Lecture outline: Chapter 7Periodic properties
1. Electrostatic effects2 Atomic size2. Atomic size3. Ionization energy4 El t ffi it4. Electron affinity5. Summarize some periodic properties
1S. Ensign, periodic properties
Some important termsp• Electron configuration: the order of filling of
orbitals; tells us which orbitals are filled or partially filled
• Core electrons: those in filled shellsCore electrons: those in filled shells“inner shell electrons”
• Valence electrons: those beyond the filled• Valence electrons: those beyond the filled shells“o ter shell electrons”“outer shell electrons”
• Effective nuclear chargeZeff = Z - S
2S. Ensign, periodic properties
Electron configurations of the elements,color coded by subshell typey yp
3S. Ensign, periodic properties
How far are the electrons from the nucleus for three 1s e-
2s & 2p e-
He: 1s2
y
Noble gases (He, Ne, Ar)?2s & 2p e
Ne: 1s2 2s22p6
Ar: 1s2 2s22p6 3s23p6.
ron
dens
ityad
ial e
lect
r
1s e-
2 & 2Ra 2s & 2p e-
3s & 3p e-
1s e-
Distance from nucleus ( ) 1 Å 4S. Ensign, periodic properties
Electrostatic interactions are responsible for the differences in orbital sizes for different atoms
•particles with like charges repel one another (electrostatic repulsion)
•particles with opposite charges are attracted to each other (electrostatic attraction)
•The strength of an electrostatic attraction is directly related to g ythe relative magnitudes of the charges on the particles
•The strength of an electrostatic attraction is inversely relatedto the distance between the interacting particles
5S. Ensign, periodic properties
The potential energy of two interacting charged particles
QQkE 21 d
dQQkE 21= Q1 Q2
d
dQQdQQE 21∝d
S. Ensign, periodic properties6
Electrostatic interactions are responsible for the differences in orbital si es for different atomsdifferences in orbital sizes for different atoms
Zeff = Z - Sn = 4
eff
Nuclear charge (atomic #)Effective nuclear charge
Z p+ 1
n = 2
n = 3 Nuclear charge (atomic #)# of shielding electrons
•A simplified model for electronicZ p n = 1 A simplified model for electronic structure: treat all electrons of a given n value as if they were identical (they’re really not, of course)
•Assume that electrons in the same shell do not shield each
th ff ti lother effectively
7S. Ensign, periodic propertiesd
QQE 21∝
Electrostatic interactions are responsible for the differences in orbital si es for different atomsdifferences in orbital sizes for different atoms
He: 1s2 Zeff = Z - S
n = 4
eff
Nuclear charge (atomic #)Effective nuclear charge
2
n = 3
n = 4 Nuclear charge (atomic #)# of shielding electrons
2 p+ n = 1
n = 2 •Treat all electrons of a given shell (n value) as identical
•Assume that electrons in the same shell do not shield each other effectively
8S. Ensign, periodic propertiesd
QQE 21∝
Electrostatic interactions are responsible for the differences in orbital si es for different atomsdifferences in orbital sizes for different atoms
Ne: 1s2 2s22p6 Zeff = Z - S
n = 4
p eff
Nuclear charge (atomic #)Effective nuclear charge
2
n = 3
n = 4 Nuclear charge (atomic #)# of shielding electrons
n = 1
n = 210 p+ •Treat all electrons of a given
shell (n value) as identical
•Assume that electrons in the same shell do not shield each other effectively
9S. Ensign, periodic propertiesd
QQE 21∝
Electrostatic interactions are responsible for the differences in orbital si es for different atomsdifferences in orbital sizes for different atoms
Ar: 1s2 2s22p6 3s23p6 Zeff = Z - S
n = 4
p p eff
Nuclear charge (atomic #)Effective nuclear charge
2
n = 3
n = 4 Nuclear charge (atomic #)# of shielding electrons
n = 1
n = 218 p+ •Treat all electrons of a given
shell (n value) as identical
•Assume that electrons in the same shell do not shield each other effectively
10S. Ensign, periodic propertiesd
QQE 21∝
How far are the electrons from the nucleus for three
1s e-: Zeff = +18
He: 1s2y
from the nucleus for three Noble gases (He, Ne, Ar)?2s & 2p e-
He: 1sNe: 1s2 2s22p6
Ar: 1s2 2s22p6 3s23p6.ron
dens
ity
p p
adia
l ele
ctr
1s e-: Zeff = +10
2 & 2Ra 2s & 2p e-
3s & 3p e-
1s e-: Zeff = +2
Distance from nucleus ( ) 11S. Ensign, periodic properties
The concepts of nuclear charge, inner l t hi ldi d l t t tielectron shielding and electrostatic
attraction/repulsion are important in predicting three important chemical properties of atoms:p p
• Atomic size• Ionization energy• Electron affinityy
12S. Ensign, periodic properties
Atomic size (radius)( )
n = 3
18 p+ n = 1
n = 2
n = 3
n 1
Ar: 1s2 2s22p6 3s23p613
S. Ensign, periodic properties
Atomic size (radius)( )
Ar: 1s2 2s22p6 3s23p6p p
n = 2
n = 3
18 p+ n = 1
n = 2is really:
14S. Ensign, periodic properties
Atomic size (radius)( )
18 p+ n = 1
n = 2
n = 3
r = 0.97 Å = 97 pmp
Golf ball nucleus
15S. Ensign, periodic properties
Atomic radius: the typical distance from the nucleus to a boundary of the surroundingnucleus to a boundary of the surrounding
electron cloud• What defines the boundary?What defines the boundary?• Van der Waals radius (unbonded touching)
C l t di ( l l t d f b d l th• Covalent radius (calculated from bond lengths measured for molecules)
• Calculated radii from theoretical models• Calculated radii from theoretical models
S. Ensign, periodic properties16
Atomic radii of elements 1-57
300
pm)
200
250
c ra
dius
(p
150
atom
ic
100
0
50
atomic number of element0 10 20 30 40 50 60
0
S. Ensign, periodic properties17
Calculated atomic radii of s and p block elements
IIncreasinng atomic Increasing atomic radius from R to L in a rowradius fr
Increasing atomic radius from R to L in a row
rom T to BB
in a per
18
S. Ensign, periodic properties
riod
Two opposing effects from Left Right and Top Bottom:
increase n increase orbital sizeincrease n, increase orbital sizeIncrease Zeff, decrease orbital size
Increassing atomic Increasing atomic radius from R to L in a rowradius from
Increasing atomic radius from R to L in a row
m T to B
in a
19S. Ensign, periodic properties
17
a period
Li vs. Be (L to R)
Li: 1s2 2s1 Be: 1s2 2s2Li: 1s2 2s1 Be: 1s2 2s2
n = 2
n = 3
n = 2
n = 3
n = 1
n = 2
n = 1
n = 23 p+ 4 p+
20S. Ensign, periodic propertiesd
QQE 21∝
Li vs. Na (Top to Bottom)
Li: 1s2 2s1 Na: 1s2 2s22p6 3s1Li: 1s2 2s1 Na: 1s2 2s22p6 3s1
n = 2
n = 3
n = 2
n = 3
n = 1
n = 2
n = 1
n = 23 p+ 11p+
21S. Ensign, periodic propertiesd
QQE 21∝
Chapter 7 materialChapter 7 material
1. Electrostatic effects2. Atomic size3. Ionization energy4 Electron affinity4. Electron affinity
22S. Ensign, periodic properties
Ionization energy: The minimum energy required to remove an gy gy qelectron from the ground state of the isolated gaseous atom
X X+X(g) X+(g) + e-
When reported with units of kJ/mol, it is the energy required to remove one mol of electrons from one mol ofrequired to remove one mol of electrons from one mol of gaseous atoms
23S. Ensign, periodic properties
Ionization of the hydrogen atom:
H(g) H+(g) + e-
n = ∞“Zero point” E = 0
6n = 7
n = 8
Increasing E ΔE (+) for removing ann = 4
n = 5n = 6
removing an electron from the atom’s ground state
n = 3
ground state orbitn = 2
24
n = 1 “Ground state” E = (-)24
S. Ensign, periodic properties
Ionization of the sodium atom:
Na(g) Na+(g) + e-Na: 1s2 2s22p6 3s1
n = ∞“Zero point” E = 0
6n = 7
n = 8
Increasing EΔE (+)n = 4
n = 5n = 6
( )
n = 3 “Ground state” E = (-)
n = 2
25
n = 125
S. Ensign, periodic properties
Successive ionizations for Silicon
I. # Elec. Config. before and after ionization
Ion formed
Zefffelt by departing
Energy req. (kJ) to remove
Si: 1s2 2s22p6 3s23p2
e- e-
I1 [Ne]3s23p2
[Ne]3s23p1
Si+ +4 786
I [N ]3 23 1 Si2+ 4 1 577n = 3
n = 4
I2 [Ne]3s23p1
[Ne]3s2
Si2+ +4 1,577
I3 [Ne]3s2
[Ne]3s1
Si3+ +4 3,228n = 1
n = 2
n = 3
14 p+[Ne]3s1
I4 [Ne]3s1
[He}2s22p6
Si4+ +4 4,354
n 1
I5 [He}2s22p6
[He]2s22p5
Si5+ +12 16,100
2626S. Ensign, periodic propertiesd
QQE 21∝
2500
Periodic trends for the first ionization energy: X(g) X+(g) + e-
2000
ener
gy
1500
2000
niza
tion
1000
1500
first
ion
500
1000
0
500
atomic number of element0 10 20 30 40 50 60
0
2727S. Ensign, periodic properties
What determines the energy required to remove an electron from an outer shell?remove an electron from an outer shell?
• Zeff felt by the valence electron• Distance of electron from the nucleus
(reflected by atomic radius values)
-Z p+-
-
-
2828S. Ensign, periodic propertiesd
QQE 21∝
What happens to Zeff and atomic radius when f l ft t i ht i i d?we move from left to right in a period?
•Increase Zeff, increase I1eff, 1
•Decrease size, increase I1
2929S. Ensign, periodic propertiesd
QQE 21∝
What happens to Zeff and atomic radius when d i ?we move down in a group?
•Zeff stays same for a given groupeff y g g p
•Increase size, decrease I1
S. Ensign, periodic properties30d
QQE 21∝
2500
Some “irregularities” in the trend for first ionization energy
2000
2500 He
Ne
ener
gy
1500
2000
NF
Ar
niza
tion
1000
1500
HBe C
O PCl
first
io
500
1000
BMg
Al
SiS
0
Li NaAl
atomic number of element0 5 10 15 20
S. Ensign, periodic properties31
Explanation of trend irregularities: Be to B and Mg to Al
Zeff = Z - S3s
3p
2p
3p
eff2s
2p
n = 3 2s
2p3s
n = 31s
n = 110p+
n = 210p+
n = 2
n = 1
Si li ti “ i h ll” d l I lit bit l l i
Ne: 1s2 2s22p6Ne: 1s2 2s22p6
S. Ensign, periodic properties32
Simplistic “onion shell” model treats s and p orbitals of a given “n” value as having equal energies
In reality s orbitals are lower in energy than p orbitals for a given “n” value
y2000
2500
Ne
He
Explanation of trend irregularities”: Be to Bfir
st io
niza
tion
ener
gy
1000
1500
BeMg
B
C
N
O
F
Si
PS
ClAr
H
atomic number of element0 5 10 15 20
f
0
500 AlLi Na
3s
3pn = 3
2s2p
2s
2p4 p+
n = 2
n = 1Be: 1s2 2s2
1s
Be
3333S. Ensign, periodic properties
Be
y2000
2500
Ne
He
Explanation of trend irregularities”: Be to Bfir
st io
niza
tion
ener
gy
1000
1500
BeMg
B
C
N
O
F
Si
PS
ClAr
H
atomic number of element0 5 10 15 20
f
0
500 AlLi Na
3s
3pn = 3
2s2p
2s
2p5 p+
n = 2
n = 1B: 1s2 2s22p1
1s
B
3434S. Ensign, periodic properties
BA filled s orbital provides some shielding of the nuclear charge felt by an electron in a p orbital of the same “n” value
y2000
2500
Ne
He
Explanation of trend irregularities”: Mg to Alfir
st io
niza
tion
ener
gy
1000
1500
BeMg
B
C
N
O
F
Si
PS
ClAr
H
atomic number of element0 5 10 15 20
f
0
500 AlLi Na
2p3s
3p
3s
3p 2s
n = 2
3s
n = 3
2s
2p 10p+ n = 1
Mg: 1s2 2s22p63s2
1s
Mg
Mg: 1s 2s 2p 3s
3535S. Ensign, periodic properties
MgA filled s orbital provides some shielding of the nuclear charge felt by an electron in a p orbital of the same “n” value
y2000
2500
Ne
He
Explanation of trend irregularities”: Mg to Alfir
st io
niza
tion
ener
gy
1000
1500
BeMg
B
C
N
O
F
Si
PS
ClAr
H
atomic number of element0 5 10 15 20
f
0
500 AlLi Na
2p3s
3p
3s
3p 2s
n = 2
3s
n = 3
2s
2p 10p+ n = 1
Al: 1s2 2s22p63s23p1
1s
Al
Al: 1s 2s 2p 3s 3p
3636S. Ensign, periodic properties
AlA filled s orbital provides some shielding of the nuclear charge felt by an electron in a p orbital of the same “n” value
Explanation of trend irregularities: N to O and P to S
2s
2p
2s
2p
2s 2s
1s 1s
O: 1s2 2s22p4N: 1s2 2s22p3
S. Ensign, periodic properties37
The e- configuration np3 (a “spin party”) is good
3p
Explanation of trend irregularities: N to O and P to S
3p
3s
p
3s
p
2s
2p
2s
2p
2s 2s
1s 1s
S: 1s2 2s22p63s23p4P: 1s2 2s22p63s23p3
S. Ensign, periodic properties38
The e- configuration np3 (a “spin party”) is good
Electron affinity (EA)y ( )• The energy change associated with the
addition of an electron to a gaseous atom gor ion
X+( )+ e- X( )
X(g) + e- X-(g)
• (-) E.A. : E is released (usually, but not always the case)
X (g)+ e X(g)
always the case)• (+) E.A. : E is added
When reported with units of kJ/mol, it is the energy change associated with adding one mol of electrons to one mol of gaseous atoms or ions
39
one mol of gaseous atoms or ions
39S. Ensign, periodic properties
Electron affinity values/trendsMore negative EA (in general) ex. n = 2, 5 and 8
nera
l)E
A (in
gen
hang
e in
Eot
muc
h ch
40
No
40S. Ensign, periodic properties
Why the trends in electron affinity values?
More negative EA (in general)
gen
eral
)
Z p+--
e in
EA
(in-
ch c
hang
eN
ot m
u
4141S. Ensign, periodic properties
Explanation for why group 2A elements have positive or small negative electron affinitiesg
2p3s
3p
2s
n = 2
3s
n = 3
10p+ n = 1
Add e-..
S. Ensign, periodic properties42Mg: 1s2 2s22p63s2
Explanation for why group 6A elements have positive or “out of pattern” negative electron affinities
2p 2p
2s
p
2s
p
e-
1s
N-: 1s2 2s22p4N: 1s2 2s22p3
1s
S. Ensign, periodic properties43
pp
The e- configuration np3 (a “spin party”) is good
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