are all atoms the same size? namgalsipscl. so then... namgalsipscl
TRANSCRIPT
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 1314
1516
17
Think of protons as...
AtomProton
+
Proton
+
So as you go across the periodic table, the nuclear
charge gets stronger!
What about down a group???
• Remember electrons repelYour so
negative!I Hate You
So more e- shells...
1119
You guys are pushy!
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)
1. Atom size increases going down a group
• Why?: more energy levels (more shielding)
C. Atomic Radii (size)
2. Atom size decreases going across a period left to right
• Why?: same amount of shells, but more protons= stronger pull
C. Atomic Radii
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
• Which atom has the larger radius?
Be or Ba
Ca or Br
Ba
Examples
Ca
Periodic Trends Practice
1. ATOMIC RADIUS
Rank them from smallest to largest
a. Li, C, F
b. Li, Na, K
c. Ge, P, O
d. C, N, Al
e. Al, Cl, Ga
F, C, Li Li, Na, K
O, P, Ge N, C, Al
Cl, Al, Ga
1. Cations (+) :lose e- gets smaller
© 2002 Prentice-Hall, Inc.
2. Anions (–): gain e- gets bigger
C. Ionic Radius (ion size)
• Which particle has the larger radius?
S or S2-
Al or Al3+
S2-
Examples
Al
Periodic Trends Practice
• 2. Ionic Radius: Which species will have the smaller atomic radius?a) K+ or K ________
b) Ba2+ or Ba ________
c) Cl- or Cl ________
d) Se2- or Se ________
e) P3- or P2- ________
K+ Ba2+ Cl Se 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)
• Which atom has the higher 1st Ionization Energy?
N or Bi
Ba or Ne
N
Examples
Ne
Periodic Trends Practice 2
1. IONIZATION ENERGY
Rank them from lowest to highest
a. Mg, Si, S
b. Mg, Ca, Ba
c. F, Cl, Br
d. Ba, Cu, Ne
e. Si, P, He
Mg, Si, S
Ba, Ca, Mg
Br, Cl, F
Ba, Cu, Ne
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 e-
further away, harder to pull in)
Periodic Trends Practice 2
2. ELECTRONEGATIVITY
Rank them from lowest to highest
a. Li, N, C
b. C, Ne, O
c. O, Si, P
d. P, K, Mg
e. S, He, F
Li, C, N
C, O, NeSi, P, O
K, Mg, P S, F, He
Summary
Shielding is constantAtomic Radius decreasesIonization energy increasesElectronegativity increasesNuclear charge increases
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