This document provides an activity sheet on the electronic structure of atoms for General Chemistry 1. It contains background information on orbital diagrams and how to draw them according to Aufbau principle, Pauli's exclusion principle, and Hund's rule. The activity sheet has two activities: 1) completing tables to write electron configurations and draw orbital diagrams for elements and 2) writing abbreviated electron configurations and determining unpaired electrons for given elements. It also provides an answer key and links to additional references.

1. i
General Chemistry 1
Activity Sheet
Quarter 2 – MELC 3
Week 2
Electronic Structure of Atoms
REGION VI - WESTERN VISAYAS
SHS

2. ii
Development Team of STEM Activity Sheet
Writer: Russel V. Apiladas
Editor: Moonyeen C. Rivera
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Analie J. Lobaton.
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Regional Management Team
Ma. Gemma M. Ledesma,
Dr. Josilyn S. Solana,
Dr. Elena P. Gonzaga,
Mr. Donald T. Genine,
Rovel R. Salcedo,
Moonyeen C. Rivera,
Anita S. Gubalane,
Minda L. Soldevilla,
Daisy L. Lopez,
Joseph M. Pagalaran
General Chemistry 1
Activity Sheet No. 3: Electronic Structure of Atoms
First Edition, 2020
Published in the Philippines
By the Department of Education
Region 6 – Western Visayas
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Introductory Message
Welcome to General Chemistry 1!
The Learning Activity Sheet is a product of the collaborative efforts of the
Schools Division of Cadiz and DepEd Regional Office VI - Western Visayas through
the Curriculum and Learning Management Division (CLMD). This is developed to
guide the learning facilitators (teachers, parents and responsible adults) in helping the
learners meet the standards set by the K to 12 Basic Education Curriculum.
The Learning Activity Sheet is self-directed instructional materials aimed to
guide the learners in accomplishing activities at their own pace and time using the
contextualized resources in the community. This will also assist the learners in
acquiring the lifelong learning skills, knowledge and attitudes for productivity and
employment.
For learning facilitator:
The General Chemistry 1 Activity Sheet will help you facilitate the leaching-
learning activities specified in each Most Essential Learning Competency (MELC)
with minimal or no face-to-face encounter between you and learner. This will be
made available to the learners with the references/links to ease the independent
learning.
For the learner:
The General Chemistry 1 Activity Sheet is developed to help you continue
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meaningful and engaging activities for independent learning. Being an active learner,
carefully read and understand the instructions then perform the activities and answer
the assessments. This will be returned to your facilitator on the agreed schedule.

5. 1
Name of Learner: ____________________________________________________
Grade and Section: __________________________________ Date: ___________
General Chemistry 1 Activity Sheet No. 3
Electronic Structure of Atoms
I. Learning Competency with Code
Draw an orbital diagram to represent the electronic configuration of atoms
(STEM_GC11ESIIa-b-58)
Support Competencies:
1. Identify the total number of electrons of an element.
2. Identifty the number of unpaired electron in an atom.
3. Draw the orbital diagram of the elements.
II. Background Information for Learners
Orbital diagrams are pictorial descriptions of the electrons in an atom. Three
rules are useful in forming orbital diagrams. These are the Aufbau Principle, Pauli’s
Exclusion Principle and Hunds Rule. According to the Aufbau Principle, each electron
occupies the lowest energy orbital. The Pauli Exclusion Principle says that only two
electrons can fit into a single orbital. While Hund’s rule states that each orbital is filled
with one electron with parallel spins before any of them is filled with the opposite spin
electrons.
In this learning activity, you will learn more about how to draw the orbital diagram
of an element and identify the number of paired and unpaired electrons. You will also
be able to identify how many electrons are present in each orbital and the spin of each
electron.
III. Activity Proper
Activity 1
Directions: Read and understand the following notes to guide you in answering
the succeeding activities.
In most natural circumstances, change proceeds toward the lowest possible
energy. High-energy systems are considered unstable. Unstable systems lose
energy to become more stable. In the atom, electrons and the nucleus interact to
make the most stable arrangement possible. The ways in which electrons are
arranged around the nuclei of atoms are called electron configurations.

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The location of the electrons in an atom can be predicted by applying three
important rules: Aufbau Principle, Pauli’s Exclusion Principle, and Hund’s Rule.
1. Aufbau Principle.
• Electrons enter orbitals of lowest energy first.
• Electrons are added one at a time to the lowest energy orbitals available until
all the electrons of the atom have been accounted for.
• The last electron that enters an orbital is called the differentiating electron.
• It makes the configuration of an atom different from that of the other atom.
1
• Below is the order in which atomic sublevels are filled in an atom.
• Starting with the 1s orbital and move downward, following the direction of the
arrows, the order goes as follows: 1s<2s<2p<3s<3p<4s<3d<….<.
• Recall that the maximum number of electron capacity for the s is 2, p is 6, d is
10 and f is 14 and then rewriting the ground state electron configuration in
standard form, you have:
1s2
2s2
2p6
3s2
3p6
4s2
3d10
4p6
5s2
4d10
5p6
6s2
4f14
5d10
6p6
7s2
……
• For example the electron configuration of 20Ca is 1s2 2s2 2p6 3s2 3p64s2
2. Pauli’s Exclusion Principle.
• States that only two electrons can occupy the same orbital and two electrons
must spin in opposite directions.
• When electrons with opposite spin occupy an orbital, the electrons are said to
be paired.
• A single electron present in an orbital is said to be unpaired.
• For example, the electron configuration of Boron atom is 1s2
2s2
3s1
.
• The 1s and 2s orbitals can hold a maximum of two electrons.
• The fifth electron goes into the next energy level, the 3s.
• Boron atom contains 2 paired electrons and 1 unpaired electron
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
5s 5p 5d 5f
6s 6p 6d
7s 7p

7. 3
3. Hund’s Rule.
• When orbitals are of about the same energy, each orbital is filled with one
electron with parallel spins before any of them is filled with the opposite spin
electrons.
• For example, five electrons would occupy the p orbital of equal energy.
• The 3 electrons singly occupy first the orbital with aligned spin as
• The remaining 2 electrons must go into two of the p orbital as
Example:
Electron Configurations of Selected Elements
Element
Total
Electrons
Orbital Diagram Electron Configuration
(Standard Form)
1s 2s 2p 3s 3p
H 1 1s1
He 2 1s2
N 7 1s2
2s2
2p3
O 8 1s2
2s2
2p4
Ne 10 1s2
2s2
2p6
Na 11 1s2
2s2
2p6
3s1
Si 14 1s2
2s2
2p6
3s2
3p2
Cl 17 1s2
2s2
2p6
3s2
3p5

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Directions: Complete the table below by giving the atomic number, orbital diagram and
the electron configuration of the following given elements. Write your answers on your
answer sheet.
Element
Total
Electrons
Orbital Diagram Electron
Configuration
(Standard Form)
1s 2s 2p 3s 3p
He
Li
C
F
B
Mg
P
Ar
Activity 2
Another method to represent electron configuration is by using the abbreviated
electron configuration or the core method. The noble gas immediately before the
given atom is used as the “core” atom. For example, [Kr] is used as the core for atom
with atomic numbers 37-53. [Ar] stands for the electron configurations of argon and
it indicates the filling of all sublevels through 4p6.
The outer sublevels are rearranged so that the sublevels of the highest principal
level are the outermost. The outer electrons are the one responsible for the chemical
behavior of the element. For example, we can write the electron configuration of
Bromine atom as [Ar] 4s2
4p5
.
Electron configurations of a few elements do not conform to the Aufbau
principle. These exceptions do not have any major chemical consequences although
they are interesting to know. The exceptions occur in the chromium and copper
families. Using the Aufbau principle, you would expect the following electron
configurations for Cr and Cu:
Cr 1s2
2s2
2p6
3s2
3p6
4s2
3d4
Cu 1s2
2s2
2p6
3s2
3p6
4s2
3d9
But determined experimentally, the actual configurations are
Cr 1s2
2s2
2p6
3s2
3p6
4s1
3d5
Cu 1s2
2s2
2p6
3s2
3p6
4s1
3d10
These arrangements give chromium a half-filled d sublevel and copper a filled
d sublevel. Filled energy sublevels are more stable than partially filled sublevels. Half-
filled levels are not as stable as filled levels, but they are more stable than other

9. 5
configurations. Therefore, chromium and copper atoms are more stable with only one
electron in the 4s sublevel.
Example:
Write the abbreviated electron configurations and determine the number of unpaired
electrons of the following elements: F, Nb, and Es
Atom
Electron
Configuration
(Abbreviated Form)
Orbital Diagram
No. of
Unpaired
Electrons
F [He] 2s2
2p5
[He] 1
Nb [Kr] 5s2
4d3
[Kr] 3
Es [Rn] 7s2
5f11
[Rn] 3
Directions: Complete the table by filling in the abbreviated electron configurations and
determine the number of unpaired electrons of the following given elements. Write you
answers on your answer sheet.
Atom Electron
Configuration
(Abbreviated Form)
Orbital Diagram
No. of
Unpaired
Electrons
Cs
Ge
Sb
Ho
Bk
Reflection
Complete the statements below.
I understand_________________________________________________________
___________________________________________________________________
I don’t understand ___________________________________________________
___________________________________________________________________
I need more information about ___________________________________________
___________________________________________________________________
2s
5s
7s
2p
4d
5f

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VI. Answer Key
Activity
1
Element
Total
Electrons
Orbital
Diagram
Electon
Configuration
(Standard
From)
1s
2s
2p
3s
3p
He
2
1s
2
Li
3
1s
2
2s
1
C
6
1s
2
2s
2
2p
2
F
9
1s
2
2s
2
2p
5
B
5
1s
2
2s
2
2p
1
Mg
12
1s
2
2s
2
2p
6
3s
2
P
15
1s
2
2s
2
2p
6
3s
2
3p
3
Ar
18
1s
2
2s
2
2p
6
3s
2
3p
6

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VII. Links/ Other References:
Google. (Orbita Diagram). Accessed November 14, 2020
https://www.brightstorm.com/science/chemistry/the-atom/orbital-
diagrams/#:~:text=Orbital%20diagrams%20are%20pictorial%20descriptions,fit%20int
o%20an%20single%20orbital.
Google. (Chemistry). Accessed November 14, 2020
https://chem.libretexts.org/Under_Construction/Purgatory/Essential_Chemistry_(Curri
ki)/Unit_1%3A_Atomic_and_Molecular_Structure/1.4%3A_Electron_Configuration_a
nd_Orbital_Diagrams
Activity
2
Atom
Electron
Configuration
(Abbreviated
Form)
Orbital
Diagram
No.
of
Unpaired
Electron
6s
0
Cs
[Xe]
6s
2
[Xe]
4s
3d
4p
Ge
[Ar]
4s
2
3d
10
4p
2
[Ar]
2
5s
4d
5p
Sb
[Kr]
5s
2
4d
10
5p
3
[Kr]
3
6s
4f
Ho
[Xe]
6s
2
4f
11
[Xe]
3
7s
5f
Bk
[Rn]
7s
2
5f
9
[Rn]
5