SHS

General Chemistry 1
Quarter 2 – Week 4
Module 4 - Lewis Structure of Molecular Covalent
Compounds
General Chemistry 1
Grade 11/12 Quarter 2 - Module 4- Lewis Structure of Molecular Covalent
Compounds
First Edition, 2020

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La Union Schools Division
Region I

All rights reserved. No part of this module may be reproduced in any form
without written permission from the copyright owners.

Development Team of the Module

Author: ELVIRA A. DELMENDO, MT-II

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 General Chemistry 1
Quarter 2 – Week 4
Module 4 - Lewis Structure of
Molecular Covalent Compounds
 Target

The Lewis structure of a molecule shows how the valence electrons are
arranged among the atoms in the molecule. These representations are named after
Gilbert Newton Lewis. In writing Lewis structures, the rule is that only the valence
electrons are included, using dots to represent electrons. The general concept is that
atoms make use of their valence electrons in chemical bonding. Since, the outermost
electrons are the ones that are highest in energy and farthest from the nucleus and
are therefore the ones that are most exposed to other atoms when bonds form.
Covalent bond is the result of the sharing of electrons between two atoms
which can be achieved in two ways: First is, the sharing of electrons between atoms
of the same kind (examples: of H2, Cl2, O2, etc.). Second, the sharing of electrons
between atoms of different kind (Examples: CH4, H2O, NH3, etc.). Covalent
compounds are composed of two or more different nonmetal atoms. It is represented
by electron-dot (circles or dots) or Lewis formulas. An electron pair (:) or a dash
between two atoms represents a covalent bond. When the two atoms share one pair
of electrons, as in H2, the bond is called a single bond, when two pairs are shared, as
in O2, it is called double bond. When they share three pairs, as in N2, it is called triple
bond.
In a molecule, there is a central atom (C) that holds all other atoms. The atoms
attached to it are called bonded atoms (B). Valence electrons of the central atom that
do not participate in molecule formation are called lone pairs (L). Lone pairs of
electrons affect the geometry of molecules. Many physical and chemical properties
such as boiling points and density of molecules are affected by the way atoms are
arranged. The arrangement of atoms in a molecule is called the geometry of
molecules.
This Learning Material will provide you simple problem-solving strategy,
activities and simple exercises on drawing the Lewis structure of some covalent
compounds then, the geometry of the simple compounds will be described.
After going through this Learning Material, you are expected to:

• Draw Lewis structure of molecular covalent compounds (STEM_GC11CBIId-

g-78)
• Describe the geometry of simple compounds (STEM_GC11CBIId-g-81
- To use the VSEPR model to predict molecular geometries.

Ahhaaa!!! Before you proceed to the lesson proper, you need to find out how much you know
about the topic and you will be guided on what to be focused on. Take it easy! Good luck!!!
PRE-TEST
A. Directions: Match the covalent compounds below by choosing the
correct Lewis structure in the box. Write your answer on a separate
sheet by writing the LETTER only.
1. Carbon Tetrachloride (CCl4)
2. Ammonia (NH3)
3. Phosphorus trichloride (PCl3)
4. Water (H2O)
5. Methane (CH4)
CHOICES
A. B. C.

D. E. F.

G. H. I.

B. Directions: Read the questions very well and choose the LETTER of the
correct answer. Use a separate sheet to write your answers.
6. Which of the following choices is represented by a covalent bond electron/s?
A. A single shared C. A pair of transferred
B. A pair of shared D. A pair of unshared
7. How many covalent bonds can oxygen form?
A. Two B. Three C. Four D. Six
8. How do you describe the shape of carbon dioxide?
A. Linear B. Octahedral C. Tetrahedral D. Trigonal Planar
9. What shape is formed when there are four (4) electron pairs in a certain
covalent compound?
A. Linear B. Planar C. Tetrahedral D. Trigonal
10. What shape is formed by a chemical compound with1200 bond angle having 3
electron pairs?
A. Linear B. Octahedral C. Tetrahedral D. Trigonal Planar
 11. What is the bond angle of a linear structure of a covalent compound?
A. 900 B. 109.50 C. 1200 D. 1800
(For numbers 12-15). How will you describe the geometrical shape formed by the
given Lewis structures of compounds below?

Select your answer from these choices:

A. Bent B. Linear C. Tetrahedral D. Trigonal Pyramidal

12.

13.

14.

15.

Just enjoy and take enough time in answering the activities in this module. Don’t worry if you
cannot give the correct answer yet in the Pre-test. It will serve you as a guide on what to focus
and study on in this module.
 Jumpstart

Individual molecules cannot be easily studied. The mass of an atom in a

molecule does not change nor the identities of the individual atoms. An oxygen
atom in water is the same oxygen atom in sugar, or in any number of other
compounds.

Discover

GUIDE IN WRITING THE LEWIS STRUCTURES OF SOME COVALENT

COMPOUNDS
Let us consider the following steps:
1. Determine the total valence electrons of the atoms in the molecule.
Before we give the total valence electrons, let us review how valence
electrons are determined in each element.
Example element: Oxygen, O2
• Use the periodic table of elements to find out the atomic number of the
elements. In the given example, the atomic number of Oxygen is 8.
• Next is to do the electronic configuration:
8O – 1s2 2s2 2p4 , to illustrate this using the Bohr Model would look like
this:
Note: Valence electron is
2 6 valence electron the electron found at the
outermost energy level or
known as the valence
shell.
Now that you know how to get the valence electron, you are ready to draw the
Lewis-Dot structure of the element, it looks like this:

How many dots are there?

If your answer is 6, that

number represents the
number of valence electron.

What about for molecules? Polyatomic anions and for polyatomic

cations? How will you determine their valence electrons?
Note:
For molecules – sum all valence electrons for all the atoms
For polyatomic anions - add the number of negative charges
For polyatomic cations - subtract the number of positive charges

For example:

CO2
(4x1) (6x2) The sum is: 4+12 = 16 valence electrons

Try this: NH4 - What is the total number of valence electrons?

2. Choose the central atom, it is usually the least electronegative element in the
compound and it is usually the first atom in the molecular formula or the atom
with higher covalency. Write the sequential arrangement of the atoms in a
molecule, (the so called skeleton). Chemists usually list this central atom first in
the chemical formula (as in CCl4 and CO32−, which both have C as the central
atom), which is another clue to the compound’s structure. Hydrogen and the
halogens are almost always connected to only one other atom, so they are
usually terminal rather than central.

Example:

NH3 Note: N is the central atom

H N H

H
3. Draw dots around the atoms and in between the elements or atoms in the
skeleton formula to distribute the electrons.
Note: A dash ( ) is used to connect two dots which represents the covalent
bond between two atoms. The dots are arranged to satisfy the OCTET RULE (with
eight valence electrons in each atom/element), but hydrogen has two only.
Example: H2 H H

Note: The valence electron of hydrogen is

and o, it looks this way: one, so it needs another one atom of H to
share the valence electron and to become
H H stable. Thereby, it satisfies the octet rule.
Connect the two dots to form a single bond.

4. If there are not enough electrons to give eight electrons to each atom (except
hydrogen), shift unbonded electrons as necessary, or change single bonds to
double or triple bonds.
5. Finally, count the electrons to verify the total number of electrons distributed
around each atom to satisfy the duet rule for hydrogen and octet rule for the
second-row elements but there are exceptions to the rule.

You are great! Now, that you are familiar on how to draw the Lewis structure of
the covalent compounds, let us connect the lesson to another topic which is to
describe the geometrical shapes of some simple compounds. Get ready and enjoy
the next activity!

How do we predict the shapes of the molecules?

The shape of molecules can be predicted by the combination of the Lewis theory
and VSEPR theory. VSEPR (pronounce as vesper) model means valence shell
electron-pair repulsion model. It is formed from molecules of nonmetals.
STEPS IN APPLYING VSEPR MODEL
1. Draw the Lewis structure for the molecule.
Example: BeCl2, Beryllium chloride
Find the valence electron of Be, Beryllium and Cl, Chlorine

4Be – 1s2 2s2 valence electron = 2

17Cl – 1s2 2s2 2p6 3s2 3p5 valence electron = 2+5= 7

What is the central atom (A)?

A or the central atom is Be Be

X or the terminal atom is Cl Cl

 Now, combine the two elements to become compound.

Cl Be

Note: A line represents bonding electrons, but what do you observe with the electron of
Beryllium? Is there a missing piece? Yes, there is a need to add another chlorine to share its
electron and become stable.

So, it becomes like this:

Cl Be Cl

2. Count the electron pairs and arrange them to minimize repulsion by putting
the pairs as far apart as possible.
3. Determine the positions of the atoms from the way the electron pairs are shared.
4. Name the molecular structure from the positions of the atoms.
Let us study Table 1 of the electron pair repulsion model to predict the shape of
some covalent compounds.

The table below gives the common molecular shapes. In this table we use A to
represent the central atom, X to represent the terminal atoms (i.e. the atoms
around the central atom) and E to represent any lone pairs
TABLE 1. Common Molecular Shapes

Number of Number of Geometry General Bond Angle

bonding lone pairs Formula (degrees)
electron pairs
1 or 2 0 Linear AX or AX2 180
2 2 Bent or angular AX2E2 109.5
3 0 Trigonal planar AX3 120
3 1 Trigonal AX3E 109.5
pyramidal
4 0 Tetrahedral AX4 109.5
5 0 Trigonal AX5 90, 120
bipyramidal
6 0 Octahedral AX6 90
Source: https://intl.siyavula.com/read/science/grade-11/atomic-
combinations/03-atomic-combinations-02#fig:shapes
Additional information:

✓ The term electron-pair geometry is the name of the geometry of the electron-
pair/groups/domains on the central atom, whether they are bonding or non-
bonding. It provides a guide to the bond angles of between a terminal-central-
terminal atom in a compound. Molecular geometry is the name of the
 geometry used to describe the shape of a molecule. So, when asked to describe
the shape of a molecule we must respond with a molecular geometry. If asked
for the electron-pair geometry on the central atom we must respond with the
electron-pair geometry. To determine the shape (molecular geometry) of a
molecule you must write the Lewis structure and determine the number of
bonding groups of electrons and the number of non-bonding pairs of electrons
on the central atom, then use the associated name for that shape.

Guide Questions:
1. In the example given above (BeCl2, Beryllium chloride) what do you think is
the number of bonding electron pairs? If your answer is two, you are correct!
2. Is there a lone pair? The correct answer must be, there is no lone pair.
3. Can you give the general formula formed? The answer is AX 2.
4. Can you describe the geometric shape of BeCl2, based from your answers on
the given questions above? Very good! The answer is linear.

Note: To familiarize yourself on the different geometric shapes, study the figures below.

FIGURE 1. The common molecular shapes.

Source:https://intl.siyavula.com/read/science/grade-11/atomic-combinations/03-
atomic-combinations-02
 FIGURE 2. The common molecular shapes in 3-D.

Source:https://intl.siyavula.com/read/science/grade-11/atomiccombinations/03-atomic-
combinations-02

YOU ARE DOING WELL! Just continue with the activities on the next part of this
Learning Material! Come on!
 Explore

ACTIVITY 1: IT’S DRAWING TIME!

Directions: Complete the table below by drawing the Lewis structure of the given
atoms and compounds.

Covalent Central Atom Terminal Atom Lewis structure of the

Compound compound

BeCl2 Be Cl Cl B C

PCl5

BF3

NH3

CH4

SF6
 Deepen

ACTIVITY 2: The Illusion!

Directions: Complete the table below to describe the shape of the molecular
compounds. You may refer to the table shown above.

Covalent Bonding Nonbonding General Shape

Compound Formula
Example:
BeCl2 2 0 AX2 linear
H2O

BF3

NH3

CH4

SF6

Note: The bonding electrons are the shared electron pair while the nonbonding
electrons are the lone pairs (electrons not involved in the formation of bonds). In the
example, Be is the central atom surrounded by two bonding electrons and with no
lone pairs. So, the general formula is AX 2. In order to describe the shape, you may
use table 1 to guide you in describing the shape of the molecular compounds.

CONGRATULATIONS for doing the activities well!!! Let’s check how much you
gained from the different activities you’ve done by answering the questions on the
next page. Goodluck and give your best!
 Gauge

Directions: Read the questions properly with understanding. Answer the

questions correctly by writing the LETTER on the prepared answer sheet.
1. A covalent molecule has three bonding electron pairs and one lone pair.
The molecule has a general formula of AX3E. Which of the following choices is
the correct shape of the molecule?
A. Linear B. Planar C. Tetrahedral D. Trigonal Pyramidal

2. How do you describe the shape of methane, CH 4?

A. Octahedral B. Planar C. Tetrahedral D. Trigonal Pyramidal

3. How do you describe the shape of the molecule that looks like the figure below?

A. Bent B. Octahedral C. Tetrahedral D. Trigonal planar

4. Which of the following choices is represented by a covalent bond electron/s?

A. A single shared C. A pair of transferred
B. A pair of shared D. A pair of unshared

5. How many covalent bonds can carbon form?

A. Two B. Three C. Four D. Six

6. How do you describe the shape of methane, CH4?

A. Linear B. Octahedral C. Tetrahedral D. Trigonal Planar

7. What shape is formed when there are two (2) electron pairs in a certain
covalent compound?
A. Linear B. Planar C. Tetrahedral D. Trigonal

8. What shape is formed by a chemical compound with109.50 bond angle having

2 electron pairs and 2 lone pairs?
A. Bent B. Octahedral C. Tetrahedral D. Trigonal Planar
 9. What is the bond angle of an octahedral structure of a covalent compound?
A. 900 B. 109.50 C. 1200 D. 1800

10. Your teacher asked you to draw the Lewis structure of a trigonal planar
molecule, which of the following should have been drawn?

A. B. C. D.

11. Which of the following geometric shapes has one lone pair of electrons?
A. Octahedral B. Tetrahedral C. Trigonal Planar D. Trigonal Pyramidal

12. Which one CORRECTLY shows trigonal planar?

A. B. C. D.

13. Which of the figures in number 12 choices shows the molecular structure of
water, H2O?
14. Which one in number 12 choices has an angle of 120 0?
15. How will you draw the Lewis model of a molecule with a general formula of
AB3E? Select your answer from number 12 choices.

Wow!!! CONGRATULATIONS for giving your best and for accomplishing the
Learning Materials enjoyably!
 EXPLORE: ACTIVITY 1
1. F 6. B 11. D
2. B 7. A 12. C
3. C 8. A 13. D
4. G 9. C 14. A
5. A 10. D 15. B
Pre-Test
KEY ANSWER
1. A 6. C 11. D
2. C 7. A 12. B
3. D 8. A 13. A
4. B 9. A 14. B
5. C 10. B 15. C
Gauge
DEEPEN: ACTIVITY 2
REFERENCES:
Printed Materials:
Ilao, Luciana V., et.al. General Chemistry 1.Rex Bookstore, Inc. (Sta. Mesa Heights
Quezon City: SD Publications, Inc., 2001), 194-219.
Brown, Theodore L. Chemistry the Cental Science. (Person Education Asia. Pte.
Ltd, 2002), 278-314.
Caiquet, Rolando I., et.al. Chemistry III. St. agustine Publications, Inc. (1624-1626
Espaňa cor. Don Quijote St., Sampaloc, Manila) pp. 120-125.

Dorin, Henry (1982). Chemistry the Study of Matter. (Newton, Massachusetts.

CEBCO, A Division of Allyn and Bacon, Inc., 1982), 202.
Espaňa, Rebecca N., et. al. Abiva Publishing House, Inc. Abiva Bldg., 851-881 G.
Araneta Ave., Quezon City.pp. 110-119.
Mapa, Amelia P. et. al. Chemistry Textbook Science and Technology. (Sta. Mesa
Heights Quezon City: SD Publications, Inc., 2001), 120-131.
Zumdhal, Steven S. Chemistry An atoms First approach.2012 brooks/Cole,
Cengage Learning.pp. 169-201.
Website:
https://byjus.com/jee/covalent-bond/
https://byjus.com/chemistry/ammonia/
https://byjus.com/chemistry/methane/
https://socratic.org/questions/56ce891511ef6b034654fc53
https://2012books.lardbucket.org/books/principles-of-general-chemistry-
v1.0m/s13-molecular-geometry-and-covalen.html
https://www.angelo.edu/faculty/kboudrea/general/shapes/00_lewis.htm#Covalen
tBonds
https://intl.siyavula.com/read/science/grade-11/atomic-combinations/03-
atomic-combinations-02
http://intro.chem.okstate.edu/1314F00/Lecture/Chapter10/VSEPR.html
http://www.tutor-
homework.com/Chemistry_Help/Molecular_Geometry/006_Phosphorus_Pentachlor
ide_PCl5.html
https://geometryofmolecules.com/bf3-lewis-structure-hybridization-and-polarity/
http://www.tutor-
homework.com/Chemistry_Help/Molecular_Geometry/030_Ammonia_NH3.html
http://www.tutor-
homework.com/Chemistry_Help/Molecular_Geometry/027_Methane_CH4.html
https://www.google.com/search?q=sf6+structural+formula&rlz=1C1GCEA