1. Bonding: General Concepts
Chapter 8

2. Words to know: chemical bond ionic bond covalent bond metallic bond
Lewis Symbol
Octet rule

3. Practice
Classify the following compounds as ionic or covalent. Justify your answer. Which compounds contain both types of bonds? - KBr - SO2 - H2SO4 - CH3COOH - Na3PO4 - CaCO3

4. Lewis Symbol
Element symbol with valence electrons written around it as dots
Elements want to gain, lose, or share electrons to look like a noble gas (isoelectronic)

5. Place the following chemical species into isoelectronic groups:
N3-, K+, Ca2+, O2-, F-, Ne, Br, Kr, Sc3+, Na+, Al3+, Se2-, Mg2+

6. Ionic Bonding
electrons are transferred from an atom with low electronegativity to one with high EN
electrostatic attraction between the two oppositely charged ions
arranged in a crystal lattice (lattice energy, DHL, is energy required to completely separate solid ionic compound into gaseous ions)

7. Lattice Energies?
Lattice energy increases when the atoms are smaller or have a higher charge (exchanging more electrons)
higher lattice energy means the ionic compound is more strongly bonded
high lattice energies also explains why ionic compounds are brittle and hard

8. In each of the following pairs of compounds, identify the one with the higher lattice energy
KCl, CaS
LiF, NaCl
Fe2O3, MnO2
CaO, CaCl2

9. Ions
Representative elements follow the “hill of oxidation numbers” when in ionic compounds
transition metals (including lead & tin) are a little weird:
Their valence electrons are the highest filled s sublevel and occasionally 1 or more of their d electrons

10. Transition Metal Ions Iron Lead Fe: [Ar] 4s23d6 Fe2+: [Ar] 3d6
Pb: [Xe] 6s24f145d106p2
Pb2+: [Xe] 6s24f145d10
Pb4+: [Xe] 4f145d10

11. Write the electron configurations for Cr3+ and Sn4+

12. Covalent Bonding 2+ atoms sharing electrons
Lewis structures show shared and lone pairs of electrons
polar or non-polar determined by difference in EN values for the 2 bonding elements
0-0.4 = NPC
= PC
= really PC
>2.0 = ionic

13. Dipoles
With polar covalent bonds, there is a dipole (one end of the bond hogs the “shared” electrons a little more than the other)
symbolized with d+ and d- and are not whole number charges

14. Drawing Lewis Structures
Add up the total valence electrons of all bonding atoms
Use one pair of electrons to bond each outer atom to the central atom (usually the least EN or the one present in the least abundance)
Complete octets around all of the outer atoms
Place any remaining electrons around the central atom
If there aren’t enough electrons to give the central atom an octet, make multiple bonds

15. Practice
Write the Lewis structures for each of the following compounds:
NO3-
CO2
PCl5
NO3

16. Resonance Structures
used when 2+ Lewis structures are equally good representations of the bonds
actual structure is kind of an average of all the possibilities
examples include ozone & nitrate ion

17. Exceptions to Octet Rule
When there is an odd # of electrons, one atom will only have 7 electrons around it. (NO, NO2)
When the compound has a group 2 or 3 element as the central atom, the number of electrons around the central atom will be twice the group number
If central element is big, it can have an expanded octet (PCl5)

18. Covalent Bond Strength
Multiple covalent bonds are stronger than single covalent bonds (they are also shorter)
Higher the number of electrons shared, the stronger the bond