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1.1 Effective Nuclear Charge
The interaction between the nuclear charge and thevalence electrons (how many? how far away?) iscritical
The nuclear charge experienced by the valenceelectrons (Z
eff
) impacts how tightly the valence
electrons are held
How tightly the valence electrons are held influences
How tightly the valence electrons are held influencesatomic size, ionization energy, electron affinity, andreactivity
Periodic Trends
1.2 Effective Nuclear Charge
Z
eff
= nuclear charge actually experienced by an electron
Simplest approximation
Z
eff
= Z - # core electrons
Assumption
Examples
1.3 Effective Nuclear Charge
Slater’s rules acknowledge the imperfect shieldingcaused by orbital penetration
Periodic Trends
1.4 Slater’s Rules
Slater’s rules assume imperfect shielding
Z
eff
= Z –
where
is calculated using Slater’s rules
1
G
th
bit l
i^
d
- Group the orbitals in order:
(1s) (2s,2p) (3s,3p) (3d) (4s,4p) (4d) (4f) (5s,5p)…
- To determine
, sum up the following contributions for the
electron of interest: a. 0 (zero) for all electrons in groups outside (to the right of) the
one being considered b. 0.35 for each of the other electrons in the same group (except
g^
p (
p
for 1s group where 0.30 is used) c. If the electron is in a (ns,np) group, 0.85 for each electron in the
next innermost (to the left) group d. If the electron is in a (nd) or (nf) group, 1.00 for each electron in
the next innermost (to the left) group e. 1.00 for each electron in the still lower (farther in) groups
1.5 Using Slater’s Rules
What do the 1.0, 0.85 and 0.35 factors mean?
Some examples
Na
F
Periodic Trends
1.6 Using Slater’s Rules
Fluorine’s Z
eff
calculated using the simple
approximation = 7 and using Slater’s rules = 5.20.Why is the Slater Z
eff
value lower? eff
What is Z
eff
for a “core” electron?
1.7 Using Slater’s Rules
Z
eff
trend across a period (Li to Ne)
Periodic Trends
1.8 Using Slater’s Rules
Z
eff
trend down a group (Li to K)
Z
eff
trend down a group (F to Br)
2.5 Electron Affinity
1
2
13
14
15
16
17
Periodic Trends
2.6 Electron Affinity
2.7 Electron Affinity
Some exceptions to the general trend
Li and Be
C and N
Periodic Trends
2.8 Electron Affinity
Another exception to the general trend
F and Cl (O and S)
2.9 Electronegativity
Periodic Trends
2.10 Ionic Radii
Cs
+^
> K
+^
Na
- I
Br
Cl
Na versus Na
Wh t
b^
t^
lfid
hl
id
d^
t^
i^
i^
What about sulfide, chloride and potassium ions?
3.1 Chemical Bonding
Covalent
Ionic
Metallic
Periodic Trends
3.2 Chemical Bonding
Covalent
Ionic
Metallic
Metallic
2.5 Electron Affinity
1
2
13
14
15
16
17
Periodic Trends
4.2 Uniqueness Principle
Small size
4.3 Uniqueness Principle
Tendency to form
-bonds
Periodic Trends
4.4 Uniqueness Principle
Absence of d orbitals of appropriate energy
5.1 Diagonal Effect
Diagonal relationship (similar chemical properties)between first member of a group and the secondmember of the next groupmember of the next group
Li and Mg
Be and Al
B and Si
Periodic Trends
5.2 Diagonal Effect
Why does this diagonal relationship exist?
6.1 Metals, Non-metals, Metalloids
Periodic Trends
6.2 Oxidation State and Reactivity
