Transcript Chapter 6: Periodic Trends

Are all atoms the same size?
Na
Mg
Al
Si
P
S
Cl
So then...
Na
Mg
Al
Si
P
S
Cl
Actually...
Na
Mg
Al
Si
P
S
Cl
It has to do with Zeff
Na
Mg
Al
Si
P
S
Cl
Ya! Zeff
• Zeff = Z − S
• where
–Z is the number of protons in the
nucleus (atomic number)
–S is the average number of
electrons between the nucleus and
the electron in question (the
number of nonvalence electrons).
Lets review...
Proton
+
e-
What happens if you get...
Proton
+
Proton
+
e-
What happens to the # of protons
as you go across Periodic Table?
11 12
13
14
15
16
17
Think of protons as...
Atom
So as you go across the
periodic table, the nuclear
charge gets stronger!
What about down a group???
• Remember electrons repel
I Hate You
Your so
negative!
So more e- shells...
11
You guys
are pushy!
19
Who will get the messiest???
So more shells...
Weaken the effect of the nucleus
More Protons...
Strengthen the effect of the
nucleus
Periodic Law
• Elements are arranged in order of increasing
atomic #, their physical and chemical
properties show a periodic (repeating) pattern.
Periodic Trends: Atomic Radii
A. Definitions
1. Nuclear Charge: number of protons
2. Shielding effect: inner electrons block
outer electrons from attraction to nucleus
B. Trends
• How to predict trends:
–1. Distance from nucleus
–2. Nuclear charge (Strength of nucleus)
C. Atomic Radii (size)
1. Atom size increases going down a group
•
Why?: more energy levels (more shielding)
C. Atomic Radii
2. Atom size decreases going across a
period left to right
• Why?: same amount of shells, but more
protons= stronger pull
Atomic Radii Trend
1. Size of atom
2. Period: (Left to Right) Decreases
•
Why? Same # shells, stronger nucleus
3. Group: (Top to Bottom) Increases
•
Why? More shells, more shielding
Examples
• Which atom has the larger radius?
Be
or Ba
Ba
Ca
or Br
Ca
Periodic Trends Practice
1. ATOMIC RADIUS
Rank them from smallest to largest
a. Li, C, F
F, C, Li
b. Li, Na, K Li, Na, K
c. Ge, P, O O, P, Ge
N, C, Al
d. C, N, Al
e. Al, Cl, Ga Cl, Al, Ga
C. Ionic Radius (ion size)
1. Cations (+) :lose e-  gets smaller
2. Anions (–): gain e-  gets bigger
© 2002 Prentice-Hall, Inc.
Examples
• Which particle has the larger radius?
S or
Al
2S
or
2S
3+
Al
Al
Periodic Trends Practice
• 2. Ionic Radius: Which species will have
the smaller atomic radius?
K+
a) K+ or K
________
2+
2+
Ba
b) Ba or Ba ________
Cl
c) Cl- or Cl
________
Se
d) Se2- or Se ________
P2e) P3- or P2- ________
XII. Periodic Trends: Ionization
energy and Electronegativity
A. Ionization energy Trend
1. Energy required to remove an electron
2. Period: (Left to Right) Increases
•
Why? Nucleus gets stronger (Hard to steal)
3. Group: (Top to Bottom) Decreases
•
Why? More shells, weaker nucleus (easy to steal)
Examples
• Which atom has the higher 1st Ionization
Energy?
N or Bi
N
Ba
Ne
or Ne
Periodic Trends Practice 2
1. IONIZATION ENERGY
Rank them from lowest to highest
Mg, Si, S
a. Mg, Si, S
b. Mg, Ca, Ba Ba, Ca, Mg
Br, Cl, F
c. F, Cl, Br
d. Ba, Cu, Ne Ba, Cu, Ne
e. Si, P, He Si, P, He
B. Electronegativity Trend
1. Ability to attract outside electrons in a bond
2. Period: (Left to Right) Increases
•
Why? Nucleus gets stronger (Pulls in e- better)
3. Group: (Top to Bottom) Decreases
•
Why? More shells, weaker nucleus (other efurther away, harder to pull in)
Periodic Trends Practice 2
2. ELECTRONEGATIVITY
Rank them from lowest to highest
a. Li, N, C
Li, C, N
b. C, Ne, O C, O, Ne
c. O, Si, P
Si, P, O
d. P, K, Mg K, Mg, P
e. S, He, F S, F, He
Nuclear charge increases
Shielding increases
Atomic radius increases
Ionic size increases
Ionization energy decreases
Electronegativity decreases
Summary
Shielding is constant
Atomic Radius decreases
Ionization energy increases
Electronegativity increases
Nuclear charge increases