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October 10, 2016
ATOMIC STRUCTURE Table of Contents
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• The Bohr Model
The Bohr Model
• Quantum Mechanics
• The Quantum Model
• Energy Level Diagrams and Electron Configurations
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of Contents
Table of Contents
Bohr Model
The Problem with the Nuclear Atom
Democritus Dalton Thomson Rutherford We have established so far:
460 BC
1803
1897
1912
1. Atoms are made of protons, neutrons, and electrons.
?
2. Protons and neutrons make up the mass of an atom and are found together in the small, dense nucleus.
3. The electrons are found outside the nucleus and occupy the vast majority of the volume. Atomos
Dalton's
Plum Nuclear
Postulates
Pudding
Model
Question: What are some problems with this model?
Model
Evolution of Theory
Atomic Model
Answer
Evolution of Atomic Theory Positive and negative ch
attract, so why aren't electrons and protons tog
Why don't the electrons "
the nucleus?
October 10, 2016
The Problem with the Nuclear Model
The Problem with the Nuclear Model
2. Only when energized, atoms do emit energy. A continuous spectrum is not produced; instead, an emission spectrum of only specific wavelengths and frequencies is produced. This is also referred to as a line spectrum. 1. Most atoms are stable and do not release energy at all. If electrons were continuously orbiting the nucleus in uniform circular motion, like the Nuclear model predicted, they would be accelerating; accelerating charges release energy as a continuous spectrum. e­
External energy added
(electricity, light, etc.)
emits energy
e­
e­
light energy
emitted
Emission Spectrum
continuous spectrum
nucleus
Observations
Observations
1 When atoms are energized by electricity, what is observed?
2 Why was the Nuclear Model insufficient?
Answer
B It could not account for the stability of the atom
A A continuous spectrum of light B
C It required the electrons to be in the nucleus and the protons in orbit around the nucleus D A and B
B An emission spectrum of specific colors only.
C Neither a nor b
Question
Question
Answer
A It could not explain the existence of emission spectra
D
October 10, 2016
Emission Spectra and the Bohr Model
Niels Bohr interpreted these observations and created a new model of the atom that explained the existence of emission spectra and provided a framework for where the electrons can exist around the nucleus.
Emission Spectra and the Bohr Model
Bohr knew that the wavelengths seen in the emission spectra of hydrogen had a regular pattern. Each series was named after the scientist who observed these particular spectral lines. Lyman Series
(spectral lines in the UV range)
Balmer Series
(spectral lines in the visible and UV range)
Paschen Series (spectral lines in the infrared range)
Emission Spectra
Emission Spectra and the Bohr Model
Bohr proposed that electrons could orbit the nucleus, like planets orbit the sun...but only in certain specific orbits.
Emission Spectra
Emission Spectra and the Bohr Model
Each orbit would correspond to a different energy level for the electron, designated by "n"
n = 3
n = Increasing energy
2
n =
1
+
Emission Spectra
Emission Spectra
October 10, 2016
Emission Spectra and the Bohr Model
The Bohr Atom
The lowest energy level is called the ground state; the others are excited states.
Bohr reasoned that each spectral line was being produced by an electron moving from a high energy orbit to a lower energy orbit, and giving off energy in the form of light.
Hydrogen atom
n = 4
n = 3
n
n = 2
5
4
3
n = 1
+
2
1
Since only certain frequencies of light were produced, only certain orbits must be possible.
Bohr Atom
Emission Spectra
Emission Spectra and the Bohr Model
The energy of each orbit is quantized­­only certain values were possible. The emission spectrum could be explained as movment of electrons from a higher energy orbit to a lower energy orbit.
3 According to Bohr, "n" stands for...
A the number of cycles
C the energy level of the orbit
D the number of orbits
upper
e­
lower
Emission Spectra
e­
upper
lower
Question
Answer
B the number of electrons
C
October 10, 2016
4 In the Bohr model of the atom an electron in its lowest energy state
5 Which of the following best explains why excited atoms produce emission spectra and not continuous spectra?
Answer
B is farthest from the nucleus
C is in an excited state
D emits energy
A
B A continuous spectrum requires the movement of neutrons
C Electrons can only exist in certain stable orbitals of specific energies
D Electrons can exist and move anywhere around the nucleus and are not bound to a specific orbit
Question
Question
Emission Spectra and the Bohr Model
Emission Spectra and the Bohr Model
According to Bohr's model, electrons can absorb energy and move from a lower energy orbital to a higher energy orbital. An excited electron can release energy and move down to any lower energy orbital. The energy that the electron either absorbs or emits must equal the difference between the two energy levels of the orbitals involved. n = 4
n = 3
n = 2
n = 1
+
Here we see 2 separate emissions coming from the same electron. The electron can either go from n=3 right to n=1 or it can go from n=3 to n=2 to n=1. n = 2
n = 2
n = 1
+
Both are acceptable and both will occur.
Emission Spectra
n = 4
n = 3
n = 4
n = 3
photon
Emission Spectra
n = 1
+
Answer
A Not all atoms contain enough electrons to produce a continuous spectrum
A is in the ground state
C
October 10, 2016
Emission Spectrum of Hydrogen
Emission Spectra and the Bohr Model
Hydrogen atoms have one proton and one electron. The emission spectrum of hydrogen shows all of the different possible wavelengths of visible light emitted when an excited electron returns to a lower energy state. Transition
light emitted The difference in energy between neighboring orbits decreases as one moves farther from the nucleus. E = hν c = λν
n = 3
6 2
4
2
3.03 x 10­19
2 ­­> 1
122 1.63 x 10­18
Transition
n = 1
486 nm
+
+
3 2
3 ­­> 2
wavelength of spectral line produced (nm)
656
n = 2
410 nm
Energy (J)
656 nm
Click here for Bohr model animation
Hydrogen
Emission Spectra
Emission Spectra and the Bohr Model
6 Which of the following electron transitions would produce the highest energy spectral line? The energy differences between the Bohr orbits were found to match exactly the energy of a particular spectral lines in the emission spectra of Hydrogen. n = 1
­19
Energy of n = 3 = ­2.417 x 10
J
B 3 ­­> 2
Energy of n = 2 = ­5.445 x 10­19 J
n
+
­19
­19
∆E = (­2.417 x 10 J) ­ (­5.445 x 10 J) ­19
∆E = 3.028 x 10 J
C 4 ­­> 3
5
4
3
2
D 2 ­­> 1
Hydrogen emission spectrum
1
Red line wavelength (λ)= 656.3 nm
E = hf or E = hc/λ
E = 3.0 x 10­19 J
Emission Spectra
Question
Answer
n = 2
A 5 ­­> 4
Notes
n = 3
D
October 10, 2016
Emission Spectra and the Bohr Model
Emission Spectra and the Bohr Model
Due to the differing numbers electrons, atoms of each element produce a unique emission spectrum after being energized. The emission spectrums can be used to identify the presence of a particular element. Emission spectrum of Iron
Emission Spectra
Since electrons can only move between orbits of set energies atoms must absorb energy at the same frequencies at which they emit energy. As a result, monitoring which frequencies of light are absorbed can help us determine which element or molecule is present. Absorption
Emission Spectra
7
The emission spectrum for Chlorine is shown below. Which of the following represents Chlorine's corresponding absorption spectrum? A
B
Answer
Absorption vs. Emission
Answer
Below are the visible wavelength emission spectra for hydrogen and iron. What difference do you notice about the two spectra? Propose a reason for this difference. Emission spectrum of Hydrogen
C Question
October 10, 2016
9 Which of the following is NOT true regarding the Bohr model of the atom?
Does the picture below illustrate a photon emission or absorption?
n = 4
n = 3
B
n = 2
Emission
A Electrons could exist only in certain quantized orbits around the atom
n = 1
Absorbtion
+
C Neither
D Both
B As "n" becomes greater, the energy of the orbit is greater also
C When returning from an excited state, an electron can can only move between the set Bohr orbits
D All of these are true
Question
Question Rutherford vs Bohr Model Quantum Mechanics
The Bohr model could only explain the emission spectrum of hydrogen with one electron. It could not adequately the behavior of atoms with more than one electron. Return to Table
of Contents
Aug 9­9:05 PM
Quantum Mechanics
Answer
A
Answer
8
D
October 10, 2016
THE PROBLEM WITH THE BOHR MODEL
Bohr’s model could only describe the behavior of a hydrogen atom, which only has one electron. The Bohr model could not explain the emission spectra of atoms with more than one electron. Scientists needed to find a new way to explain how electrons are arranged around the nucleus. Bohr model of a hydrogen atom
QUANTUM MECHANICS Quantum mechanics was a major breakthrough that helped scientists better understand the atom in a way that classical physics could not do. Scientists first tried to use classical physics to explain how electrons are arranged—but it could not explain the behavior of subatomic particles like electrons. Feb 22­4:27 PM
THE QUANTUM MECHANICAL MODEL Erwin Schrödinger helped improve our understanding of the atomic model. He combined the following concepts: (1) First, electrons are particles, but they also act like waves (remember de Broglie proposed that matter can act like a wave). Feb 22­4:28 PM
10 It is possible to know the exact path of an electron.
True False (2) Second, scientists could not accurately predict where a particle, like the electron, is and its momentum at the same time—this is referred to as the Heisenberg uncertainty principle. Scientists could only determine the probability of an electron being in a certain area around the nucleus. Answer
The Schrödinger Wave Equation. This equation is used to determine the probability of finding an electron in a certain area around the nucleus.
Feb 22­4:28 PM
Question
False
October 10, 2016
uncertainty principle.
C
photoelectric effect.
D
principle of relativity.
Answer
B
Question
C
remain the same.
D
be uncertain.
Question
remain the same.
D
be uncertain.
THE QUANTUM MECHANICAL MODEL The quantum mechanical model of an atom treats the electron as both a wave and a particle. Instead of predicting definite paths the electron travels in—like the Bohr model—
the quantum mechanical model predicts the probable location of finding an electron. Answer
decrease.
decrease.
C
Question
13 If the accuracy in measuring the momentum of a particle increases, the accuracy in measuring its position will
A increase.
B
B
B
Feb 22­4:28 PM
Answer
12 If the accuracy in measuring the position of a particle increases, the accuracy in measuring its momentum will A increase.
11 The idea that the position and momentum of an electron cannot measured with infinite precision is referred to as the A exclusion principle.
October 10, 2016
Bohr Model vs Quantum Mechanical QUANTUM NUMBERS Quantum numbers (n, l, ml, ms) are used to describe the probable location of finding an electron in an orbital
. NOTE: No two electrons in an atom may have the same set of quantum numbers. n = the energy level of the orbital; the energy level is also referred to as a shell
l = the shape of the orbital, (s,p,d,f)
ml = the orientation of the orbital in space
ms = the direction of the electron spin How many quantum numbers are used to describe the probable location of an individual electron? Feb 22­4:32 PM
Aug 9­9:05 PM
15 Quantum mechanics allows to you predict exactly what an electron will due.
14 Quantum mechanics provides a mathematical definition for the: A wave­like properties of electrons only.
B particle­like properties of electrons only
True Question
Answer
D the wave­particle duality of electrons
Answer
False C classic Newtonian forces that govern atoms
D
Question
False
October 10, 2016
Quantum­Mechanical Model of the Atom
Since we can't say exactly where an electron is, the Bohr model, with electrons in neat orbits, can't be correct. Quantum theory describes an electron probability distribution; this figure shows the distribution for the ground state of hydrogen.
The Quantum Model
In this picture, the probability of finding an electron somewhere is represented by the density of dots at that location.
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The Quantum Model
Quantum View of Atoms
Quantum Numbers
Solutions to Schrodinger's Wave Equation take the form of sets of numbers. There are four different quantum numbers: n, l, ml, ms needed to specify the state or probable location of an electron in an atom.
n = principal
l = angular
ml = magnetic
ms = spin
n = 4
Orbitals An orbital is a region of space where an electron is most likely to be found. Note: A maximum of two electrons can be found in each orbital. Y
n = 3
n = 2
n = 1
+
X
Z
energy level/
distance from nucleus
shape
of orbital
orientation of orbital in space
Quantum Numbers
­
+
direction of
electron spin
Aug 9­9:52 PM
October 10, 2016
(n): Principal Quantum Number 16 The principal quantum number, n, determines the ____________ of the orbital. n = 4
The principal quantum number, n, describes the energy level of the orbital, often called the energy shell. The values of n are integers greater than or equal to 1:
n ≥ 1
n = 3
n = 2
n = 1
A
Orientation
B
Energy
C
Shape
D
Capacity
+
Answer
In general, the larger the value of n, the farther from the nucleus the electron should be found.
Principal Quantum Number
Question
17 As n increases, the orbital energy _________ .
Each orbital region has a very specific shape based on the energy of the electrons occupying them and a specific orientation in space.
Increases
B
Decreases
(l): Angular Quantum Number C
Remains constant
Quantum number l designates the shape of the orbital.
D
Increases then decreases
Answer
A
There are four shapes of orbitals: s,p,d,f
(ml): Magnetic Quantum Number Quantum number ml designates the orientation of the orbital in space.
Question
Angular & Magnetic Numbers
October 10, 2016
Electron Orbital Shape and Orientations
The s orbital
s orbitals are spherical in shape.The radius of the sphere increases with the value of n.
If you are looking for an electron in an s orbital, the direction you look in doesn't really matter,
they have only one orientation in space.
1
1
2
2
If l = s shape ml = 1 orientation
1 orbital per energy level http://chemwiki.ucdavis.edu/@api/deki/files/4826/=Single_electron_orbitals.jpg
Orbital Shape
s Subshell
The p orbital
p orbitals have two lobes with a node between them.
The p orbitals come in a set of three, each at a different orientation in space. l = p shape ml = 3 orientations
3 orbitals per energy level p Subshell
The d orbital
High probability of finding an electron
d orbitals have more complex shapes. There are 5 possible orientations in space, so there are 5 possible d orbitals. Low probability of finding an electron
l = d shape ml = 5 orientations
5 orbitals per energy level
d Subshell
3
3
October 10, 2016
The f orbital
There are 7 possible f orbitals. # of orbitals
# of electrons
s
p
d
f
l = f shape ml = 7 orientations
7 orbitals per energy level
f Subshell
Aug 12­12:31 PM
19 The magnetic quantum number, m , determines 18 The quantum number, l, determines the ____________ of the orbital. B
Energy
C
Shape
D
Capacity
Question
A
Orientation
B
Energy
C
Shape
D
Capacity
Answer
Orientation
Answer
A
l
the ____________ of the orbital.
Question
October 10, 2016
20 A(n) ___ orbital is lobe­shaped
21 An s orbital has ______ possible orientations in s
A
1
B
p
B
3
C
d
C
5
D
f
D
7
Answer
A
Question
Answer
space.
Question
Spin Quantum Number, m
22 An f orbital has ______ possible orientations in s
A
1
B
3
C
5
D
7
Answer
space.
The spin quantum number can be positive or negative.
This implies that electrons are in some way able to pair up, even though they repel each other due to the electromagnetic force. Each orbital can therefore hold maximum of 2 electrons that must spin in the opposite directions.
­ spin
Question
Spin Number
+ spin
A
October 10, 2016
can only have two values
A
the same spin
B
relates to the spin of the electron
B
no spin
C
relates to the spin of the atom
C
opposite spins
D
Both A & B
D
electrons cannot occupy the same orbital
Answer
A
Question
Question
Energy Levels and Sublevels
Quantum Numbers Subshells
Some combinations of Quantum Numbers are impossible:
For example, you don't find p, d, or f orbital in the first energy level. Orbitals with the same value of n form a shell.
Different orbital types within a shell are subshells.
n subshell # of orbitals total # total # of orbitals of electrons
1 1s 1 1 2
2 2s 1 2p 3 4 8
3 3s 1
3p 3
3d 5 9 18
4 4s 1
4p 3
4d 5 4f 7 16 32
Energy Levels & Sublevels
Quantum Number Subshells
Answer
24 Electrons within the same orbital must have
23 The spin quantum number, ms October 10, 2016
25 If n = 1 an electron can occupy which of the subshells? A
1s
2p
D
3s
A
Answer
C
2
Answer
2s
Answer
B
26 n = 1 can hold a maximum of ___ electrons
6
Click here for an electron orbital game.
Question
Question
27 What is the maximum number of electrons 28 An electron is in the 6f state. Determine the principal quantum number. Answer
that can occupy the n = 4 shell? Question
32
Question
October 10, 2016
29 An electron is in the 6d state. How many Energies of Orbitals
electrons are allowed in this state? 10
For example: the energy of 4s is less than the energy of 3d.
7d
6f
7
6
7p
6d
5f
7s
6p
5d
Energy
Answer
7f
Notice that some sublevels on a given n level may have less energy than sublevels on a lower n level. 5
6s
5p
4
5s
3
4s
2
3s
1
2s
4f
4d
4p
3d
3p
2p
1s
Question
Feb 3­10:30 AM
Energy Level Diagram / Orbital Diagrams
Orbital diagrams are a way to illustrate the energy levels of electrons.
Each box in the diagram represents one orbital.
Energy Level Diagrams &
Electron Configurations
Arrows represent the electrons.
The direction of the arrow represents the relative spin of the electron (+ or ­).
8
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of Contents
Electron Configurations
O
1s 2s 2p
Orbital Diagrams
October 10, 2016
Energies of Orbitals
Electron Orbital Diagram
30 In an electron orbital diagram, an individual box represents? A Energy level Orbital diagrams can also be drawn vertically to illustrate increasing energy. B Orbital C The electron To complete an orbital diagram you must first know how many electrons the atom has. D The electron spin In a neutral atom:
# of electrons = # of protons
so the # of electrons will be the same as the atomic number.
6
C
Energies of Orbitals
31 In an electron orbital diagram, which symbol represents an electron? A
B
Question
32 In an electron orbital diagram, the three orbitals together indicate each orbital occupies
A The same energy level
B The same electrons
C C Different energy levels
D both B and C
D Different electron spins
Question
Question
October 10, 2016
3 Rules for Filling Electron Orbitals
Aufbau Principle
Aufbau Principle
Electrons are added one at a time to the lowest energy orbitals available until all the electrons of the atoms have been accounted for. Aufbau takes its name from a German word meaning "building up". Pauli Exclusion Principle
Electrons fill the lowest energy orbitals first.
An orbital can hold a maximum of two electrons. To occupy the same orbital, two electrons must spin in the opposite direction. Hund's Rule
One electron is placed in each of the equal energy orbitals (set of 3 p's, set of 5 d's, etc) before a second electron is added. 3 Rules
Aufbau
Hund’s Rule
Pauli Exclusion Principle
Two electrons in the same orbital must have opposite spins. The up arrow is always written first. correct
1s2
2s2
Every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin.
incorrect
correct
2p1
1s2
2s2
2p2
1s2
2s2 2p2
incorrect
Think about the Empty Bus Seat Rule. People will not sit next to each other on a bus until all the seats are taken up
1s2
2s2 2p1
Pauli Exclusion
Hunds
October 10, 2016
Answer
Fill in the Energy Level Diagram for Magnesium, Mg.
Fill in the Energy Level Diagram for Chlorine, Cl.
Practice
Practice
Energy Level Diagram 33 The orbital diagram below depicts electrons in which element? Fill in the Energy Level Diagram for Iron, Fe.
Answer
A Oxygen B Sodium C Aluminum D Iron Practice
Question
Answer
Energy Level Diagram Energy Level Diagram October 10, 2016
34 The orbital diagram below depicts electrons in which element? A Boron
B Carbon 35 What is wrong with the electron orbital diagram below?
A Electrons are not filling lower energy orbitals first ­ violation of the Aufbau Principle. B Two electrons occupying the same orbital have the same spin ­ violation of the Pauli Exclusion Principle. C Nitrogen
D Neon
C Some orbitals are double occupied by electrons before every orbital has at least one electron ­ violation of Hund's Rule. D This orbital diagram is correct. Question
Question
36 What is wrong with the electron orbital diagram below?
37 What is wrong with the electron orbital diagram below?
A Electrons are not filling lower energy orbitals first ­ violation of the Aufbau Principle. A Electrons are not filling lower energy orbitals first ­ violation of the Aufbau Principle. B Two electrons occupying the same orbital have the same spin ­ violation of the Pauli Exclusion Principle. B Two electrons occupying the same orbital have the same spin ­ violation of the Pauli Exclusion Principle. C Some orbitals are double occupied by electrons before every orbital has at least one electron ­ violation of Hund's Rule. C Some orbitals are double occupied by electrons before every orbital has at least one electron ­ violation of Hund's Rule. D This orbital diagram is correct. D This orbital diagram is correct. Question
Question
October 10, 2016
38 What is wrong with the electron orbital diagram below?
39 What is wrong with the electron orbital diagram below?
A Electrons are not filling lower energy orbitals first ­ violation of the Aufbau Principle. A Electrons are not filling lower energy orbitals first ­ violation of the Aufbau Principle. B Two electrons occupying the same orbital have the same spin ­ violation of the Pauli Exclusion Principle. B Two electrons occupying the same orbital have the same spin ­ violation of the Pauli Exclusion Principle. C Some orbitals are double occupied by electrons before every orbital has at least one electron ­ violation of Hund's Rule. C Some orbitals are double occupied by electrons before every orbital has at least one electron ­ violation of Hund's Rule. D This orbital diagram is correct. D This orbital diagram is correct. Question
Electron Configurations
Question
Electron Configurations
Electron configurations show the distribution of all electrons in an atom.
Electron configurations show the distribution of all electrons in an atom.
Each component consists of:
Each component consists of:
A number denoting the shell
A number denoting the shell,
A letter denoting the type of subshell
Electron Configurations
Electron Configurations
October 10, 2016
Electron Configuration of Sodium
Electron Configurations
For example, the ground­state configuration of sodium is:
Electron configurations show the distribution of all electrons in an atom.
Each component consists of:
2
1s2 2s
2p6 3s1
Slide • A number denoting the shell,
• A letter denoting the type of subshell, and • A superscript denoting the number of electrons in those orbitals.
Check Your Work: All of the superscript numbers add up to the total number of electrons. 23
11
Na
Sodium Atom
Remember in a neutral atom the # of electrons = # of protons
Electron Configurations
Electron Configuration of Na
Practice
Practice
Write the Ground State Electron Configuration
for Phosphorous, P.
Electron Configuration
Write the Ground State Electron Configuration
for Calcium, Ca.
Practice
Answer
Answer
Electron Configuration
1s22s22p63s23p3
Practice
1s22s22p63s
October 10, 2016
Practice
Practice
Write the Ground State Electron Configuration
for Titanium, Ti.
Write the Ground State Electron Configuration
for Bromine, Br.
1s22s22p63s23p64s23d2
Answer
Answer
Electron Configuration
Practice
Practice
40 What is the electron configuration for Li ? A
1s3
B
1s1 2s2
D
1s2 1p1
B 1s22s23s23p6
Question
C 1s22s22p6
D 1s22s22p63s23p64s1
Question
Answer
1s2 2s1
A 1s22s23s23p64s2
Answer
C
41 Which of the following is the correct electron configuration for Potassium (K)? 1s22s22p63s23p64
October 10, 2016
42 A neutral atom has an electron configuration of 1s 2s 2p 3s 3p1. What is its atomic number? A 5
B
11
C
13
D
20
6
43 A neutral atom has the following electron configuration: 1s2 2s2 2p6 3s2 3p64s23d104p3. What element is this? 2
A zinz
B copper
C arsenic
D germanium
Question
C
D
1s22s32p6
none of the given answers
Question
Question
*
Energy Level Diagram ­ Excited State
Answer
44 A neutral atom has an electron configuration of 1s2 2s2 2p6 . If a neutral atom gains one additional electron, what is the ground state configuration? A 1s22s22p63s1
B 1s22s22p7
Answer
2
Answer
2
In a sodium­vapor lamp electrons in sodium atoms are excited to the 3p level by an electrical discharge and emit yellow light as they return to the ground state. Excited State
Na Excited State Energy Level Diagram
October 10, 2016
*
*
46 Which of the following represents an excited state electron configuration for Magnesium (Mg)? 1s22s22p63s1
A
1s22s22p63s2
B
1s22s22p7
B
1s22s22p73s1
C
1s22s22p63p1
C
1s22s22p63s13p1
D
none of the given answers
D
none of the above
Answer
A
Question
Question
Paired and Unpaired Electrons
When two electrons occupy the same orbital, they are called paired electrons. When a single electron is by itself, it is an unpaired electron. EXAMPLE: 1s22s22p63s23p1
Aluminum has one unpaired electron. Sep 6­4:35 PM
Answer
45 Which of the following represents an excited state electron configuration for Sodium (Na)? Attachments
=Single_electron_orbitals.webloc