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The Halogens

41. The Halogens. 41.1 Characteristic Properties of the Halogens 41.2 Variation in Properties of the Halogens 41.3 Comparative Study of the Reactions of Halide Ions 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride. 41.1.

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The Halogens

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  1. 41 The Halogens 41.1 Characteristic Properties of the Halogens 41.2 Variation in Properties of the Halogens 41.3 Comparative Study of the Reactions of Halide Ions 41.4 Acidic Properties of Hydrogen Halides and the Anomalous Behaviour of Hydrogen Fluoride

  2. 41.1 Characteristic Properties of the Halogens

  3. 41.1 Characteristic Properties of the Halogens (SB p.78) Introduction • Group VIIA elements include • fluorine • chlorine • bromine • iodine • astatine

  4. 41.1 Characteristic Properties of the Halogens (SB p.78) Introduction • Astatine •  not much is known • radioactive

  5. 41.1 Characteristic Properties of the Halogens (SB p.78) Introduction • Group VIIA elements •  also called halogens

  6. 41.1 Characteristic Properties of the Halogens (SB p.78) The halogens

  7. 41.1 Characteristic Properties of the Halogens (SB p.79) Introduction • All halogens •  outermost shell electronic configuration of ns2np5 • one electron short of the octet electronic configuration

  8. 41.1 Characteristic Properties of the Halogens (SB p.79) Introduction • In the free elemental state •  form diatomic molecules •  complete their octets by sharing their single unpaired p electrons

  9. 41.1 Characteristic Properties of the Halogens (SB p.79) Introduction • When halogens react with other elements •  complete their octets •  depending on the electronegativity of the element

  10. 41.1 Characteristic Properties of the Halogens (SB p.79) Introduction • Either • gaining an additional electron to form halide ions •  or sharing their single unpaired p electrons to form single covalent bonds

  11. 41.1 Characteristic Properties of the Halogens (SB p.79) Appearances of halogens at room temperature and pressure: chlorine chlorine

  12. 41.1 Characteristic Properties of the Halogens (SB p.79) bromine Appearances of halogens at room temperature and pressure: bromine

  13. 41.1 Characteristic Properties of the Halogens (SB p.79) iodine Appearances of halogens at room temperature and pressure: iodine

  14. 41.1 Characteristic Properties of the Halogens (SB p.79) High Electronegativity Electronegativity is the relative tendency of an atom to attract bonding electrons towards itself in a covalent bond.

  15. 41.1 Characteristic Properties of the Halogens (SB p.79) High Electronegativity • All halogens • high electronegativity values • high tendency to attract an additional electron to achieve the stable octet electronic configuration •  highest among the elements in the same period

  16. 41.1 Characteristic Properties of the Halogens (SB p.79) Electronegativity values of halogens

  17. 41.1 Characteristic Properties of the Halogens (SB p.79) High Electron Affinity Electron affinity is the enthalpy change when one mole of electrons is added to one mole of atoms or ions in the gaseous state.

  18. 41.1 Characteristic Properties of the Halogens (SB p.79) High Electron Affinity • Its value •  indicates the ease of formation of anions

  19. 41.1 Characteristic Properties of the Halogens (SB p.79) High Electron Affinity • All halogens •  negative values of electron affinity •  high tendency to attract an additional electron to form the respective halide ions

  20. 41.1 Characteristic Properties of the Halogens (SB p.79) Electron affinities of halogens

  21. 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State • Halogens • gain an additional electron to form the halide ions • combine with metals to form metal halides • held together by ionic bonding

  22. 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State • The oxidation states of the halogens = –1

  23. 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State • The halogen atoms • share their unpaired p electrons with a non-metallic atom • form a covalent bond

  24. 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State • Halogens (except fluorine) • exhibit an oxidation state of –1 or +1 in the covalent molecules formed • depend on the electronegativity of the elements that are covalently bonded with the halogens

  25. 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State • All halogens (except fluorine) • can expand their octets of electrons by utilizing the vacant, low-lying d orbitals

  26. 41.1 Characteristic Properties of the Halogens (SB p.80) Bonding and Oxidation State • Each of these halogen atoms • have variable numbers of unpaired electrons to pair up with electrons from other atoms • able to form compounds of different oxidation states

  27. 41.1 Characteristic Properties of the Halogens (SB p.80) “Electrons-in-boxes” diagrams of the electronic configuration of a halogen atom of the ground state and various excited states

  28. 41.1 Characteristic Properties of the Halogens (SB p.81) Various oxidation states of halogens in their ions or compounds

  29. 41.1 Characteristic Properties of the Halogens (SB p.81) Various oxidation states of halogens in their ions or compounds

  30. 41.1 Characteristic Properties of the Halogens (SB p.81) Bonding and Oxidation State • Fluorine • cannot expand its octet •  no low-lying empty d orbitals available •  the energy required to promote electrons into the third quantum shell is very high

  31. 41.1 Characteristic Properties of the Halogens (SB p.81) Bonding and Oxidation State • Fluorine • the most electronegative element • only one unpaired p electron available for bonding • oxidation state is limited to –1

  32. 41.1 Characteristic Properties of the Halogens (SB p.82) Colour • All halogens • coloured •  the absorption of radiation in the visible light region of the electromagnetic spectrum

  33. 41.1 Characteristic Properties of the Halogens (SB p.82) Colour • The absorbed radiation • the excitation of electrons to higher energy levels

  34. 41.1 Characteristic Properties of the Halogens (SB p.82) Colour • Fluorine atom •  smaller size • absorb the radiation of relatively high frequency (i.e. blue light) • appears yellow

  35. 41.1 Characteristic Properties of the Halogens (SB p.82) Colour • Atoms of other halogens •  larger sizes • absorb radiation of lower frequency

  36. Let's Think 1 41.1 Characteristic Properties of the Halogens (SB p.82) Colour • Iodine • absorbs the radiation of relatively low frequency (i.e. yellow light) • appears violet

  37. 41.1 Characteristic Properties of the Halogens (SB p.82) Colour • Halogens •  different colours when dissolved in different solvents

  38. 41.1 Characteristic Properties of the Halogens (SB p.82) Colour • Halogens •  non-polar molecules •  not very soluble in polar solvents (such as water) • but very soluble in organic solvents (such as 1,1,1-trichloroethane)

  39. 41.1 Characteristic Properties of the Halogens (SB p.82) Colours of halogens in pure form and in solutions

  40. 41.1 Characteristic Properties of the Halogens (SB p.82) (b) (c) (a) Colours of halogens in water:(a) chlorine; (b) bromine; (c) iodine

  41. 41.1 Characteristic Properties of the Halogens (SB p.83) (a) (b) (c) Colours of halogens in 1,1,1-trichloroethane:(a) chlorine; (b) bromine; (c) iodine

  42. Check Point 41-1 41.1 Characteristic Properties of the Halogens (SB p.83)

  43. 41.2 Variation in Properties of the Halogens (SB p.83) Introduction • All halogens • exist as diatomic molecules

  44. 41.2 Variation in Properties of the Halogens (SB p.83) Introduction • In the diatomic molecules • the halogen atoms are held together by strong covalent bonds

  45. 41.2 Variation in Properties of the Halogens (SB p.83) Introduction • The molecules • only held together by weak van der Waals’ forces (i.e. instantaneous dipole-induced dipole interaction)

  46. 41.2 Variation in Properties of the Halogens (SB p.83) Introduction • The physical properties of halogens • strongly affected by the way that the atoms are joined together • the interactions that hold the molecules together

  47. 41.2 Variation in Properties of the Halogens (SB p.83) Some physical properties of the halogens

  48. 41.2 Variation in Properties of the Halogens (SB p.83) Some physical properties of the halogens

  49. 41.2 Variation in Properties of the Halogens (SB p.84) Variation in Physical Properties 1. Melting Point and Boiling Point • Halogens • exist as non-polar diatomic molecules

  50. 41.2 Variation in Properties of the Halogens (SB p.84) 1. Melting Point and Boiling Point • Going down the group • the melting points and boiling points of halogens increase

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