ch 8 periodic relationships
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Periodic Relationships Amongthe Elements
Chapter 8
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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When the Elements Were Discovered
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n s 1
n s 2
n s 2 n p 1
n s 2 n p 2
n s 2 n p 3
n s 2 n p 4
n s 2 n p 5
n s 2 n p 6
d 1
d 5
d 1 0
4f
5f
Ground State Electron Configurations of the Elements
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Classification of the Elements
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Electron Configurations of Cations and Anions
Na [Ne]3s1 Na+ [Ne]
Ca [Ar]4s2 Ca2+ [Ar]
Al [Ne]3s23p1 Al3+ [Ne]
Atoms lose electrons so thatcation has a noble-gas outerelectron configuration.
H 1s1 H- 1s2 or [He]
F 1s22s22p5 F- 1s22s22p6 or [Ne]
O 1s22s22p4 O2- 1s22s22p6 or [Ne]
N 1s22s22p3 N3- 1s22s22p6 or [Ne]
Atoms gain electronsso that anion has anoble-gas outerelectron configuration.
Of Representative Elements
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+ 1
+ 2
+ 3
- 1
- 2
- 3
Cations and Anions Of Representative Elements
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Na+: [Ne] Al3+: [Ne] F-: 1s22s22p6 or [Ne]
O2-: 1s22s22p6 or [Ne] N3-: 1s22s22p6 or [Ne]
Na+, Al3+, F-, O2-, and N3- are all isoelectronic with Ne
What neutral atom is isoelectronic with H- ?
H-: 1s2 same electron configuration as He
Isoelectronic: have the same number of electrons, andhence the same ground-state electron configuration
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Electron Configurations of Cations of Transition Metals
When a cation is formed from an atom of a transition metal,electrons are always removed first from the ns orbital and
then from the (n – 1)d orbitals.
Fe: [Ar]4s23d6
Fe2+: [Ar]4s03d6 or [Ar]3d6
Fe3+: [Ar]4s03d5 or [Ar]3d5
Mn: [Ar]4s23d5
Mn2+: [Ar]4s03d5 or [Ar]3d5
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Effective nuclear charge (Z eff) is the “positive charge” feltby an electron.
Na
Mg
Al
Si
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12
13
14
10
10
10
10
1
2
3
4
186
160
143
132
Z effCoreZ Radius (pm)
Z eff = Z - σ 0 < σ < Z (σ = shielding constant)
Z eff ≈ Z – number of inner or core electrons
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Effective Nuclear Charge (Z eff)
increasing Z eff
i n c r e a s i n g
Z e f f
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Atomic Radii
metallic radius covalent radius
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Trends in Atomic Radii
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Comparison of Atomic Radii with Ionic Radii
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Cation is always smaller than atom fromwhich it is formed.Anion is always larger than atom fromwhich it is formed.
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The Radii (in pm) of Ions of Familiar Elements
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Chemistry in Action: The 3rd Liquid Element?
L i q ui d ?
117 elements, 2 are liquids at 250C –Br2 and Hg
223Fr, t1/2 = 21 minutes
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Ionization energy is the minimum energy (kJ/mol) requiredto remove an electron from a gaseous atom in its groundstate.
I 1 + X (g) X+(g) + e-
I 2 + X+(g) X2+
(g) + e-
I 3 + X2+(g) X3+
(g) + e-
I 1 first ionization energy
I 2 second ionization energy
I 3 third ionization energy
I 1 < I 2 < I 3
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Filled n=1 shell
Filled n=2 shell
Filled n=3 shell
Filled n=4 shellFilled n=5 shell
Variation of the First Ionization Energy with Atomic Number
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General Trends in First Ionization Energies
Increasing First Ionization Energy
I n c r e a s i n g
F i r s t I o n i z a t i o n
E n e r g y
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Electron affinity is the negative of the energy change thatoccurs when an electron is accepted by an atom in thegaseous state to form an anion.
X (g) + e - X-(g)
F (g) + e - X-(g)
O (g) + e - O-(g)
∆H = -328 kJ/mol EA = +328 kJ/mol
∆H = -141 kJ/mol EA = +141 kJ/mol
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Variation of Electron Affinity With Atomic Number (H – Ba)