Chem 104A, UC, Berkeley Periodic Trendsnanowires.berkeley.edu/teaching/104a/201404.pdfPeriodic...
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1 Chem 104A, UC, Berkeley Periodic Trends Generally, atoms with same outer-orbital structure appear in the same Column. Chem 104A, UC, Berkeley Example: H2: d=0.74 Å rH=0.37 Å Estimating bond distance (covalent): R----C-H: d C-H = rC + rH =0.77 + 0.37 =1.14 Å Effective atomic radius (covalent radius) effective atomic radius =1/2(d AA in the molecule A 2 )
Transcript of Chem 104A, UC, Berkeley Periodic Trendsnanowires.berkeley.edu/teaching/104a/201404.pdfPeriodic...
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Chem 104A, UC, Berkeley
Periodic Trends
Generally, atoms with same outer-orbital structure appear in the same Column.
Chem 104A, UC, Berkeley
Example:
H2: d=0.74 Å rH=0.37 Å
Estimating bond distance (covalent):
R----C-H: d C-H = rC + rH =0.77 + 0.37 =1.14 Å
Effective atomic radius (covalent radius)
effective atomic radius =1/2(dAA in the molecule A2)
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Chem 104A, UC, Berkeley
Trend 1. Atomic radii increase down a group (Zeff ~constant while n increases).
Trend 2: Atomic radii decrease across a period (Zeff increase)
Chem 104A, UC, Berkeley
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Chem 104A, UC, Berkeley
Na
K
Rb
1622 3221 spss
2.2285.0811 effZ
Zeff=2.2
2.21085.0819
433221 262622
effZ
spspss 1
Chem 104A, UC, Berkeley
Na Mg Al Si P S Cl
[Ne]
Z
Zeff
13s 23s 1233 ps 2233 ps 3233 ps 4233 ps5233 ps
11 12 13 14 15 16 17
8.8 9.15 9.5 9.85 10.2 10.55 10.9
2.2 2.85 3.5 4.15 4.8 5.45 6.1
1Z
35.0
65.0 effZ
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Chem 104A, UC, Berkeley
Ionization energy:Energy required to remove an electron from a gaseous atom or ion.
Trend 1: IE1 decrease down a group( n, r increase while Zeff constant).
Trend 2: IE1 increases across a period (Zeff increase, r decrease)
Exception: B, O ionization energy lower than Be, N: empty or half filled orbitals contribute to the stability.Similarly: Al, S
egAgA
egAgA
)()(
)()(2
2
1
IEE
IEE
Chem 104A, UC, Berkeley
22 21: ssB
322 221: pssO
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Chem 104A, UC, Berkeley
Chem 104A, UC, Berkeley
Electron affinity= energy required to remove an electron from the gaseous negative ion (ionization energy of anion).
maximum for halogens usually positive, difficult to measure, but can be
negative. EA(F) lower than EA(Cl):
smaller diameter, strong e-e repulsion
egAgA )()(EAE
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Chem 104A, UC, Berkeley
kJ/mol
Chem 104A, UC, Berkeley
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Chem 104A, UC, Berkeley
Total energies of an ion in various charge states:E=q +q2 (q =ionic charge)
The slope of this curve near the origin gives us an idea of how readily the atom accepts and gives up electrons.
Total energy E
0 Charge q
+1
-1
Electronegativity (EN)
Chem 104A, UC, Berkeley
Electronegativity (EN)The power of an atom in a molecule to attract electrons to itself
Mulliken definition: EN =1/2(IE1+EA)
Pauling definition:
EN(A) –EN(B) small A-B bonding mostly covalentEN(A)-EN(B) large A-B bonding has ionic component
ENA ENB 0.208 DEAB DEA2 DE
B2
DE =bond dissociation energy in kcal/molEN(F)=3.98
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Chem 104A, UC, Berkeley
Chem 104A, UC, Berkeley
Example:
HF
DE (H2) =103 kcal/molDE(F2) =37 kcal/molDE(HF)=135 kcal/mol
molkcalDEDE FH /6222
EN(F)-EN(H) = 78.162135208.0
EN(H) =2.2
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Chem 104A, UC, Berkeley
Trend 1. EN decrease down a groupTrend 2: EN increase across a period
H2.20
Li0.98
Be1.57
B2.04
C2.55
N3.04
O3.44
F3.98
Na0.93
Mg1.31
Al1.61
Si1.90
P2.19
S2.58
Cl3.16
K0.82
Ca1.00
Sc1.36
Ti1.54
V1.63
Cr1.66
Mn1.55
Fe1.83
Co1.88
Ni1.91
Cu2.00
Zn1.65
Ga1.81
Ge2.01
As2.18
Se2.55
Br2.96
Rb0.82
Sr0.95
Y1.22
Zr1.33
Nb1.60
Mo2.16
Te1.90
Ru2.20
Rh2.28
Pd2.20
Ag1.93
Cd1.69
In1.78
Sn1.96
Sb2.05
Te2.10
I2.66
Cs0.79
Ba0.89
La1.10
Hf1.30
Ta1.50
W2.36
Re1.90
Os2.20
Ir2.20
Pt2.28
Au2.54
Hg2.00
Tl2.04
Pb2.33
Bi2.02
Po2.00
At2.20
