7Electrons that form the second C-O bond in the double bonds below do not always sit between that C and that OThey move among the two oxygens and the carbon.
8Exceptions to the Octet Rule Three situations with exceptions to the octet rule:When Ions or molecules have:an odd number of electronsless than an octet (B & Al)more than eight valence electrons (an expanded octet)
9Exceptions!Boron and Aluminum are okay with only 6 e- around themBF3
10More Than an OctetPCl5 can only exist is if phosphorus has 10 electrons around it.Presumably d orbitals in these atoms participate in bonding.
11Different Bond Types Ionic (extremely polar) Covalent Electrons are transferredCovalentPolar – uneven sharing of electronsNonpolar – even sharing of electrons
15ElectronegativityElectronegativity is the ability of atoms in a molecule to attract electrons to themselves.On the PT, EN increases:…from left to right across a row.EN decreases…from the top to bottom of a group (column).
17Bond properties and electronegativity Any bond can be classified by subtracting the EN of the 2 elements involvedHigh differences in electronegativity (1.7 – 4) make the bond IONICLow differences (0-1.7) make the bond COVALENT:Polar covalent – 0.4 – 1.7Nonpolar Covalent – 0 – 0.4
18Polar Covalent BondsElectrons are not always shared equally in compounds.Oxygen pulls harder on the electrons it shares with hydrogen than hydrogen does.Oxygen’s end of the molecule has more electron density than the hydrogen end.
19Nonpolar, polar, and ionic bonds (a) – a nonpolar covalent bond(b) – a polar covalent bond(c) – an ionic bond
20Polar Covalent BondsWhen two atoms share electrons unequally, a bond dipole results.
21Polar Covalent BondsThe greater the difference in electronegativity, the more polar is the bond.