Electron Configuration
SOL: CH. 2 g, i
Textbook pages: 126-146; 187-188; 639-644
Workbook pages: 43-49; 224-225 Section (20.2 only)
(valence electrons Lewis Dot Diagram and octet rule)
SOL for the Units
Virginia Standard: CH.2 g, i
• The student will investigate and understand that the placement of
elements on the periodic table is a function of their atomic structure. The
periodic table is a tool used for the investigations.
Key Concepts:
• g. electron configurations, valence electrons, and oxidation numbers.
• i. historical and quantum models.
Essential Understandings:
• Electron configuration is the arrangement of electrons around the nucleus
of an atom based on their energy level.
• Atoms can gain, lose, or share electrons within the outer energy level.
• Discoveries and insights related to its structure have changed the model of
the atom over time.
• The modern atomic theory is called the Quantum Mechanical Model.
Flame Test
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Fireworks originated in China about 2000
years ago.
– Legends states a Chinese alchemist
who mixed charcoal, sulfur, and
potassium nitrate accidently
produced a colorful gunpowder.
Using the flame test lab it is relatively
easy to obtain the colorful flames
associated with fireworks.
In the flame test the METAL atom is
associated with a specific color. Ex:
LiCl2 and Li2SO4 compounds produce
red flame but BaCl2 and BaSO4
compounds produce green flames.
– However, the nonmetal (Cl) atom
atom in these compounds do not
seem to affect the color of the
compound. Ex: LiCl2 and BaCl2 do
not have the same color.
Flame test is a quick method used to
confirm the presence of certain metal
atoms in an unknown sample.
The temperature of the flame is high
enough to excite the electrons but not
change the nuclei of the atom.
How Flame Test Works
Using Bohr Model of the Atom
•
He used the term energy levels (or shells) to describe
these orbits of differing energy. He said that the
energy of an electron is quantized, meaning electrons
can have one energy level or another but nothing in
between.
• The energy level an electron normally occupies is
called its ground state. But it can move to a higherenergy, less-stable level, or shell, by absorbing
energy. This higher-energy, less-stable state is called
the electron’s excited state.
• After it’s done being excited, the electron can return
to its original ground state by releasing the energy it
has absorbed, as shown in the diagram.
• Sometimes the energy released by electrons occupies
the portion of the electromagnetic spectrum (the
range of wavelengths of energy) that humans detect
as visible light.
– Slight variations in the amount of the energy are
seen as light of different colors. The light that is
seen is known as the atomic emission
spectrum. (See next slide)
Electromagnetic Spectrum
•Wavelength and frequency are inversely related.
•Gamma rays have shortest wavelength (highest frequency) and radio waves
have the longest wavelength (lowest frequency).
•Visible light wavelength is between 400 nm to 700 nm. The only region of the
electromagnetic spectrum humans can see.
•The speed of light equation is used to show the relationship between
wavlength and frequency.
Wave Characteristics
• Amplitude - height of the
wave. Determines the
brightness or intensity of
light.
• Wavelength -distance
between crest of the wave.
A full wave cycle is one
complete upward and
downward motion.
Measured in m or nm.
• Frequency - the time it
takes for a wave to finish 1
full cycle. Measured in s-1
or Hz.
• Speed-rate at which wave
moves =3.00 x 108 m/sec
c = λν
Speed of light equation
Atomic Spectrum for Hydrogen
Why is the emission spectrum always the same?
• When a hydrogen atom is excited it gives off light. However, only certain colors are
shown and is called the atomic emission sprectrum.
• This spectrum is unique for all atoms.
• Each line in the spectra corresponds to one exact frequency (wavelength) of light that
is emitted from the element.
• Planck’s proposed there is a fundamental restriction on how much
energy an object can absorb or emit.
– These pieces of energy are called quantum (fixed amount.)
– Contradicts old classical physics that an object can absorb and emit
any amount of energy.
• Planck’s fundamental equation shows the relationship between
frequency (and also wavelength) of a particular radiation and with which
it is associated.
E=h v
– E = Energy
– h = Planck’s constant, 6.626 x 10-34 J.s
– v = frequency
– c = speed of light
–  = wavelength
• Because h is a constant value it shows that E and v are directly
proportional. So the larger amount of E released the the greater the
frequency.
• Albert Einstein recognized that Planck’s theory and equation could be
used to explain the PHOTOELECTRIC EFFECT.
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In the photoelectric effect electrons are ejected from the surface of a meal when light
shines on the metal.
Every metal has a minimum frequency of light needed to release electrons.
– Red light, regardless of the it’s intensity or amount of time it radiates metal surface,
can’t produce photoelectric effect with potassium metal.
– However, a green or violet light shining on surface of K metal could cause the
photoelectric effect.
Einstein proposed that light consists of quanta of energy he called photons.
Photons strike the metal surface and it’s energy is transferred to the metal’s electrons.
The electron will only “swallow” the photon if it has the right amount of energy.
– Electron can’t use just a portion of the energy from a photon, and it can’t collect
energy from several photons.
– If photon energy is too small the electron won’t have enough energy to escape from
the metal.
Therefore the energy (thus frequency) and not the number of photons (light intensity) is
relevant in the photoelectric effect.
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Understanding locations of electrons in the atom helps to explain many of the unique
properties each atom possesses.
The QUANTUM MECHANICAL MODEL of the atom determines the allowed energies an
electron can have and how likely it is to find the electron in various locations around the
nucleus.
– Comes from the mathematical solutions to the Schrodinger equation.
This model looks at the probability of finding an electron within a certain volume of space
surrounding the nucleus and is represented by a fuzzy cloud.
– The cloud is more dense where probability of finding electrons is high.
– The cloud is less dense where probability of finding electrons is low.
KNOW IT IS TIME TO LEARN THE PARTS OF THE QUANTUM MECHANICAL MODEL.
Electron Configuration Rules
• Aufbau Principle - electrons occupy the
orbitals of lowest energy first. Once this energy
level is filled the electrons will start to occupy
the next lowest energy level.
• Pauli Exclusion Principle - atomic orbitals can
hold a maximum of two electrons and the
electrons must have opposite spin.
• Hund’s Rule - electrons occupy orbitals of the
same energy in a way that makes the number
of electrons with the same spin as large as
possible.
Electron Configuration Filling Orbital
Hund’s Rule
Pauli Exclusion Principle
Some Additional Terms…
• Abbreviated electron (shorthand configuration)shorthand notation describing the distribution of electrons
among the energy levels of an atom. This notation makes it
easier to focus on the valence electrons, pg 170 old
textbook.
• Lewis Dot structure (electron dot structure)- a notation
that displays valence electrons as dots around the atomic
symbol. Symbol represents inner core electrons and the
atomic nucleus, pg 188.
• Octet rule- atoms will lose, gain, or share their valence
electrons to have eight valence electrons like the noble
gases, pg 188.
• Quantum of energy- amount of energy needed to move an
electron from one level to another.
• Valence electrons- number electrons on the outermost
(highest occupied) energy level, pp187-188.
Oxidation Numbers
Oxidation Number (Oxidation State) 
The charge that an atom would have if the
electrons in the bond were possessed entirely
by the more electronegative element.
Example:
HCl is covalent (no charges) {H :Cl}
H+ Cl+1
-1 are the “apparent charges”
Oxidation numbers serve as a bookkeeping
tool used to keep track of electron movement.
Assigning Oxidation Numbers
1.
2.
3.
4.
5.
All pure elements and homogeneous molecules = 0
Elements in group IA = +1
Elements in group IIA = +2
Ag+, Zn+2, Al+3
In binary compounds the second element = anion
charge
6. Oxygen is almost always = -2
7. Hydrogen is almost always = +1
8. The total charge of a compound is always = 0
A Sample Problem
What are the oxidation numbers of the
elements in Na2SO4?
Na = +1 (times 2 atoms) = +2
O = -2 (times 4 atoms) = -8
+2 + -8 = -6
If the compound must = 0, then S must =
+6
Give the oxidation number for:
1.
2.
3.
4.
5.
6.
7.
8.
S
Mn
N
C
N
S
S
Fe
in Na2SO3
in KMnO4
in Ca(NO3)2
in Na2CO3
in NO2in SO4-2
in H2S2O7
in Fe(C2H3O2)2
Speed of Light
Answer to Practice Problems page 140 and
150.
#14= 2.00x10-5m (longer than red light)
#15= 6.00 x 1015m (ultraviolet)
#54= 2.61 x 1014cm (hint: pay attention to your units.)
#55
a) 4.36x10-5cm b) visible c) 6.88x 1014s-1.
#56
a) 5.890 x10-5cm & 5.896x10-5cm
b) 5.090 x 1014s-1 & 5.084 x 1014s-1.
c)yellow light
Practice Problems using Planck’s Equation
1. A particular photon of light has an energy of 3.25 x10-16
J. What is the frequency of the light?
2. When sodium is heated, a yellow spectral line whose
energy is 3.37 x 10-19 J is produced. (a) What is the
frequency? (b) What is the wavelength?
Answers:
1. 4.90 x 1017 s-1.
2. (a) 5.09 x 1014 s-1. (b) 5.89 x 10-7 m.