Ch 3 Lecture 2 Bonding ConsiderationsI. VSEPR Theory ContinuedA. Lone Pair Repulsion! Lone pairs are as i"portant as ato"s in VSEPR2! Irregular structures result #hen central ato"s ha$e lone pairs3! Lone pairs %lp! occupy "ore space on the central ato" than &onding pairs %&p!a. &p electrons are attracted to a second nucleus&. lp electrons are locali'ed on the central ato"c. %lp(&p! repulsion is greater than %&p(&p! repulsiond. A""onia )(*() &ond angle + ,-.-o instead o. ,/.0o e. 1ater )(2() &ond angle + ,3.0o instead o. ,/.0o B. Su&tle 4eo"etric In.luences. Si'e o. the central ato" a. Larger central ato" leads to longer &onds and less &p(&p repulsion&. S"aller &ond angles resultc. E5a"ple6)227 )2S7 )2Se7 )2Te2. Electronegati$ity o. outer ato"sa. 8ore electronegati$e outer ato" pulls &p to#ards it&. Reduces &p(&p repulsion and "a9es s"aller &ond anglesc. E5a"ple6 P:37 PCl37 PBr37 PI3

3. Si'e o. outer ato"sa. Very s"all outer ato"s %)! "ay re$erse e5pected trends&. E5a"ple6 S)27 S:27 SCl2 3. E5act predictions are rarely needed7 ;ualitati$e predictions are o.ten enough.0. Ta&le 3linear&ent&enttrigonal pyra"idsee ! %2! % ! %! % ! %2! % ! %! % ! %=++ = + + = + = -. Large di..erences gi$e ionic &ondsF s"all di..erences gi$e polar co$alent &onds>. Actual $alues co"e .ro" a$eraging se$eral co"pounds o. the ato" to re"o$e e5peri"ental errorE. Actual $alues in a gi$en "olecule "ay $ary .ro" the a$erage/. *o&le gases ha$e high $alues &ecause o. high e..ecti$e nuclear chargesa. S"all si'e&. Large ? nucleusIII. Polar BondsA. Any &ond &et#een ato"s o. di..erent electronegati$ities is polar! Electrons concentrate on one side o. the &ond2! 2ne end o. the "olecule is %?! and one end is %! &ecause o. $ariation lengths and angles&. Lone pairs ha$e a large in.luence on dipole "o"ent as #ellA B