Transcript
8/14/2019 Lecture 5.1 - Periodic Properties 1
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Periodic Properties of theElements
Part I
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Mendeleev’s Original Periodic Table
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Isoelectronic (Series)
Species having the same ground-stateelectron configuration are isoelectronic
Ex:
Mg2+, F-, Na+, Ne, Al3+, O2-, N3-
All the above species are part of the sameisoelectronic series
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Periodicity:
Properties of elements repeat and vary
depending on their location in the periodictable
• Effective Nuclear Charge• Atomic Radius
• Ionic Radius
• Ionization Energy (I 1, I
2 , …)
• Electron Affinity
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Effective Nuclear Charge
Zeff : the positive charge (from nucleus) feltby an electron
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☼ Zeff
is the result of opposing forces
☼ As Zeff
increases, e- will experience greater
attraction to the nucleus
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☼ Use Zeff
estimates to compare elements
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Ex:
Ne 1s2
2s2
2p6
shield e-
outermost e-
10 p+
4 e-
Zeff = Z – S = – = +6
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Ex:
F 1s2
2s2
2p5
shield e-
outermost e-
9 p+
4 e-
Zeff = Z – S = – = +5
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Effective nuclear charge
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Zeff Ne > Zeff F
• Equal e- shielding
• Ne has more protons than F
• Ne outermost e- experience greater attractive force
towards the nucleus
☼ the strength of attraction between theoutermost e- and the nucleus determinesan atom’s periodic properties
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Atomic Radius
•One-half the distance between two adjacent nuclei
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Atomic radius decreases across the periodictable to the right.
Atomic radius increases as you go down the
table.
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☼ As Zeff decreases, atomic radius
increases (e- are held with less force
thus farther from the nucleus)
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Ex: Atomic radius of K > Ca. Why?
K 1s2 2s2 2p6 3s2 3p6 4s1
18 e-
Zeff = – = +1
19 p+
Ca 1s2 2s2 2p6 3s2 3p6 4s2
Zeff = 20 – 18 = +2
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K > Ca
• Equal e-
shielding• Ca has one more proton than K
• Zeff Ca > Zeff K
• Ca outermost e- experience more attractive force towards
the nucleus
☼ Ca outermost e- are pulled closer to thenucleus than those of K
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Ionic Radii- Cations•
radius decreases due to an increase in Zeff
•Cations are smaller than their parent atom
Ca 1s2 2s2 2p6 3s2 3p6 4s2
Zeff = – =20 18 +212 +8
2+
Zeff Ca < Zeff Ca2+
Ca2+ is smaller than Ca
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Ionic Radii- Anions
• radius increases due to crowding of more e-
into a subshell
• additional repulsion between e- forces them
farther from nucleus
• Anions are larger than their parent atom
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Ex: Rank the following isoelectronic series in
order of decreasing size:
Rb1+, Sr 2+, Se2-, Br 1-
Se2- > Br 1- > Rb1+ > Sr 2+
Rb1+ Zeff = 37 - 30 = +7
Sr 2+ Zeff = 38 - 30 = +8
Se2- Zeff = 34 - 30 = +4
Br 1-
Zeff = 35 - 30 = +5
Ionization Energy
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Ionization Energy
• Minimum energy required to remove
the outermost electron form an isolatedneutral atom in the gaseous state.
• kJ/mol
• X(g) X+(g) + e
-
• ∆H = I1 (1st Ionization Energy)
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Why?
☼ As Zeff
increases, e- are held with more
force
☼ As attractive force increases, more
energy is required to remove an e-
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break
HW: p. 339 # 82, 85, 86p. 340 # 87, 88, 90
LP: Lab 9 (both parts)
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