Atomic structures cheat sheet
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This document provides an overview of atomic structure and electron configurations in chemistry. It defines key terms like atoms, electrons, energy levels, subshells and orbitals. It explains the organization of electrons according to the Aufbau principle, Hund's rule and Pauli exclusion principle. Electron configurations are represented using boxes and arrows, spectroscopic notation and noble gas notation. The document also discusses ion formations and exceptions to the rules, along with quantum numbers that describe electron location.
![AP Chemistry - Core Concept Cheat Sheet
12: Atomic Structures
Key Chemistry Terms
Boxes and Arrow Configurations
• Atom: smallest piece of matter that retains the chemical
properties of the element.
• Electron cloud: Area outside nucleus where electrons are
located.
• Energy levels: Electron cloud is divided into energy levels
for electrons.
• Subshells: Energy levels of electrons are divided into
subshells of equal energy orbitals.
• Orbitals: subdivision of subshell. Each orbital can hold 2
electrons.
• Valence electrons: The outermost shell.
• Isoelectric: Atoms of different elements with the same
electron configuration.
Atomic Structure
• Protons: Positive, in nucleus, 1 amu, determines the
identity of the atom.
• Neutrons: Neutral, in nucleus, 1 amu, atoms of the same
element with a different number of neutrons are isotopes.
• Electrons: Negative, outside nucleus, 0 amu, electrons
can be lost or gained to form an atom with a charge (ion).
Determining the number of electrons :
Atomic number = # of protons
Charge = protons - electrons
Energy Levels, Subshells and Orbitals
←
higher
energy
4 TYPES OF SUBSHELLS:
Subshell
s
p
d
f
Begins
in level
1
2
3
4
# of
orbitals
1
3
5
7
# of
electrons
2
6
10
14
Rules for Electron Configurations:
• Aufbau Principle: Electrons fill subshells in an order that
produces the lowest energy for the atom.
• Hund’s Rule: When filling orbitals, electrons are placed in
each equal-energy orbital before doubling up to produce
the lowest energy atom.
• Pauli Exclusion Principle: Two electrons occupying the
same orbital must be opposite spins (angular momentum).
Electron Configurations and the Periodic Table
Every element in a group of the periodic table has the same
number of electrons in the highest energy subshell.
Order of Filling for Subshells
Each orbital is shown with a box and each electron with an
arrow.
• Determine the number of electrons needed & follow the 3
rules governing electron configurations.
Example:
O (8 electrons): 1s ↑↓
2s ↑↓
2p ↑↓ ↑
↑
Spectroscopic Notation
Spectroscopic is a shorthand notation for electron
configurations.
• The number of electrons in each subshell is written as a
superscript after the subshell designation.
• The sum of the superscripts is equal to the total number of
electrons.
Example:
Br (35 electrons): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
Noble Gas Notation
Noble gases have full electron shells.
• The noble gas closest to the number of electrons needed
without going over is used to represent the core electrons.
• The spectroscopic notation is written for the valence
electrons.
Example:
Br (35 electrons): [Ar] 4s2 3d10 4p5
Electron Configuration of Ions
Most ions are formed from losing or gaining electrons to result
in a full valence shell.
Example:
Br1- (36 electrons): [Ar] 4s2 3d10 4p6
Exceptions to the Rules
A half-full “s” orbital and a “d” subshell with 5 or 10 are more
stable than following the Aufbau Principle.
Cr, Mo, W: s1 d5
Cu, Ag, Au: s1 d10
Quantum Numbers
Set of 4 numbers describing the location of an electron in an
Use the periodic table as a guide (read left to right):
atom.
1s
Name
Symbo
Describes
Found
Possibilities
2s
2p
l
3s
3p
Principal
Main energy
Shell #2
Whole # > 0
n
4s
3d
4p
energy
level
5s
4d
5p
level
6s
4f
5d
6p
Azimuthal
l
Subshell
s = 0, p = 1,
Whole # <n
number
shape
d = 2, f = 3
7s
5f
6d
7p
Magnetic
ml
Which
Number line
-l
+l
Or use the diagonal method:
orbital
system
1s
(middle is 0)
2s 2p
To read the chart, read down
+ or – ½
Spin
ms
Up or down
Up = + ½
3s 3p 3d
one diagonal as far as possible
Down = - ½
arrow
4s 4p 4d 4f
then jump to the top of the
5s 5p 5d 5f
next diagonal and repeat
Example:
6s 6p 6d
1s ↑↓ 2s ↑↓ 2p ↑↓ ↑ ↑
7s 7p
Quantum #’s for red arrow: 2, 1, -1, - ½
8s
How to Use This Cheat Sheet: These are the keys related this topic. Try to read through it carefully twice then rewrite it out on a
blank sheet of paper. Review it again before the exams.
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Atomic structures cheat sheet
- 1. AP Chemistry - Core Concept Cheat Sheet 12: Atomic Structures Key Chemistry Terms Boxes and Arrow Configurations • Atom: smallest piece of matter that retains the chemical properties of the element. • Electron cloud: Area outside nucleus where electrons are located. • Energy levels: Electron cloud is divided into energy levels for electrons. • Subshells: Energy levels of electrons are divided into subshells of equal energy orbitals. • Orbitals: subdivision of subshell. Each orbital can hold 2 electrons. • Valence electrons: The outermost shell. • Isoelectric: Atoms of different elements with the same electron configuration. Atomic Structure • Protons: Positive, in nucleus, 1 amu, determines the identity of the atom. • Neutrons: Neutral, in nucleus, 1 amu, atoms of the same element with a different number of neutrons are isotopes. • Electrons: Negative, outside nucleus, 0 amu, electrons can be lost or gained to form an atom with a charge (ion). Determining the number of electrons : Atomic number = # of protons Charge = protons - electrons Energy Levels, Subshells and Orbitals ← higher energy 4 TYPES OF SUBSHELLS: Subshell s p d f Begins in level 1 2 3 4 # of orbitals 1 3 5 7 # of electrons 2 6 10 14 Rules for Electron Configurations: • Aufbau Principle: Electrons fill subshells in an order that produces the lowest energy for the atom. • Hund’s Rule: When filling orbitals, electrons are placed in each equal-energy orbital before doubling up to produce the lowest energy atom. • Pauli Exclusion Principle: Two electrons occupying the same orbital must be opposite spins (angular momentum). Electron Configurations and the Periodic Table Every element in a group of the periodic table has the same number of electrons in the highest energy subshell. Order of Filling for Subshells Each orbital is shown with a box and each electron with an arrow. • Determine the number of electrons needed & follow the 3 rules governing electron configurations. Example: O (8 electrons): 1s ↑↓ 2s ↑↓ 2p ↑↓ ↑ ↑ Spectroscopic Notation Spectroscopic is a shorthand notation for electron configurations. • The number of electrons in each subshell is written as a superscript after the subshell designation. • The sum of the superscripts is equal to the total number of electrons. Example: Br (35 electrons): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 Noble Gas Notation Noble gases have full electron shells. • The noble gas closest to the number of electrons needed without going over is used to represent the core electrons. • The spectroscopic notation is written for the valence electrons. Example: Br (35 electrons): [Ar] 4s2 3d10 4p5 Electron Configuration of Ions Most ions are formed from losing or gaining electrons to result in a full valence shell. Example: Br1- (36 electrons): [Ar] 4s2 3d10 4p6 Exceptions to the Rules A half-full “s” orbital and a “d” subshell with 5 or 10 are more stable than following the Aufbau Principle. Cr, Mo, W: s1 d5 Cu, Ag, Au: s1 d10 Quantum Numbers Set of 4 numbers describing the location of an electron in an Use the periodic table as a guide (read left to right): atom. 1s Name Symbo Describes Found Possibilities 2s 2p l 3s 3p Principal Main energy Shell #2 Whole # > 0 n 4s 3d 4p energy level 5s 4d 5p level 6s 4f 5d 6p Azimuthal l Subshell s = 0, p = 1, Whole # <n number shape d = 2, f = 3 7s 5f 6d 7p Magnetic ml Which Number line -l +l Or use the diagonal method: orbital system 1s (middle is 0) 2s 2p To read the chart, read down + or – ½ Spin ms Up or down Up = + ½ 3s 3p 3d one diagonal as far as possible Down = - ½ arrow 4s 4p 4d 4f then jump to the top of the 5s 5p 5d 5f next diagonal and repeat Example: 6s 6p 6d 1s ↑↓ 2s ↑↓ 2p ↑↓ ↑ ↑ 7s 7p Quantum #’s for red arrow: 2, 1, -1, - ½ 8s How to Use This Cheat Sheet: These are the keys related this topic. Try to read through it carefully twice then rewrite it out on a blank sheet of paper. Review it again before the exams. RapidLearningCenter.com ©Rapid Learning Inc. All Rights Reserved