Shapes of molecules IlTHEEXAMPLESBELOWSHOWTHEPROCESSINACTION:CO2StepsCOg-SO3SO-MnOASO2-1NoneNone2-0-2-0-1-0-2-0-.C23=0O2-03=04=2福.O603O=C=0MO0=C=04?ODlinearplanarplanartrigonaltetrahedraltetrahedraltrigonaltrigonalpyramidal16
16 Shapes of molecules II
Shapes of molecules IIDELOCALIZATIONThe structure of the carbonate anion shows two single bonds andone double bond.In fact experimental data show that all thebonds in the carbonate ion are the same lengthand allthe bondangles are the same. They are longer than a C=O bond butshorter than a C-O bond. This shows that the bonding model wehave used is wrong and in fact the π bond has been delocalizedthroughout the molecule.The charge has also been spread overthe whole molecule rather than being concentrated on only two ofthe oxygens.Delocalization occurs inmost oxo-anions (e.g)gbondoverlapofporbitalsnitrate,sulfate,ethanoate.throughout the particlemanganate,etc.)andinsome organic moleculessuch as benzene.元overlap
17 Shapes of molecules II The structure of the carbonate anion shows two single bonds and one double bond. In fact experimental data show that all the bonds in the carbonate ion are the same length and all the bond angles are the same. They are longer than a C=O bond but shorter than a C-O bond. This shows that the bonding model we have used is wrong and in fact the p bond has been delocalized throughout the molecule. The charge has also been spread over the whole molecule rather than being concentrated on only two of the oxygens. Delocalization occurs in most oxo-anions (e.g. nitrate, sulfate, ethanoate, manganate, etc.) and in some organic molecules such as benzene. DELOCALIZATION
Shapes of molecules IIWordsWordsX-ray diffraction (XRD)oxo-compound;oxo-anionminus charged;plus charged(negatively charged; positively charged)nitrate;carbonate;sulphatebenzene18
18 Shapes of molecules II Words Words X-ray diffraction (XRD) oxo-compound; oxo-anion minus charged; plus charged (negatively charged; positively charged) nitrate; carbonate; sulphate benzene
Charge separation and dipole momentsELECTRONEGATIVITYDIFFERENCEANDCHARGESEPARATION:THEUNEVENSHARINGOEELECTRONSIf the twoatoms at each end of abond are the same, then theelectrons will be equally sharedOOX910HOH8CCI交00but if they are different their attraction for the shared pair willbe different.The difference in attraction is found by looking atthe difference in electronegativity of the two atoms. Theelectrons will be pulled nearer the atom with the biggerelectronegativity. That atom will become slightly negativelycharged, shown diagrammatically as -, and the other atomwith the smaller electronegativity will become slightly positivelycharged, shown as S+19
19 Charge separation and dipole moments If the two atoms at each end of a bond are the same, then the electrons will be equally shared ELECTRONEGATIVITY DIFFERENCE AND CHARGE SEPARATION: THE UNEVEN SHARING OF ELECTRONS but if they are different their attraction for the shared pair will be different. The difference in attraction is found by looking at the difference in electronegativity of the two atoms. The electrons will be pulled nearer the atom with the bigger electronegativity. That atom will become slightly negatively charged, shown diagrammatically as d-, and the other atom with the smaller electronegativity will become slightly positively charged, shown as d+
Charge separation anddipole momentsThis process is called charge separation. A bond along which thecharge has been separated into positive and negative parts iscalled a polar bond and has a dipole.This means that there aretwo separated regions of charge.2.53.02.1xxXS福大H洛C3.580x83.5XX0000SdA20
20 Charge separation and dipole moments This process is called charge separation. A bond along which the charge has been separated into positive and negative parts is called a polar bond and has a dipole. This means that there are two separated regions of charge