Transcript Slide 1

Periodic Properties
properties electron configurations nuclear charge
hydrogen atom 1 electron
1s1
Z=1
E =- RH
Z2
1
nf 2
-
1
ni2
to remove e- nf = ∞
from ground state ni = 1
E =2.178 x 10-18 J x 6.022 x 1023 atoms = 1311 kJ
atom
mol
mol
Ionization Energy, I
H
1s1 Z = +1 E = 1311 kJ/mol
He+
1s1 Z = +2 E = 5250 kJ/mol
-
-
+
E =- RH
2+
Z2
1
nf 2
-
1
ni2
= 5250 kJ/mol
higher nuclear charge lowers orbital energy
stabilizes system
systems with more than 1 electron
studied experimentally ionization reactions
1. Effect of 2 electrons in same orbital
He+ 1s1
E = 5250 kJ/mol
He 1s2 E = 2372 kJ/mol
Z = +2 same nuclear charge
-
2+
-
2+
-
orbital energy higher
e- e- repulsion
less stable
easier to remove e-
2. Effect of electrons in different orbital
E = 520 kJ/mol
E = 2954 kJ/mol
Li ground state 1s2 2s1
Li2+ excited state 2s1
Z = +3 same nuclear charge
2s
2s
1s
1s
-
3+
-
-
-
3+
inner electrons shielding charge
Zeff < Z
3. Effect of orbital shape
E = 520 kJ/mol
E = 341 kJ/mol
Li ground state 1s2 2s1
Li excited state 1s2 2p1
Z = +3 same nuclear charge
2s
2p
1s
-
-
3+
-
1s
-
3+
-
-
s orbitals penetrating lower energy
Potential Energy determines orbital energies
1. Greater nuclear charge (Z) lowers energy
electrons more difficult to remove
2.
Electron-electron repulsion raise energy
electrons easier to remove
electrons shield Z
inner electrons shield better
3. Orbitals with more penetration lower energy
electrons more difficult to remove
s<p<d<f
I1 increase Z increases shielding stays same
adding valence ecore e- unchanged
I1 decrease Zeff decreases more shielding ecore e-
2p
2p
-
-
2s
2s
1s
1s
-
-
-
-
-
5+
10+
-
-
-
-
-
B
-
Ne
2p
-
2s
2s
1s
1s
-
-
-
-
4+
5+
-
-
-
B
Be
N
O
e- e- repulsion
Second Ionization Energy
I1
Na
I2
I3
I4
I5
I6
I7
495 4560
Mg 735
Al 580
Si 780
P 1060
S 1005
1445 7730
1815
11,600
1575
16,100
1890
21,200
2260
27,000
very
difficult
to
remove
Cl 1255 2295
core electrons
Ar 1527 2665
Atomic Radius
increase in size n dominates
decrease in size
Zeff dominates
Electron Affinity
Energy given off when a gas phase atom gains e-
Cl (g) + e-  Cl- (g)
Increases
Zeff increases
Noble gases – no tendency to gain e-
Summary
atomic radius decreases
ionization energy increases
electron affinity increases
Zeff
atomic radius increases
n
ionization energy decreases
metals lose
e-
non-metals gain e-