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Starter. For each ion, draw a dot-and-cross diagram and predict the shape and bond angles. H 3 O + NH 2 -. Electronegativity and polarity. L.O.: Describe electronegativity in terms of an atom attracting bonding electrons in a covalent bond.

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  1. Starter For each ion, draw a dot-and-cross diagram and predict the shape and bond angles. • H3O+ • NH2-

  2. Electronegativity and polarity L.O.: Describe electronegativity in terms of an atom attracting bonding electrons in a covalent bond. Explain how a permanent dipole can result in a polar bond.

  3. Electron density describes the way negative charge is distributed in a molecule. Where is the electron density in the H-O? Which atom has the most electron-pulling power?

  4. Electronegativity is a measure of the attraction of a bonded atom for the pair of electrons in a covalent bond

  5. Factors affecting electronegativity 1) Nuclear charge – the more protons, the stronger the attraction from the nucleus to the bonding pair of electrons. 2) Atomic radius – the closer the bonding electrons to the nucleus, the stronger the attraction from the nucleus to the bonding pair of electrons. 3)Shielding – the less shells of electrons shielding (repelling) the bonding electrons, the stronger the attraction from the nucleus to the bonding pair of electrons.

  6. Trend down a group Electronegativity decreases • Atomic radius increases • More shielding •  Less attraction between nucleus and bonding pair of electrons

  7. Trend across a period Electronegativity increases • Atomic radius decreases • More nuclear charge •  Stronger attraction between nucleus and bonding pair of electrons

  8. Bonds like this are polar. The greater the difference in polarity, the more polar is the covalent bond

  9. A permanent dipole is a small charge difference across a bond that results from a difference in the electronegativities of the bonded atoms. A polar covalent bond has a permanent dipole.

  10. http://chemsite.lsrhs.net/ChemicalBonds/images/custom_dipole2.swfhttp://chemsite.lsrhs.net/ChemicalBonds/images/custom_dipole2.swf

  11. Why is fluorine more electronegative than chlorine? Fluorine is a smaller atom and when it forms a covalent bond, the shared electrons are closer to the nucleus.

  12. Pauling electronegativity values across the Periodic Table

  13. CCl4 is a non-polar molecule CCl4 is symmetrical. The dipoles act in different directions and cancel each other out. CCl4 is a non-polar molecule with polar bonds.

  14. Range of bonding from covalent to ionic

  15. Arrange the following covalent bonds in order of increasing polarity: H-O, H-F, H-N. • The order of polarity is the same as the order of electronegativity of the second atom.

  16. Write + and - signs to show the polarity of the bonds in a hydrogen chloride molecule

  17. Group these molecules into polar and non-polar. Draw their shapes and show dipoles: CO2 Cl2 NH3 PF3 BF3 H2O CH4

  18. Electronegativity and polarity L.O.: Describe electronegativity in terms of an atom attracting bonding electrons in a covalent bond. Explain how a permanent dipole can result in a polar bond.

  19. Non-polar bond Polar bond

  20. Electronegativity Difference 0 4 - + X- X Y X Y X- Y+ Y+ Pure covalent Polar ionic Distorted ions Pure ionic Polar covalent Electrons not equally shared Polarisation of covalent bonds Polarisation of ions Favoured by small, highly charged +ve ions, e.g. Li+, Be2+

  21. Covalent bonding Ionic bonding

  22. Difference in electronegativity decreases +ve ion gets smaller and more highly charged, so –ve polarised more

  23. Difference in electronegativity decreases +ve ion gets smaller and more highly charged, so –ve polarised more

  24. H2O - O H H + + Bonds: polar Molecule: polar

  25. NH3 - N H H H + + + Bonds: polar Molecule: polar

  26. CO2 - + - O C O Bonds: polar Molecule: non-polar

  27. - Cl + C Cl Cl Cl - - - CCl4 Bonds: polar Molecule: non-polar

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