1. Bonding Revisited Few things are truly black-or-white

2. Previous Pictures Ionic: charges, no shared electrons. Covalent: completely shared electrons But just like siblings, not all elements share well…

3. New Picture Bonding is more like a spectrum, which ranges from perfectly shared, to completely unshared. Many compounds have covalent bonds that are unevenly shared.

4. New Picture If the electrons aren’t shared evenly, then the atoms aren’t exactly neutral. But if they’re not all the way over, they’re not exactly +1 and -1 either. Atom A is partially positive (δ+) and atom B is partially negative (δ-)

5. Electronegativity Electronegativity: how strongly an atom pulls on shared electrons. There are values you can look up, but we’ll mostly just use categories:

6. Electronegativity Electronegativity: how strongly an atom pulls on shared electrons. There are values you can look up, but we’ll mostly just use categories: The King: Fluorine.

7. Electronegativity Electronegativity: how strongly an atom pulls on shared electrons. There are values you can look up, but we’ll mostly just use categories: The King: Fluorine. Very strong: Oxygen, Nitrogen, Chlorine

8. Electronegativity Electronegativity: how strongly an atom pulls on shared electrons. There are values you can look up, but we’ll mostly just use categories: The King: Fluorine. Very strong: Oxygen, Nitrogen, Chlorine Pretty strong: Phosphorous, Sulfur, Bromine, Iodine

9. Electronegativity Electronegativity: how strongly an atom pulls on shared electrons. There are values you can look up, but we’ll mostly just use categories: The King: Fluorine. Very strong: Oxygen, Nitrogen, Chlorine Pretty strong: Phosphorous, Sulfur, Bromine, Iodine Wimpy: Carbon, Hydrogen, Silicon

10. Electronegativity Electronegativity: how strongly an atom pulls on shared electrons. There are values you can look up, but we’ll mostly just use categories: The King: Fluorine. Very strong: Oxygen, Nitrogen, Chlorine Pretty strong: Phosphorous, Sulfur, Bromine, Iodine Wimpy: Carbon, Hydrogen, Silicon Super weak: metals

11. Tug-of-War Whether a bond is non-polar, polar, or covalent depends on the electronegativity of the atoms compared: Same strength: nobody wins—perfectly covalent (The only difference strength makes is how strong the bond is—two elements pulling hard makes it weaker than two pulling weakly)

12. Tug-of-War Whether a bond is non-polar, polar, or covalent depends on the electronegativity of the atoms compared: Similar strengths: uneven distribution—polar covalent The more electronegative element will have a partial negative, and the less partially positive.

13. Tug-of-War Whether a bond is non-polar, polar, or covalent depends on the electronegativity of the atoms compared: Very different strengths: Completely stole the rope—ionic The more electronegative element just takes the electrons—becomes negative. This basically only happens with metal compounds (hence our rule about metal compounds being ionic)

14. Drawing the Polarity The polarity is either shown with the partial charge symbols (δ+ and δ-) or with arrows: C—O Cl—H Arrow’s plus-sign-looking end goes with the partially positive atom, and point with the partially negative end. Sometimes the lengths of the arrow are used to show when one is more or less polar.

15. How Bonds are Made To make a bond, electrons have to overlap. There are two ways for this to happen: 1. Directly overlapping: sigma (σ) bond The first bond made between any two atoms is always a sigma bond

16. How Bonds are Made To make a bond, electrons have to overlap. There are two ways for this to happen: 2. Once the space in between is used up, you have to find another way: pi (π) bonds Made with parallel p orbitals These are the second and third bonds of double/triple bonds.

17. How Bonds are Made H—C  N Sigma bond Sigma bond and two pi bonds

18. Summary Many bonds aren’t perfectly shared. These are polar (have partial charges) Electronegativity is how much atoms pull on shared electrons Polar bonds come from uneven electronegativity Bonds can be made two ways: Direct overlap (sigma) Aligned p orbitals (pi)