1. Different Types of Bonds Electronegativity Ionic / Polar Covalent / Nonpolar Covalent Metallic Bonding

2. Electronegativity • Electronegativity is defined as the ability of an atom to attract electron density to itself when joined to another atom in a chemical bond. • The most electronegative elements have the greatest “attraction” for electrons • Periodic Trends for Electronegativity?

3. Electronegativity Values

4. Electronegativity • Electronegativity is defined as the ability of an atom to attract electron density to itself when joined to another atom in a chemical bond. • The most electronegative elements have the greatest “attraction” for electrons • Periodic Trends for Electronegativity? • Pauling assigns values to each atom • Scale from 0-4

5. Electronegativity Differences • The difference between electronegativity values of two atoms determines what kind of bond it is • >1.7 Ionic • Electrons completely transferred • 0.0 – 0.4 Nonpolar Covalent • Electrons shared equally • 0.4 – 1.7 Polar Covalent • Electrons shared unequally

6. Electronegativity Differences

7. Polar Covalent Bonds • Unequal sharing of electrons results in one side of the molecule being “negative” and the other side being “positive” • HCl • There is a greater e- density around one atom than there is around the other • Which one?

8. Polar Covalent BondsHCl The e- cloud around chlorine is bigger than the e- cloud around hydrogen This molecule will behave differently than Cl-Cl because of the uneven distribution of electrons

9. Representing Polar Covalent Bonds • Two methods • “Plus Arrow” • Plus sign over less elecneg… atom • What does the arrow represent?

10. Representing Polar Covalent Bonds • Two methods • “Lowercase” Delta () • Represents “kinda” or “sorta” • One side of the bond is “kinda” negative

11. Polar Bonds vs. Polar Molecules • Just because a molecule has polar bonds does not mean that it is a polar molecule • CCl4 • Every bond in this molecule is polar, but because they are all polar in opposite directions, they cancel the effect of each other • This molecule will behave “nonpolar”

12. Metallic Bonding • Bonding found in metallic solids (crystals) • A metallic solid can be pictured as a 3D network of positive nuclei that remain fixed in a crystal lattice • Loosely-held valence electrons move freely throughout the crystal

13. Metallic Bonding

14. Metallic Bonding • Bonding found in metallic solids (crystals) • A metallic solid can be pictured as a 3D network of positive nuclei that remain fixed in a crystal lattice • Loosely-held valence electrons move freely throughout the crystal • The fluid-like movements of the valence electrons make metals good conductors of heat and electricity.