1. CHAPTER 8
AP CHEMISTRY

2. BONDS Bond energy Ionic bonds coulomb’s law
energy required to break a bond
forms ions because it will have lowest energy this way
Ionic bonds
very stable, high melting point
NaCl, 800oC
electrostatic attractions of closely packed opposite charged ions
metal and nonmetal usually form these bonds
coulomb’s law
energy of interactions
E = 2.31 x J.nm (Q1Q2) r
Q1 and Q2 numerical charge
distance between the Na+ and Cl- is 2.76 Å

3. CONTINUE
A bond will form when the energy in a compound is lower than as separate atoms
this will minimize the sum of positive (repulsive) energy and negative (attractive) energy terms and is called the BOND LENGTH

4. ELECTRONEGATIVITY
Ability of an atom to attract shared electrons to itself
page 334
polarity
dipole moment >
б б- б- б- Б+
show the direction of bond polarities and which have dipole moment HCl, Cl2 , SO3, CH4, H2S

5. PREDICTING IONIC COMPOUNDS
Ca + O <=> Ca2+ + O 2-
calcium is transferring 2 electron‘s to the oxygen
Ion size determines structure and stability of ionic solids, properties of ions in aqueous solution, and the biological effects of the ions
positive ions are smaller than parent atoms
negative ions are larger than parent atoms
Isoelectronic ions have the same electron configuration as the noble gas it is close to.
N3-, O2-, F-, Ne, Na+, Mg2+, Al3+
page 341

6. LATTICE ENERGY change in energy when gaseous ions form ionic solids
page 256
lattice energy = k(Q1Q2), k = proportionality
( r ) constant
page
covalent bonds with ionic characteristics
dipole moment gives a covalent bond a percent of ionic character
(measured dipole moment X-Y) X 100
(calculated dipole moment X+ Y-)
compounds with more than 50% ionic characteristics are considered ionic compounds
If the compound when melted can conduct an electrical current it is called a SALT

7. COVALENT BONDING forces which hold nonmetal atoms together
because this bond consists of sharing electrons it is very stable
Why should the sharing of two electrons between two nuclei result in stability?
when two hydrogen atoms approach each other the electron of one atom is attracted to the other nucleus, this lowers the electrostatic energy of the system
by overlapping orbitals, energy can be exchanged and overall energy is reduced

8. LEWIS STRUCTURES
eight electrons in the valence shell are more valence electrons are in the outer most energy level stable
use dot diagrams to show this
number of valence electrons = 1 to 8
In the lewis structure a covalent bond is a line.
single bond = 2 electrons shared
double bond = 4 electrons shared
triple bond = 6 electrons shared
8 electrons will never be shared, too much repulsion

9. WRITING LEWIS STUCTURES
count the number of valence electrons
NH C2H4
5+3(1) = (4) + 4(1) = 12
CH3OH
4 + 3(1) = 14
draw a skeleton structure by joining the atoms by single bonds
central atom written first in the formula
the following are usually terminal atoms
H, Br, F, I, Cl, O
make sure all bonds are accountable
determine the number of valence electrons that have not been accounted for

10. CONTINUE draw the Lewis structures for hydroxide ion OH-
hydroxyl amine NH2OH
chlorate ion ClO3-
Cl2CO
HCN

11. RESONANCE FORMS
in certain cases, the Lewis structure does not adequately describe the properties of the ion or molecule that it represents
NO2-
the concept of resonance is involved whenever a single Lewis structure does not explain all bonds
write the three resonance forms for the nitrate ion
Formal charge
the charge on an atom in a molecule or ion that is calculated by assuming that all lone pairs of electrons shared by an atom, belong to the atom
Cf = Ev - (Eu + 1/2Eb)
Cf = formal charge, Ev = # of valence electrons
Eu= # of unshared electrons, Eb= # of bonded electrons

12. CONTINUE
the most likely Lewis structure is one where the formal charge is close to zero
any negative formal charge is on the most electronegative atom (not the central atom)
determine the formal charge in nitrogen (I) oxide
N-O-N
N-N-O

13. EXCEPTIONS TO THE OCTET RULE
molecules that contain an odd number of valence electrons
NO(11 valence electrons)
NO2 (17 valence electrons)
species that contain an odd number of electrons are paramagnetic (attracted by a charge)
less than a full octet of electrons
BF3
BeF2
expanded octet surrounded by more than four pairs of valence electrons
XeF2, XeF6, XeF4, SF4, SF6
draw the Lewis structure for ICl4-

14. BOND ENERGY
enthalpy change, ΔH, to break a bond in a mole of gaseous substance
go over page 365
endothermic if ΔH > 0
exothermic if ΔH < 0
ΔH = (bond energies broken) -(bond energies formed)
Cl-Cl(g) + H-CH3 <=> H-Cl(g) + Cl-CH3(g)
ΔH = Σ( ) - Σ( )
-114 kJ
estimate ΔH
H-N-N-H (g) N-N (g) + 2 H-H (g)
H H

15. CONTINUE bond strength and length bond polarity
as the number of bonds increase the length decreases making then stronger
bond polarity
nonpolar bond atoms share electrons equally (small electronegative difference)
polar bond atoms share electrons unequally (large electronegative difference)
ionic bond atoms do not share electrons (very large electronegative difference)
review oxidation numbers
what is the oxidation state of the underlined element
P2O5, NaH, Cr2O72-,SnBr4, BaO2