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Chemical Bonding

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

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  1. Chemical Bonding Chapter 8 Polarity and Dipole moments

  2. 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

  3. 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?

  4. 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.

  5. Other molecules with polar bonds but no dipole.

  6. 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.

  7. 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.

  8. Predicting formation of ions • When discussing ionic compounds, scientists are generally referring to ions in their solid state, not gaseous state.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. Ion Size

  14. 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?

  15. 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

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