ThechemicalcontextoflifeSummary2.1Matterconsistsofchemicalelementsinpureformandincombinationscalledcompounds•Elementscannotbebrokendownchemicallytoothersubstances.•Acompoundcontainstwoormoredifferentelementsinafixedratio.•Oxygen,carbon,hydrogen,andnitrogenmakeupapproximately96%oflivingmatter.Summary2.2Anelement’spropertiesdependonthestructureofitsatoms•Anatom,thesmallestunitofanelement,hasthefollowingcomponents:•Anelectricallyneutralatomhasequalnumbersofelectronsandprotons;thenumberofprotonsdeterminestheatomicnumber.•Theatomicmassismeasuredindaltonsandisroughlyequaltothesumofprotonsplusneutrons.•Isotopesofanelementdifferfromeachotherinneutronnumberandthereforemass.•Unstableisotopesgiveoffparticlesandenergyasradioactivity.•Inanatom,electronsoccupyspecificelectronshells;theelectronsinashellhaveacharacteristicenergylevel.•Electrondistributioninshellsdeterminesthechemicalbehaviorofanatom.•Anatomthathasanincompleteoutershell,thevalenceshell,isreactive.•Electronsexistinorbitals,threedimensionalspaceswithspecificshapesthatarecomponentsofelectronshells.Summary2.3Theformationandfunctionofmoleculesdependonchemicalbondingbetweenatoms•Chemicalbondsformwhenatomsinteractandcompletetheirvalenceshells.Covalentbondsformwhenpairsofelectronsareshared.•Moleculesconsistoftwoormorecovalentlybondedatoms.•Theattractionofanatomfortheelectronsofacovalentbondisitselectronegativity.•Ifbothatomsarethesame,theyhavethesameelectronegativityandshareanonpolarcovalentbond.•Electronsofapolarcovalentbondarepulledclosertothemoreelectronegativeatom.•Anionformswhenanatomormoleculegainsorlosesanelectronandbecomescharged.•Anionicbondistheattractionbetweentwooppositelychargedions.•Weakbondsreinforcetheshapesoflargemoleculesandhelpmoleculesadheretoeachother.•Ahydrogenbondisanattractionbetweenahydrogenatomcarryingapartialpositive•charge(δ+)andanelectronegativeatom(δ-).•VanderWaalsinteractionsoccurbetweentransientlypositiveandnegativeregionsofmolecules.Summary2.4Chemicalreactionsmak...
