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January 4, 2011 Objectives Define molecule

January 4, 2011 Objectives Define molecule Discuss the relationship of the physical and chemical properties of the molecules to the properties of the atoms from which they are made (They’re different!) Explain what covalent bonds are and why they are formed.

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January 4, 2011 Objectives Define molecule

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  1. January 4, 2011 Objectives Define molecule Discuss the relationship of the physical and chemical properties of the molecules to the properties of the atoms from which they are made (They’re different!) Explain what covalent bonds are and why they are formed. Draw a Lewis Dot diagram for any covelent molecule, indicating the number of valence electrons on each atom in the diagram.

  2. What holds molecules together?

  3. Molecule: collection of atoms that are bound together

  4. What is a covalent bond? • What holds a molecule together? Covalent bond • Force of attraction that results from valence electrons being attracted to two nuclei. • Valence electrons being shared between two nuclei • Core electrons are not involved in bonding • Valence electrons are shared between the two nuclei

  5. Ways to represent shared electrons H:H H..H H-H

  6. Covalent Bonds are very strong!

  7. Bond formation always releases energy

  8. How many valence electrons does each molecule have?

  9. Why won’t two Helium atoms form a molecule?

  10. What do all elements want to be like? Why?

  11. The Octet Rule • Remember for the representative elements the Roman Numeral group number tells you the number of valence electrons. • He is the only exception. Why? • Formula for Water and Methane.

  12. Practice • What is the formula for ammonia? • What is the formula for carbon and chlorine?

  13. The Lewis Dot Diagram

  14. Lewis Dot diagrams • Show an atom’s valence electrons • The number of dots is equal to the group number • Pairs of dots(electrons) are electron pairs • Single electrons are unpaired electrons

  15. I II III IV V VI VII VIII Transition metals Metalloids Nonmetals Metal

  16. Non Metals and The Dots

  17. Electron Pairs vs. Unpaired Electron

  18. Bonding Pairs vs. Lone Pairs

  19. Steps to drawing dot diagrams • Count up how many valence electrons will be in the final diagram (PCl3) (CO) • Connect the atoms with single bonds. Assume first non hydrogen atom is the central atom (PCl3) • Put the remaining dots in as lone pairs. First on the terminal atoms then on the central atom. Don’t use more electrons then you have.

  20. Steps to drawing dot diagrams • (CO ) Remember every atom needs an octet. Lone pairs to the rescue. Only from adjacent atoms.

  21. Multiple Covalent Bonds O2 N2

  22. Multiple Covalent Bonds CO2 C2H2

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