chapter 7
DESCRIPTION
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 (m l ). Pauli’s Exclusion Principle. discovered in 1925 by Wolfgang Pauli - PowerPoint PPT PresentationTRANSCRIPT
Electrons in atoms are arranged as:
Shells (n)
Subshells (l)
Subshell orientation (ml)
Arrangement of Electrons in Atoms
Practice: What are the 4 quantum numbers for each electron in He?
discovered in 1925 by Wolfgang Pauli
-No two electrons in an atom can have the same set of 4 quantum numbers
Pauli’s Exclusion Principle
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
11 s
value of nvalue of l
no. of
electrons
Example: H atomic number = 1
Two ways to express electron configuration:
1. spdf notation
Writing Electron Configurations
Arrowsdepictelectronspin
ORBITAL BOX NOTATIONfor He, atomic number = 2
1s
21 s
Arrowsdepictelectronspin
ORBITAL BOX NOTATIONfor He, atomic number = 2
1s
21 s
2. Orbital box notation
spdf notation
Writing Electron Configurations
Electron ConfigurationsUsing the Aufbau Principle to determine the
electronic configurations of the elements
1st row elements:
22
11
1s He
1s H
ionConfigurat 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
NeAr
Ne Cl
Ne S
Ne P
Ne Si
3p s3 Ne Ne Al
s3 Ne Ne Mg
s3 Ne Ne Na
ionConfigurat 3p 3s
18
17
16
15
14
1213
212
111
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
111 s3 Ne NeNa
ionConfigurat 3p 3s
Electron Configurations and Quantum Numbers
electron s 31/2 0 0 3 e 11
electrons p 2
1/2 1 1 2 e 10
1/2 0 1 2 e 9
1/2 1 1 2 e 8
1/2 1 1 2 e 7
1/2 0 1 2 e 6
1/2 1- 1 2 e 5
electrons s 21/2 0 0 2 e 4
1/2 0 0 2 e 3
electrons s 11/2 0 0 1 e 2
1/2 0 0 1 e 1
m m n
-th
-th
-th
-th
-th
-th
-th
-th
-rd
-nd
-st
s
l l
The ml and ms are interchangeable
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-
220 4s Ar [Ar]Ca
ionConfigurat 4p 4s 3d
Skip the first 18 electrons
electrons s 41/2 0 0 4 e 20
1/2 0 0 4 e 19]Ar[
m m n
-th
-th
s
l l
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
6226 3d 4s Ar Ar Fe
ionConfigurat 4p 4s 3d
Electron Configurations and Quantum Numbers
Electrons are removed from subshell of highest energy level (n-level)
P0 [Ne] 3s2 3p3 -3e- ---> P3+ [Ne] 3s2 3p0
1s
2s
3s3p
2p
1s
2s
3s3p
2p
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
Electron Configurations of Ions
To form cations, always remove electrons of highest n value first!
More About the Periodic Table
Representative ElementsGroups 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-to-bottom
More About the Periodic Table
d-Transition ElementsAll have d electrons
-With n s-orbitals -With n-1 d–orbitals
Have small property variations from row-to-row
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 1s2
Ne [He] 2s2 2p6
Ar [Ne] 3s2 3p6
Kr [Ar] 4s2 4p6
Xe [Kr] 5s2 5p6
Rn [Xe] 6s2 6p6
Periodic PropertiesPeriodic 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 PropertiesElectronegativity: 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+ ionAtom(g) + energy Atom+
(g) + e-
Example: 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+ + e-
Mg+ + 1451 kJ/mol Mg2+ + e-
- Atoms can have 3rd (IE3), 4th (IE4), etc. - Each IE is significantly higher than the
previous IE
Periodic PropertiesIonization Energy:
1. IE2 > IE1
always takes more energy to remove a second electron from an ion
2. IE1 increases to the rightImportant exceptions are Be & Mg, N & P, etc. due to filled and half-filled subshells
3. IE1 decrease down
First Ionization Energies
0
500
1000
1500
2000
2500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Atomic Number
Ionization Energy (kJ/mol)
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
AlSi
P
S
Cl
Ar
K
Ca
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 ionSign 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
Mg(g) + e- + 231 kJ/mol Mg-(g)
EA = +231 kJ/mol
Examples of electron affinity values:
Increasing ability to add electrons
decre
asin
g a
bilit
y
to a
dd
ele
ctr
on
s
Br(g) + e- Br-(g) + 323 kJ/mol
EA = -323 kJ/mol
Electron Affinities of Some Elements
-400-350-300-250-200-150-100-50
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Atomic Number
Ele
ctro
n A
ffin
ity
(kJ/
mo
l)
Electron Affinity
H
He
Li
Be B
C
N
O
F
NeNa
Mg Al
Si
P
S
Cl
ArK
Ca
Periodic Properties
Example: Arrange these elements based on their electron affinities:Al, Mg, Si, Na
Si < Al < Na < Mg
Periodic PropertiesIonic Radius: diameter of an atom in its ionized form
-Cations are always smaller
Element Li Be
Atomic Radius (Å)
1.52 1.12
Ion Li+ Be2+
Ionic Radius (Å)
0.90 0.59
Periodic Properties
Anions are always larger
Element N O F
AtomicRadius(Å)
0.75 0.73 0.72
Ion N3- O2- F1-
IonicRadius(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+
IonicRadii(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-
IonicRadii(Å)
1.71 1.26 1.19
Periodic Properties
Example: Arrange these elements based on their ionic radii:
Ca2+, K+, Ga3+
K1+ > Ca2+ > Ga3+