CHEMICAL BONDING

1. CHEMICAL BONDING Chapter: 7-8

2. Do Now #1 How do you find the number of valence electrons in an atom of a representative element (s & p block)? # of e- on outer most energy level, group # from PT Draw the electron dot structure for chlorine.

3. Do Now #2 Draw the lewis structure for aluminum sulfide. Al2S3

4. DO NOW: PAGE – 6 of your NOTES pkt TRY: Label the substances below as: metallic, ionic, network covalent, molecular (non-polar) or molecular (polar). a. dissolves in water, does not conduct electricity as a solid, but does when dissolved in water b. dissolves in acetone, low boiling point c. shiny, conducts electricity as a solid d. gas at room temperature e. NH3 f. NaBr g. CO2 IONIC NON-POLAR METALLIC NON-POLAR POLAR IONIC NON-POLAR

5. TRY Identify each substance below as: ionic, metallic, network covalent, polar covalent or nonpolar covalent. Then arrange the substances in order of increasing (lowest to highest) melting point. P NP I Net M Melting point: _________ < _________ < _________ < ________ < __________ CO2 CH2O Fe KF SiO2

6. TRY:Compare and contrast Molecular and Ionic Compounds using water and sodium chloride as an example. Water, which is a molecular compound, and sodium chloride, which is an ionic compound (Formula unit), are compared here. Array of sodium ions and chloride ions Collection of water molecules Formula unit of sodium chloride Molecule of water NaCl Chemical formula Chemical formula H2O

7. TYPES OF BONDING AND PROPERTIES IONIC BONDING • Metal + monoatomic ion • Metal + polyatomic ion • Positive ion + negative ion Ionic bonds-intramolecular

8. Transfer of e- CaCl2 Opposite charges attract “formula unit” AlF3

9. PROPERTIES OF IONIC COMPOUNDS • SOLID at room temperature • Has a “Crystal” Structure • High melting & boiling points

10. PROPERTIES OF IONIC COMPOUNDS What is needed to conduct electricity? Charged particles that can move • Does NOT conduct electricity (solid state) • CAN conduct electricity when dissolved in water & molten

11. Power source Current meter Flow of electrons Flow of electrons Inert metal electrodes Cl– Na+ To (+) electrode To (–) electrode When sodium chloride is melted, the orderly crystal structure breaks down. • If a voltage is applied across this molten mass, cations migrate freely to one electrode and anions migrate to the other. • This movement of electrons allows electric current to flow between the electrodes through an external wire.

12. METALLIC BONDING: Metals only! • Metallic bonds: the forces of attraction between the free-floating valence electrons and the positively charged metal ions. (intramolecular forces) Positive metal ions in fixed positions Mobile Valence electrons delocalized electrons - “sea” of mobile electrons

13. Gold PROPERTIES OF METALS • Solid at room temperature (EXCEPT MERCURY) • Has a “Crystal” Structure • Shiny (luster) • Good conductors of electric current & heat electrons can flow freely

14. Force Metal rod Wire PROPERTIES OF METALS • Ductile (can be drawn into wires) Force Sea of e- Metal cation • Malleable (can be hammered or pressed into shapes)

15. What is a “network covalent substance?” In regular covalent substances, we see separate molecules. Network covalent substances: atoms are covalently bonded with each other WITHOUT ever forming separate molecules. Instead, the bonds extend throughout the entire solid like one giant molecule. THESE ARE THE STRONGEST COMPOUNDS!!!!

16. PROPERTIES OF NETWORK COVALENT BONDING • VERY high boiling and melting points • Solid at room temperature • Has a “Crystal” Structure • Non-conducting

17. Why doesn’t oil dissolve in water?

18. COVALENT MOLECULES : POLAR VS. NON-POLAR (pg-6) POLAR (between molecules - dispersion & dipole forces) NON-POLAR (between molecules - dispersion forces only) The Rule Is “Like Dissolves Like” intermolecular forces of the molecules easily match

19. NONPOLAR COVALENT Molecules w/ shared e- where atoms around the center ARE the same. Properties: • Dissolves in acetone & gasoline • Low MP & BP • Non conductors • S, l or g depends on mass Attracted by Dispersion forces:caused by the motion of electrons (weakest)

20. Dispersion Forces (temporary dipole or induced dipole) Non-polar molecules in which the ends of the molecules are not charged, are not attracted to each other. But, electrons move around and, for a split second, there is more negative charge on one side of one molecule, creating a temporary dipole. This induces a dipole in the very next molecule. These forces can also occur in polar molecules. NON POLAR COVALENT MOLECULES

21. POLAR COVALENT • Molecules w/ shared e- where atoms around the center are NOT the same • You have lone pairs around central atom. • Attracted by Dipole force: One end of the molecule is slightly negative, and the other end is slightly positive. Water molecule behaves as if it had a positive and negative end.

22. Properties of polar covalent compounds: • Dissolves in alcohol & water • Medium-low MP & BP • Non-conductor • S, l or g depends on mass

23. Dipole-Dipole Forces (permanent dipole): Dipole – a molecule in which one end has a partial positive charge and the other end has a partial negative charge POLAR COVALENT MOLECULES

24. Polar water molecules Strongly attracted to (+) ions by their (-) ends. Strongly attracted to (-) ions by their (+) ends.

25. DOT DIAGRAMS FOR MOLECULAR COMPOUNDS • Choose a central atom (the most needy. NEVER HYDROGEN OR A HALOGEN) • Arrange other atoms around central atom • Determine the number of valence electrons for each atom based on the periodic table (draw the correct number of “dots” around each atom) • Pair electrons so that each atom follows the octet rule (or duet rule for Hydrogen, 6 for Boron) • Use double and triple bonds if necessary. HINTS: H, halogens never in center, always bond 1x O unless an ion, bonds 2x N usually bonds 3x C always in the center, always bonds 4x

26. COORDINATE COVALENT EXAMPLES: • Central atom gives both pair of electron for the bond. • As above, place the most “needy” atom in the middle. • Move electrons if necessary. Do not allow the central atom to have more than 8 electrons. Instead, “give” the electrons to another atom or atoms that need them!

27. VSEPR • How many things are around central atom? • What structure is this molecule based on? • Which atoms are replaced by lone pairs? • What is the final structure, and what are the bond angles? TRIGONAL PLANAR LINEAR TETRAHEDRAL PYRAMIDAL BENT

28. Determining Molecular Shapes Valence Shell Electron Pair Repulsion (VSEPR) is bases on: • Shared and unshared pairs of electrons repel each other • An unshared pair of electrons repels more strongly than a shared pair • For the purpose of this model, a double or triple bond is considered equivalent to a single bond • The shape of a molecule or ion is the result of the shared and unshared pair of electrons being placed as far from each other as possible To apply VSEPR, we look at the central atom and count the # of shared and unshared pair of electron associated with it.

29. LINEAR • All diatomic molecule (X2, XY) • Formula XY2No lone pairs on central atom! Best arrangement that allows the electron pairs to be as far apart as possible

30. TRIGONAL PLANAR • Formula XY3No lone pairs on central atom!

31. TETRAHEDRAL • Formula XY4No lone pair on central atom!

32. PYRAMIDAL (Trigonal Pyramidal) • Formula XY3E ONElone pair! • (E=electron pair)

33. BENT or ANGULAR • Formula XY2E2ONE or TWOlone pairs! • (E=electron pair) One lone pair

35. Multiple Bonds • Atoms will form single or multiple bond depending on what is needed to make an octet Single bond • Sharing a pair of electron Double bond • Sharing two pairs of electrons Triple bond • Sharing 3 pairs of electrons O2 total of 12 electrons Nitrogen gas: N2 Total # of valence electron = 10