Transcript Chapter 8
Chapter 7
The Structure of Atoms and
Periodic Trends
Arrangement of Electrons in Atoms
Electrons in atoms are arranged as:
Shells (n)
Subshells (l)
Subshell orientation (ml)
Pauli’s Exclusion Principle
discovered in 1925 by Wolfgang Pauli
-No two electrons in an atom can have the same
set of 4 quantum numbers
Practice: What are the 4 quantum numbers for
each electron in He?
Aufbau Principle
Describes the electron filling order in atoms
-electrons are placed in the lowest available energy
orbital
-the periodic table is a
function of electron
configurations for the
elements
Electron Configuration
To remember the correct filling order for
electrons in atoms:
Electron Configuration
Writing Electron Configurations
Two ways to express electron configuration:
1. spdf notation
Example: H atomic number = 1
1s
1
no. of
electrons
value of l
value of n
Writing Electron Configurations
2. Orbital box notation
ORBITAL BOX NOTATION
for He, atomic number = 2
spdf notation
2
1s
1s
Arrows
depict
electron
spin
Electron Configurations
Using the Aufbau Principle to determine the
electronic configurations of the elements
1st row elements:
1s
1
H
2
He
Configuration
1
1s
2
1s
Electron Configurations
Hund’s rule: electrons
fill suborbitals by
placing electrons in
each suborbital
unpaired first with the
same spin direction,
then the electrons pair
Electron Configurations
3s
3p
Configuration
11 Na Ne
12
Mg Ne
13
Al
14
Si
15
P
16
S
17
Cl
18
Ar
Ne
Ne
Ne
Ne
Ne
Ne
Ne 3s1
Ne 3s 2
Ne 3s 2 3p1
Electron Configurations and Quantum
Numbers
We can write a complete set of quantum
numbers for all of the electrons in every
element:
– Na
– Ca
– Fe
3s
11 Na Ne
3p
Configuration
Ne 3s1
Electron Configurations and Quantum
Numbers
n
l
ml
1
0
0
2 nd e - 1
0
0
3rd e -
2
0
0
4 th e -
2
0
0
5th e-
2
1
6 th e -
2
1
7 th e -
2
1
8th e-
2
1
9 th e -
2
1
10th e -
2
1
11th e -
3
0
1st e -
ms
1/2
1 s elect rons
1/2
1/2
2 s elect rons
1/2
1/2
0
1/2
1 1/2
2 p elect rons
1 1/2
The ml and ms are interchangeable
0
1/2
1 1/2
0
1/23 s elect ron
-1
Electron Configurations and Quantum
Numbers
Noble Gas Notation (or short hand notation):
The first 18 electrons in Ca are represented with the
preceding noble gas ([Ar])
- we only concern ourselves with the outermost e-
3d
20 Ca [Ar]
4s
4p
Configuration
Ar 4s2
Skip the first 18 electrons
Electron Configurations and Quantum
Numbers
n
l
ml
[Ar]19th e -
4
0
0
20th e -
4
0
0
ms
1/2
4 s elect rons
1/2
Electron Configurations and Quantum
Numbers
There is only one set of 4 quantum numbers for each of
the 26 electrons in Fe:
– To save space, we use the symbol [Ar] to represent the first
18 electrons in Fe
3d
26 Fe Ar
4s
4p
Configuration
Ar 4s2 3d6
Electron Configurations of Ions
Electrons are removed from subshell of
highest energy level (n-level)
P0 [Ne] 3s2 3p3
-3e- ---> P3+ [Ne] 3s2 3p0
3p
3p
3s
3s
2p
2p
2s
2s
1s
1s
Electron Configurations of Ions
For transition metals, remove the highest
s-orbital electrons first:
Fe [Ar] 4s2 3d6
-2 electrons
Fe2+ [Ar] 3d6
-3 electrons
Fe3+ [Ar] 3d5
To form cations, always remove electrons of highest n value first!
More About the Periodic Table
Representative Elements
Groups IA, IIA, IIIA-VIIIA
– These elements will have
their “outermost” electron
in an outer s or p orbital
– Variations in their properties
are similar from top-tobottom
More About the Periodic Table
d-Transition Elements
All have d electrons
-With n s-orbitals
-With n-1 d–orbitals
Have small property
variations from row-torow
More About the Periodic Table
f - transition metals
-Sometimes called inner
transition metals
-Electrons are being
added to f orbitals
Extremely small variations in
properties from one element
to another
More About the Periodic Table
Noble Gases
-Have filled electron shells
-have similar chemical reactivities
-similar electronic structures
He
Ne
Ar
Kr
Xe
Rn
1s2
[He] 2s2 2p6
[Ne] 3s2 3p6
[Ar] 4s2 4p6
[Kr] 5s2 5p6
[Xe] 6s2 6p6
Periodic Properties
• Atomic radii describes the relative sizes of atoms
• Atomic radii increase within
a column
• Atomic radii decrease within
a row
Periodic Properties
Example: Arrange these elements based on their
atomic radii:
Se, S, O, Te
O < S < Se < Te
Periodic Properties
Example: Arrange these elements based on their
atomic radii:
P, Cl, S, Si
Cl < S < P < Si
Periodic Properties
Electronegativity: measure of the tendency of an
atom to attract electrons to itself
-Fluorine is the most electronegative element
-Cesium is the least electronegative element
Electronegativity increase from left-to-right and
decrease from top-to-bottom
increase
decrease
Periodic Properties
Example: Arrange these elements based on their
electronegativity:
Se, Ge, Br, As
Ge < As < Se < Br
Periodic Properties
Example: Arrange these elements based on their
electronegativity:
Be, Mg, Ca, Ba
Ba < Ca < Mg < Be
Periodic Properties
Ionization Energy: energy required to remove
an electron from an atom in the gas state
First ionization energy (IE1)
– Energy required to remove the first electron from an
atom in the gas state to form a 1+ ion
Atom(g) + energy Atom+(g) + eExample:
Mg(g) + 738kJ/mol Mg+ + e-
Periodic Properties
Second ionization energy (IE2)
– The amount of energy required to remove
the second electron from a gaseous 1+ ion
Atom+ + energy Atom2+ + eMg+ + 1451 kJ/mol Mg2+ + e- Atoms can have 3rd (IE3), 4th (IE4), etc.
- Each IE is significantly higher than the
previous IE
Periodic Properties
Ionization Energy:
1. IE2 > IE1
always takes more energy to remove a second
electron from an ion
2. IE1 increases to the right
Important exceptions are Be & Mg, N & P, etc. due to
filled and half-filled subshells
3. IE1 decrease down
First Ionization Energies
He
2500
Ne
2000
Ionization
Energy
(kJ/mol)
N
1500
1000
H
C
Be
F
Ar
Cl
P
O
Mg
S
B
500
Li
Ca
Si
Na
Al
K
0
1 2
3 4
5 6 7
8 9 10 11 12 13 14 15 16 17 18 19 20
Atomic Number
Periodic Properties
Example: Arrange these elements based on their
first ionization energies:
Sr, Be, Ca, Mg
Sr < Ca < Mg < Be
Periodic Properties
Example: Arrange these elements based on their
first ionization energies:
Al, Cl, Na, P
Na < Al < P < Cl
Periodic Properties
Electron Affinity: Energy absorbed when an
electron is added to an atom to form a negative
ion
Sign conventions for electron affinity:
– If electron affinity > 0 energy is absorbed
– If electron affinity < 0 energy is released
Electron affinity is the measure of an atom’s
ability to form negative ions
atom(g) + e- + EA
atom-(g)
Periodic Properties
Examples of electron affinity values:
Mg(g) + e- + 231 kJ/mol Mg-(g)
EA = +231 kJ/mol
Br(g) + e- Br-(g) + 323 kJ/mol
EA = -323 kJ/mol
Increasing ability to
decreasing ability
to add electrons
add electrons
Electron Affinity
Electron Affinities of Some Elements
Electron Affinity (kJ/mol)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
0
-50
-100
-150
-200
-250
-300
-350
-400
He
Be
B
N
Ne
Mg
Al
Ar
P
Na
H
Li
K
O
C
Si
S
F
Atomic Number
Ca
Cl
Periodic Properties
Example: Arrange these elements based on their
electron affinities:
Al, Mg, Si, Na
Si < Al < Na < Mg
Periodic Properties
Ionic Radius: diameter of an atom in its ionized form
-Cations are always smaller
Element
Atomic
Radius (Å)
Ion
Ionic
Radius (Å)
Li
Be
1.52
1.12
Li+
Be2+
0.90
0.59
Periodic Properties
Anions are always larger
Element
N
O
F
Atomic
Radius(Å)
Ion
0.75
0.73
0.72
N3-
O2-
F1-
Ionic
Radius(Å)
1.71
1.26
1.19
Periodic Properties
Cation radii decrease from left to right across a
period
– Increasing nuclear charge attracts the electrons and
decreases the radius.
Ion
Rb+
Sr2+
In3+
Ionic
Radii(Å)
1.66
1.32
0.94
Periodic Properties
Anion radii decrease from left to right across a
period
– Increasing electron numbers in highly charged ions
cause the electrons to repel and increase the ionic
radius
Ion
N3-
O2-
F1-
Ionic
Radii(Å)
1.71
1.26
1.19
Ionic Radii
Active Figure 8.15
Periodic Properties
Example: Arrange these elements based on their
ionic radii:
Ca2+, K+, Ga3+
K1+ > Ca2+ > Ga3+
Periodic Properties
Example: Arrange these elements based on their
ionic radii:
Cl-1, Se-2, Br-1, S-2
Cl1- < S2- < Br1- < Se2-