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Chemical Bonding

This chapter reviews the concept of bond polarity and dipole moments in chemical bonding. It discusses the order of polarity for different bonds and explains the difference between polar molecules and dipoles. The chapter also covers electron configurations, predicting ion formation, and the relationship between ion size and charge.

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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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