Energy Levels of Electrons
Bohrs idea of quantized energy levels does have
parallels in quantum mechanics.
For example, quantum mechanics predicts discrete,
quantized principal energy levels for electrons in
an atom.
Principal energy level (n):
provides a general idea of the
distance
of an electron from the nucleus
(as n increases, so does the
distance
from the nucleus)
n can be a positive integer (1,2,3,
etc.)
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Energy Levels of Electrons
Each energy level can be divided into sublevels.
Each sublevel corresponds to a different type
of orbital that can house electrons.
Principal quantum level n =1
Contains only one sublevel/orbital (1s orbital)
The orbital is spherical in nature,
as are all s orbitals.
The orbital is a space where an electron
has a
90% probability of being located.
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Energy Levels of Electrons
How many electrons can fit in an orbital?
Pauli Exclusion Principle: an atomic orbital can hold
two
electrons, which must have opposite spins.
Electron spin is represented by arrows(
or )
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Energy Levels of Electrons
Principal quantum level n =2
Contains two sublevels/orbitals (2s and 2p orbitals)
The 2s orbital is spherical like a 1s orbital,
but larger and higher in energy.
The 2p sublevel consists of three orbitals: px, py
and pz.
The shape of the 3 orbitals is the same;
they differ in their orientation in space.
6 total electrons can occupy the 3 p orbitals of a
subshell.
Each p orbital
has two lobes.
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Energy Levels of Electrons
Principal quantum level n =3
Contains three sublevels/orbitals (3s, 3p and 3d
orbitals)
The 5 3d orbitals have unique shapes relative
to s and p orbitals.
10 total electrons can occupy the
5 d orbitals of a subshell.
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Energy Levels of Electrons
With each new principal quantum level,
a new sublevel/orbital type is introduced.
Quantum Level Summary
Principal Quantum
Level (n)
Sublevels
1s
_____
_____
_____
2s
2p 2p 2p
_____
_____
3s
3p 3p 3p
3d 3d 3d 3d 3d
_____
4s
4p 4p 4p
4d 4d 4d 4d 4d
4f 4f 4f 4f 4f 4f 4f
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2014 John Wiley & Sons, Inc. All rights reserved.
Energy Levels of Electrons
Practice
What is the maximum number of electrons
in a 4d sublevel?
a. 2
b. 4
c. 6
d. 10
Any d sublevel has 5 total orbitals.
Two electrons can be housed in each
orbital.
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Energy Levels of Electrons
Practice
What is the maximum number of electrons that can
occupy the n = 3 sublevel?
a. 8
b. 2
c. 18
d. 10
The n = 3 sublevel has 3 types of
orbitals:
s (1), p (3), and d (5).
Two electrons can occupy each orbital.
(9 x 2 = 18)
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Atomic Structure of the First 18
Elements
Hydrogen: consists of a nucleus with one proton
and one electron in a 1s orbital.
How are electrons treated in more complicated
atoms
thatmultielectron
contain multiple
electrons?
Assuming
atoms
have orbitals
similar to that of the hydrogen atom,
rules for filling electrons can be developed.
Guidelines for filling electrons:
1. Only up to two electrons can occupy an orbital.
2. Electron will occupy lower energy orbitals first.
Orbital energies: s < p < d < f for a given n value.
3. Each orbital in a sublevel must contain an electron
before another electron can be added to any of the
orbitals.
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Atomic Structure of the First 18
Elements
Three ways of depicting atomic and electronic
structure:Diagrams
I) Atomic Structure
Depict both the nuclear and electronic structure
II) Electron configuration
Each orbital is listed, in order of increasing energy,
while depicting the number of electrons in
each orbital/sublevel.
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Atomic Structure of the First 18
Elements
Three ways of depicting atomic and electronic
structure:
III) Orbital Diagram
Boxes represent orbitals and electron spins
are represented as arrows.
3p
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Atomic Structure of the First 18
Elements
Helium
Hydrogen
1s1
1s2
1s
1s
Electron
Orbital Diagram configuration
Orbital Diagram
Lithium
Berylium
1s22s2
1s22s1
1s
2s
Electron
configuration
1s
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2s
Atomic Structure of the First 18
Elements
Filling the p subshell
Boron
1s22s22p1
1s
2s
2p
Carbon
1s22s22p2
1s
2s
2p
Note the electrons are in different orbitals per Rule
3.
The similar
spin
will
be
discussed
shortly.
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John Wiley
& Sons,
Inc. All
rights reserved.
Atomic Structure of the First 18
Elements
Filling the p subshell
Nitrogen
1s22s22p3
1s
2s
2p
Note the electrons are in different orbitals per Rule
3.
Oxygen
1s22s22p4
1s
2s
2p
Two electrons must be paired in one p orbital.
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Atomic Structure of the First 18
Elements
Filling the p subshell
Fluorine
1s22s22p5
1s
2s
2p
Neon
1s22s22p6
1s
2s
2p
All electrons are paired in the p shell.
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Atomic Structure of the First 18
Elements
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Atomic Structure of the First 18
Elements
Beyond Ne
Sodium
1s22s22p63s1
1s
2s
2p
3s
Begin filling the 3n shell.
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Atomic Structure of the First 18
Elements
Valence Electrons:
electrons located in the highest energy
(outermost) orbitals of an atom.
Example
Oxygen
Electron configuration
1s22s22p4
Outermost valence electrons are in the n =2
subshell;
oxygen has 6 total valence electrons.
The column number (1A-7A) in the periodic table
gives the valence electrons of an element.
Valence electrons participate in bonding to form
molecular compounds (see Chapter 11).
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Electronic Configuration Practice
How many valence electrons does phosphorus
contain?
a. 5
b. 8
c. 15
d. 18
P is in Group 5A.
It will contain 5 valence electrons.
Electron Configuration
1s22s22p63s23p3
Valence electrons
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Electronic Configuration Practice
Which element could have the following
electron configuration?
a. Cl
b. Ca
c. Ar
d. S
1s22s22p63s23p6
The element contains 18 electrons.
It must also contain 18 protons.
Atomic number 18 = argon.
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Electron Structures and the
Periodic Table
How does the electronic structure of atoms relate
to their
positioning on the periodic table?
Origins of the Periodic Table
Mendeleev and Meyer proposed organizing elements
based on increasing atomic masses.
Their ideas formed the origins of the modern
periodic table.
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The Modern Periodic Table
columns (groups/families):
elements with similar
properties.
rows
(periods):
increasing
Z
(atomic
number)
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The Modern Periodic Table
Period number corresponds to the highest
principal quantum number n of the elements.
Group numbering: by numbers 118 or
with numbers/letters (i.e., 7A).
A groups are the representative elements.
B groups are the transition elements.
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The Modern Periodic Table
Alkali
Metals
Main Group
Halogen
Alkaline
s
Earths
Transition
Metals
Main Group
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Noble
Gases
Periodic Table Practice
Magnesium is a member of what group of
elements?
a. Halogens
b. Noble gases
c. Alkali metals
d. Alkaline earth metals
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The Modern Periodic Table
Group Commonalities: All elements in a group
have similar valence electron configurations.
This often leads to similar reactivity
of elements in a group.
Because electron configurations of larger elements
are
very long, a shorthand notation is used that
highlights valence electrons.
Example
Na [Ne]3s1
This indicates the electron configuration of sodium
is that for Ne with an additional 3s1 electron.
The shorthand electron configuration always uses
the
previous noble gas core with the valence electrons
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John element
Wiley & Sons, Inc. All
rights
reserved.
for
the
of
interest.
Electron Filling
Initially, one may expect to fill 3d electrons
before 4s electrons.
However, based on reactivity of the elements K and
Ca,
they resemble metals with valence electrons in s
Example
K orbitals.
[Ar]4s1
Ca
[Ar]4s2
Elements 21-30 are transition elements where
electrons now fill in the 3d subshell.
Once the 3d subshell is filled, the 4p shell begins to
fill.
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Electron Filling
Sublevel Filling Diagram
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Electron Filling Practice
The electron configuration [Ar] 4s1 is the
ground state electron configuration of:
a. K
b. P
c. Fluorine
d. Na
The element contains 1 valence
electron
in the fourth period (due to n = 4).
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Electron Filling Practice
The electron configuration [Ne] 3s23p1, is the
ground state electron configuration of:
a. Na
b. Al
c. Ar
d. S
The element contains 3 valence
electrons
in the third period (due to n = 3).
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Chemical Periodicity
Groups of elements show similar chemical
properties
because of similarities in their valence electrons.
Group number equals the total number of
outermost valence electrons.
Example Group 7 contains the
ns2np5 valence configuration
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Learning Objectives
10.1 Electromagnetic Radiation
List the 3 basic characteristics of electromagnetic
radiation
10.2 The Bohr Atom
Explain the relationship between the line spectrum
and the quantized energy levels of an electron in an
atom.
10.3 Energy Levels of Electrons
Describe the principal energy levels,
sublevels and orbitals of an atom.
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Learning Objectives
10.4 Atomic Structure of the First 18 Elements
Use the guidelines to write electron configurations.
10.5 Electron Structures and the Periodic Table
Describe how the electron configurations of the
atoms
relate to their position on the periodic table and
write electron configurations for elements based
on their position on the periodic table.
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