atomic structures
TRANSCRIPT
AP Chemistry Rapid Learning Series - 12
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Rapid Learning CenterChemistry :: Biology :: Physics :: Math
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Atomic Structure andAtomic Structure and Electron Configuration
AP Ch i t R id L i S i
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AP Chemistry Rapid Learning Series
Wayne Huang, PhDKelly Deters, PhDRussell Dahl, PhD
Elizabeth James, PhDDebbie Bilyen, M.A.
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Learning Objectives
Basic structure of atomsHow to determine the
By studying this tutorial you will learn…
How to determine the number of electronsHow to place electrons in energy levels, subshells and orbitalsHow to show electron configurations using three
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configurations using three methodsHow to write and understand Quantum Numbers
Concept Map
Chemistry
Studies
Previous content
New content
Matter
Studies
Atoms
Made of
Electrons
Quantum Numbers
Chemical properties determined by
Location described by
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Boxes and Arrows SpectroscopicNotation
Noble GasNotation
3 ways to show configurations
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Atomic Structure
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Definition: Atom
Atom Smallest piece of matter thatAtom - Smallest piece of matter that has the chemical properties of the element.
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Often called the“Building Block of Matter”
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What’s in an Atom?An atom is made of three sub-atomic particles.
Particle Location Mass
1
Charge
Nucleus
Nucleus
Outside the nucleus
1 amu = 1.67×10-27 kg
1 amu = 1.67×10-27 kg
0.00055 amu9.10×10-31 kg
+1
0
-1
Proton
Neutron
Electron
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1 amu (“atomic mass unit”) = 1.66 × 10-27 kg
The AtomNucleus Electron
cloud
M Very small relative mass
Charge = - (# of electrons)
Charge = # of protons
Mass = # of protons
+ # of neutrons
Overall Charge = # of protons
- (# of electrons)
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(# of electrons)
Overall Mass = # of protons
+ # of neutrons
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Protons Versus Electrons
Protons Electrons
+ Charge - Charge
Found in nucleus
# determines the “identity” of the atom
Found outside nucleus
# and configuration determine how the atom will react
Contributes to mass of atom
Does not contribute significantly to mass of atom
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Cannot be lost or gained without changing which element it is (nuclear reaction)The ratio of protons to electrons determines the charge on the atom.
Can be lost or gained—results in an atom with a charge (ion)
Electron Locations
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Definition: Electron Cloud
Electron cloud – It is the area outside ofthe area outside of the nucleus where the electrons reside.
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Electron Clouds
Electron cloud
Principle energy levels
Subshells
The electron cloud is made of energy levels.
Energy levels are
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Subshells
Orbitals
composed of subshells.
Subshells have orbitals.
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Definition: Subshell and Orbital
Subshell – A set of orbitals with equal energy.with equal energy.
Orbital – Area of probability of the electron being located.
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Each orbital can hold 2 electrons.
Types of Subshells
Begins inNumber of Total number
There are 4 types of subshells that electrons reside in under ordinary circumstances.
Subshell Begins in energy level
equal energy orbitals
of electrons possible
s
p 2
1
3
1
6
2
gy in
crea
ses
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d
f
3
4
5
7
10
14
Ener
g
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Pictures of Orbitals
s orbital
3 p orbitals
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5 d orbitals
Electron Configuration
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Definition: Electron Configurations
Electron Configurations –Shows the grouping and g p gposition of electrons in an atom.
Since the number of electrons and their configuration determines the chemical properties of the atom it is important to understand them
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of the atom, it is important to understand them.
Electron configurations use boxes for orbitals and arrow for electrons.
Aufbau Principle
Aufbau Principle: Electrons must fill subshells (and orbitals) so that the 1
The first of 3 rules that govern electron configurations:
( )total energy of atom is at a minimum.
1
What does this mean?
El t t fill th l t il bl b h ll
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Electrons must fill the lowest available subshells and orbitals before moving on to the next higher energy subshell/orbital.
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Energy and SubshellsThe energy diagram below shows the relative energy levels.
6p5d 4f
3s
4s
5s
3p
4p
5p
3d
4d
6s
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2s
2p
Ener
gy
Subshells are filled from the lowest energy level to increasing energy levels.
Not that this does not always go in numerical order.
Hund’s Rule
Hund’s Rule: Place electrons in unoccupied
The second of 3 rules that govern electron configurations.
Hund s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.
2
How does this work?
If you need to add 3 electrons to a p
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If you need to add 3 electrons to a p subshell, add 1 to each before beginning to double up.
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Pauli Exclusion Principle
Pauli Exclusion Principle: Two electrons that th bit l t h diff t i
3
The last of 3 rules that govern electron configurations.
occupy the same orbital must have different spins.
“Spin” describes the angular momentum of the electron
“Spin” is designated with an up or down arrow.
How does this work?
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How does this work?
If you need to add 4 electrons to a p subshell, you’ll need to double up. When you double up, make them opposite spins.
Determining the Number of ElectronsIn order to properly construct an electron configuration, you must be able to determine how many electrons to use.
Br1- Charge = -1
Charge = # of protons – # of electrons
Atomic number = # of protons
Example: How many electrons does the following have?
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-1 = 35 - electrons
Atomic number for Br = 35 = # of protons
Electrons = 36
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Another ExampleIn order to properly construct an electron configuration, you must be able to determine how many electrons to use.
No charge written Charge is 0Cl
Charge = # of protons – # of electrons
Atomic number = # of protons
Example: How many electrons does the following have?
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Electrons = 17
0 = 17 - electrons
Atomic number for Cl = 17 = # of protons
Applying the Rules
Aufbau Principle: Electrons must fill subshells (and orbitals) so that the total energy of atom is at a minimum.1
Use the 3 rules of electron configurations.
H d’ R l Pl l t i i d bit l f th
Example: Give the electron configuration for a Cl atom.
No charge written Charge is 0Cl
Pauli Exclusion Principle: Two electrons that occupy the same orbital must have different spins.3
Hund’s Rule: Place electrons in unoccupied orbitals of the same energy level before doubling up.2
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0 = 17 - electrons
No charge written Charge is 0ClAtomic number for Cl = 17 = # of protons
Electrons = 17
Place 17 electrons
1s 2s 2p 3s 3p
4231567910111213141516178
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Spectroscopic Notation
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Definition: Spectroscopic Notation
Spectroscopic Notation – Shorthand way of showing electron configurations.of showing electron configurations.
The number of electrons in a subshell are shown as a superscript after the subshell designation.
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1s 2s 2p 3s 3p
1s2 2s2 2p6 3s2 3p5
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Writing Spectroscopic NotationDetermine the number of electrons to place.1
Follow Aufbau’s Principle for filling order.2Fill in subshells until they reach their max (s = 2, p = 6, d = 10, f = 14).3The total of all the superscripts is equal to the number of electrons.4
Example: Give the spectroscopic notation for S.
No charge written Charge is 0S
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0 = 16 - electrons
No charge written Charge is 0SAtomic number for S = 16 = # of protons
Electrons = 16
Place 16 electrons
1s 2s 2p 3s 3p2 2 6 2 4
2 2 6 2 4+ + + + = 16
Electron Configurations and the Periodic Table
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1 2 2 2 2 5
Configurations Within a GroupLook at the electron configurations for the Halogens (Group 7).
F 1s2 2s2 2p5 F
Cl
Br
1s2 2s2 2p6 3s2 3p5
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
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I 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5
All of the elements in Group 7 end with 5 electrons in a p subshell.
Configurations and the Periodic TableIn fact, every Group ends with the same number of electrons in the highest energy subshell.Each area of the periodic table is referred to by the hi h t b h ll th t t i l t
s1 s2
p1 p2 p3 p4 p5 p6
highest energy subshell that contains electrons.
d-block
p-blocks-block
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d1 d2 d3 d4 d5 d6 d7 d8 d9 d10
p1 p2 p3 p4 p5 p6
f1 f2 f3 f4 f5 f6 f7 f8 f9 f10 f11 f12 f13 f14f-block
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Wondering how to remember the order of filling of the subshells? Just use the periodic table.
Periodic Table as a Road-Map
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In order to do this, the “f” block needs to be placed in atomic order.(It’s usually written below to fit it on the paper)
To see the filling order of subshells, read from left to right, top to bottom!
Periodic Table as a Road-Map
1s 1s
This tool shows that the 3d energy level is filled after the 4s energy level!
2p3p4p5p6p
3d4d5d6d
4f5f
1s2s3s4s5s6s7s
1s
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p subshells begin in level 2, so begin the p-block with “2p”
s subshells begin in level 1, so begin the s-block with “1s”
d subshells begin in level 3, so begin the d-block with “3d”f subshells begin in level 4, so begin the f-block with “4f”
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Another Tool for Filling Order
1s To read the charge,
There is another tool commonly used to remember orbital filling order.
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
To read the charge, move down one diagonal as far as possible, then jump to the top of the next diagonal and keep going.
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5s 5p 5d 5f
6s 6p 6d
7s 7p
8s
ElectronElectron Configurations of Ions
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Definition: Ion
Ion – an atom that has gained or lost electrons gresulting in a net charge.
Atoms gain and lose electrons to be in a more stable state.
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Usually, the “more stable state” is a full valence shell.
Outermost shell of electrons
Look at the electron configurations for the following:
Full Valence Shell Ions
1s 2s 2p2 2 6
Br-1
O2-
1s 2s 2p 3s 3p2 2 6 2 6 4s 2 3d 10 4p 6
p = 35 -1 = 35 - e e = 36
p = 8 -2 = 8 - e e = 10
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Na+
Ca2+
1s 2s 2p 3s 3p2 2 6 2 6
p = 11 +1 = 11 - e e = 10
p = 20 +2 = 20 - e e = 18
1s 2s 2p2 2 6
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What do you notice about each of these configurations?
Full Valence Shell Ions
They all end with full p subshells.
Notice that O2- and Na+ have the same number and configuration of
1s 2s 2p2 2 6
Br-1
O2-
1s 2s 2p 3s 3p2 2 6 2 6 4s 2 3d 10 4p 6
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electrons.Na+
Ca2+
1s 2s 2p 3s 3p2 2 6 2 6
1s 2s 2p2 2 6 This makes them isoelectric.
Noble Gas Configuration
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Definition: Noble Gas Notation
Noble Gas – Group 8 of the Periodic Table. They contain full valence shells.
Noble Gas Notation – Noble gas is used to represent the core (inner) electrons and only the valence shell is shown.
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1s 2s 2p 3s 3p2 2 6 2 6 4s 2 3d 10 4p 5
4s 2 3d 10 4p 5[Ar]
Br
Spectroscopic
Noble gas
The “[Ar]” represents the core electrons and only the valence electrons are shown.
How do you know which noble gas to use to symbolize the core electrons?
Which Noble Gas Do You Choose?
Think: Price is Right.
H d i th P i i Ri ht?How do you win on the Price is Right?
By getting as close as possible without going over.
Choose the noble gas that’s closest without going over!
Noble Gas # of electrons
He 2
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Ne
Ar
Kr
Xe
10
18
36
54
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How do you know where to start off after using a noble gas?Use the periodic table!
Where Does the Noble Gas Leave Off?
2p3p4p5p6p
3d4d5d6d
4f5f
1s2s3s4s5s6s7s
HeNeArKrXeRn
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6d5f7s
The noble gas fills the subshell that it’s at the end of.
Begin filling with the “s” subshell in the next row to show valence electrons.
Noble Gas Notation ExampleDetermine the number of electrons to place.1
Determine which noble gas to use.2Start where the noble gas left off and write spectroscopic notation for the valence electrons.3
Example: Give the noble gas notation for As.
No charge written Charge is 0As
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0 = 33 - electrons
As Atomic number for As = 33 = # of protons
Electrons = 33 Place 33 electrons
[Ar] 4s 3d 4p2 10 3 18 2 10 3+ + = 33
Closest noble gas: Ar (18) Ar is full up through 3p
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Comparing the Different Notations
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Pros and Cons of Each NotationEach notation has it’s advantages and disadvantages.
Pro Con
Shows if electrons are paired or unpaired
Quicker than “Boxes and arrows”
Longest method
Does not show pairing of electrons
“Boxes and arrows”
Spectroscopic notation
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Allows focus on the valence electrons (that control bonding)Quickest method
Does not show core electrons
Does not show pairing of electrons
Noble Gas notation
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Exceptions to the Aufbau Rule
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Stability of d Subshells with 5 or 10d subshells have 5 orbitals…They can hold 10 electrons.
According to the Aufbau principle, Cr should have the following valence electron configuration:
4s2 3d4
But a half-full or completely full d subshell is more stable than the above configuration, so it is:
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4s1 3d5
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Elements with ExceptionsThe following elements are excepts to the Aufbau Principle:
Element Should be Actually is
4s2 3d4
5s2 4d4
6s2 5d4
4s2 3d9
5s2 4d9
4s1 3d5
5s1 4d5
6s1 5d5
4s1 3d10
5s1 4d10
Cr
Mo
W
Cu
Ag
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g
6s2 5d9 6s1 5d10Au
They are the two groups on the periodic table that begin with Cr and Cu.
Quantum Numbers
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Definition: Quantum Numbers
Quantum Numbers – A set of 4 numbers that describes the electron’s placement in the atom.
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4 Quantum Numbers
2, 1, -1, + ½
n ml
Quantum Number
Symbol
n
Describes
Shell number
S b h ll
Possible Numbers
Whole #s ≥ 1Principal
l ms
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l
ml
ms
Subshell type Whole # < n
- l + l
+ ½ or – ½
Azimuthal
Magnetic
Spin
Orbital
Spin
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Determining Quantum Numbersn: principal energy level
l: subshell s = 0
Give the number of the shell
4p 3
l: subshell s = 0p = 1d = 2f = 3
ml: orbital 0s -1 0 1p -2 -1 0 1 2d
-3 -2 -1 0 1 2 3f
coding system
Number-line system of identifying orbitals.0 is always in the middle.Number line from l to + l
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Number line from – l to + l
ms: spin
Coding system
↑= + ½ ↓ = - ½
Quantum Number ExamplesGive the quantum numbers for the red arrow.Example:
1s 2s 2p 3s 3p
It’s in level “3” 0It s in level 3
___, ___, ___, ___3
It’s in subshell “s”—the “code” for “s” is “0”
0It’s in orbital “0”
0It’s a down arrow - ½
Give the quantum numbers for the red arrow.Example:
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1s 2s 2p 3s 3p
It’s in level “2”
___, ___, ___, ___2
It’s in subshell “p”—the “code” for “p” is “1”
1It’s in orbital “-1”
-1It’s an up arrow + ½
-1 0 +1
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Identifying Incorrect Quantum Numbers
Example: What’s wrong with the following sets of quantum numbers?
1, 1, 0, + ½ n = 1…OK as n (energy level) can be any whole # > 0l = 1…subshell is “p”
There is no p subshell in energy level 1
2, 1, -2, - ½
There is no p subshell in energy level 1
n = 2…OK as n can be any whole # >0l = 1…subshell is “p”
OK as level 2 has “p”ml = -2…on the “-2” orbital
“p” subshell has 3 orbitals: ___ ___ ___-1 0 +1
No “-2” orbital in a “p” subshell. ml must be between –l and l
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1, 0, 0, -1
ml must be between l and l
n = 1…OK as n can be any whole # >0l = 0…subshell is “s”
OK as level 1 has an “s”ml = 0…on the “0” orbital
OK as “s” has 1 orbital and it’s “0”ms = -1
ms must be either + ½ or – ½
Atomic Structure & The AP Exam
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Atomic Structure in the Exam
How many paired or unpaired electrons are in an t f l t?
Common atomic structure problems:
atom of an element?
Given a set of quantum numbers, what’s the next higher level or sublevel?
When shown a set of boxes & arrows, which element is it?
Is a set of quantum numbers possible?
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Is a set of quantum numbers possible?
This topic isn’t used in the Free Response section very often…usually just the multiple choice!
Multiple Choice QuestionsThe first few questions on the AP MC exam give a list of choices and then ask several questions about that same list.
A. SeB. MgC. AlD. NE. F
1. The atom that contains exactly 2 unpaired electrons
Example: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
1s2 2s2 2p6 3s2
1s2 2s2 2p6 3s2 3p1
1s2 2s2 2p3
1s2 2s2 2p5
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2. The atom that contains exactly 2 electrons in the highest occupied subshell
3. The atom that must obtain 3 electrons to obtain a full subshell
A. Se (4 e-1 in the p subshell means 2 are unpaired)
B. Mg
D. N (if a p has 3, it needs 3 more to be full)
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Another Multiple Choice Question
Example: Which of the following atoms is in an excited state?
A. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4
B 1s2 2s2 2p6 3s2 3p2B. 1s2 2s2 2p6 3s2 3p2
C. 1s2 2s2 2p6 3s2 3p2 4s1
D. 1s2 2s2 2p6 3s2 3p6 4s2 3d8
E. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
An atom in an excited state is one in which an electron has been promoted to a higher subshell.
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p g
Option “C” has an electrons in the 4s subshell when the 3p isn’t full—this shows a promoted electron.
Answer: C
Electron configurations can
be shown with
Electron configurations can
be shown with
Atoms are made of protons, neutrons
and electrons. The configuration of the
Atoms are made of protons, neutrons
and electrons. The configuration of the
Quantum numbersdescribe the
location of an
Quantum numbersdescribe the
location of an
Learning Summary
Electron configurations Electron configurations
boxes and arrows, in spectroscopic notation, or noble
gas notation.
boxes and arrows, in spectroscopic notation, or noble
gas notation.
gelectrons
determines the chemical properties
of the atom.
gelectrons
determines the chemical properties
of the atom.
ocat o o aelectron in an atom and are a series of
4 numbers.
ocat o o aelectron in an atom and are a series of
4 numbers.
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gare written following the Aufbau principle, Hund’s Rule and the
Pauli Exclusion Principle.
gare written following the Aufbau principle, Hund’s Rule and the
Pauli Exclusion Principle.
Electrons are organized in levels,
subshells and orbitals.
Electrons are organized in levels,
subshells and orbitals.
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Congratulations
You have successfully completed the core tutorial
Atomic Structure and Electron ConfigurationElectron Configuration
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