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Chemical Bonding. Chapter 8 Polarity and Dipole moments. Review. Order the following bonds according to polarity: H-H, O-H, Cl-H, S-H, and F-H. H-H S-H Cl-H O-H F-H. Bond Polarity and Dipole Moments.

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chemical bonding

Chemical Bonding

Chapter 8

Polarity and Dipole moments

review
Review
  • Order the following bonds according to polarity: H-H, O-H, Cl-H, S-H, and F-H.
  • H-H
  • S-H
  • Cl-H
  • O-H
  • F-H
bond polarity and dipole moments
Bond Polarity and Dipole Moments
  • Molecules with a charge distribution of a positive end and a negative end are dipolar, or said to have a dipole moment.
  • But what about molecules made up of more than one atom?
polar molecules are not always dipoles
Polar molecules are not always dipoles
  • In a linear molecule such as carbon dioxide, the individual bond polarities are arranged in such a way that they cancel each other out.
  • Water is a bent molecule with a permanent dipole.
electron configurations
Electron Configurations
  • Electron arrangement helps us to understand configurations of compounds.
  • In stable compounds, virtually every atom has a noble gas type arrangement of electrons.
generalizations of electrons in stable compounds
Generalizations of electrons in stable compounds
  • Two non-metals react to form covalent bonds in a way that completes the valence electron configuration of both atoms.
  • A metal and a non-metal react to form a binary ionic compound. The ions form to achieve the electron configuration of the nearest noble gas.
predicting formation of ions
Predicting formation of ions
  • When discussing ionic compounds, scientists are generally referring to ions in their solid state, not gaseous state.
predicting ions continued
Predicting ions continued
  • Atoms lose or gain electrons to imitate the nearest noble gas. This gain or loss of electrons results in a charged atom called an ion.
  • Ions are attracted to oppositely charged ions and bond to form neutral compounds
exceptions
Exceptions
  • Elements in Group 1A lose an electron.
  • Elements in Group 2A lose 2 electrons.
  • Elements in Group 7A gain an electron.
  • Elements in Group 6A gain 2 electrons, etc.
  • But…elements Sn may lose 2 or 4 electrons.
  • Pb2+ or Pb4+, Bi 3+ or Bi5+, Cu1+ or Cu2+ and so on.
size and charge
Size and Charge
  • Ion size is important in determining the structure and stability of ionic solids.
  • What determines the Size?
  • Look first at relative size of ion and its parent atom.
ion size
Ion Size
  • Positively charge ions have lost outer shell electrons and are smaller than their parent atom.
  • Negatively charged ions have gained electrons and are larger than their parent atom.
isoelectronic ions
Isoelectronic ions
  • These are ions of different elements with the same number of electrons.
  • For example O2-, F-, Na+, Mg2+ and Al3+
  • All have the Electron configuration of Neon.
  • What is Z?
examples
Arrange the ions in order of decreasing size.

Se2-, Br-, Rb+ and Sr2+

Se2-

Br-

Rb+

Sr2+

Choose the largest in each group.

Li+, Na+, K+, Rb+, Cs+

Answer: Cs+

Ba2+, Cs+, I-, Te2-

Te2-

Examples