-molecularEx: NH3Bond angle of 107 Bent-molecularEx: WaterBond angle of 105

Trigonal Bipyramidal-ElectronTrigonal bipyramidal-molecularEx: PCl5Bond angles of 90, 120, 180

Octahedral-ElectronOctahedral-molecularEx: SF6Bond angle of 90Square planar-molecularEx: XeF4Bond angle of 90

In-Class Practice Provide bond angles for allPage 429 honors book Ex. 12.6Others: nitrite ion, sulfur trioxide, phosphorus pentafluoride, SiF6-2