CHEM 1: GENERAL CHEMISTRY (ORGANIC CHEMISTRY)
College of Liberal Arts, Sciences and Education
Prepared by: Donh Arturo M. Tabernilla
Jolina S. Arellano
MODULE 2
NATURE AND STRUCTURE OF ATOMS
Brief Introduction or Description
In this module students will recall and learn about the nature and structure of atoms. This
will include the structure of atoms, its electronic configuration, and the shape of atom’s orbitals.
Learning Outcomes:
By the end of the module, you should be able to:
1.
2.
3.
4.
Describe the structure of atoms.
Write electronic configuration of atoms.
Understand the shape of atomic orbitals.
Draw chemical structures of atoms
Pre-Activity - Before Reading Questions
1. How atoms do looks like?
2. What Are Atoms Made Of?
3. Draw the structure of an atom with label of its parts.
Lesson 2
INTRODUCTION
Atoms are the smallest particles of an element that retain the chemical properties of the
element; the interaction among atoms accounts for the properties of matter.
I. Atomic Structure
In 1808, the English chemist John Dalton put forth a model of matter that underlies modern
scientific atomic theory. The major difference between Dalton’s theory and that Democritus is that
Dalton based his theory on evidence rather than on a belief. First, let us state his theory. We will then
see what kind of evidence supported it.
1. All matter is made up of very tiny, indivisible particles, which Dalton called atoms.
2. All atoms of a given element have the same chemical properties. Conversely, atoms of differentelements have different chemical properties.
3. In ordinary chemical reactions, no atom of any element disappears or is changed into an atom of
another element.
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CHEM 1: GENERAL CHEMISTRY (ORGANIC CHEMISTRY)
College of Liberal Arts, Sciences and Education
Prepared by: Donh Arturo M. Tabernilla
Jolina S. Arellano
4. Compounds are formed by the chemical combination of two or more different kinds of atoms. In
a given compound, the relative numbers of atoms of each kind of element are constant and are
most commonly expressed as integers.
5. A molecule is a tightly bound combination of two or more atoms that acts as a single unit.
Figure 1. Atomic Structure
https://byjus.com/jee/atomic-structure/
Three Subatomic Particles
Today, we know that matter is more complex than Dalton believed. A wealth of
experimental evidence obtained over the last 100 years or so has convinced us that atoms are
not indivisible, but rather, consist of even smaller particles called subatomic particles. Three
subatomic particles make up all atoms: protons, electrons, and neutrons. There are many other
subatomic particles, but we will not deal with them in this lesson.
1. A proton has a positive charge. By convention we say that the magnitude of the charge is
+1. Thus, one proton has a charge of +1, two protons have a charge of +2, and so forth.
The mass of a proton is 1.6726 X 10-24 g, but this number is so small that it is more
convenient to use another unit, called the atomic mass unit (amu), to describe its mass.
1 amu = 1.6605 x 10-24 g Thus, a proton has a mass of 1.0073 amu. For most purposes
in this book, it is sufficient to round this number to one significant figure, and therefore,
we say that the mass of a proton is 1 amu.
2. An electron has a charge of —1, equal in magnitude to the charge on a proton, but
opposite in sign. The mass of an electron is approximately 5.4858 x 10r4 amu or 1/1837
that of the proton. It takes approximately 1837 electrons to equal the mass of one
proton. Like charges repel, and unlike
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CHEM 1: GENERAL CHEMISTRY (ORGANIC CHEMISTRY)
College of Liberal Arts, Sciences and Education
Prepared by: Donh Arturo M. Tabernilla
Jolina S. Arellano
charges attract. Two protons repel each other, just as two electrons also repel each
other. A proton and an electron, however, attract each other.
3. A neutron has no charge. Therefore, neutrons neither attract nor repel each other or any
other particle. The mass of a neutron is slightly greater than that of a proton: 1.6749 X
10-24 g or 1.0087 amu. Again, for our pur-poses, we round this number to 1 amu.
These three particles make up atoms, but where are they found? Protons and neutrons are
found in a tight cluster in the center of an atom which is called the nucleus. Electrons are found as a
diffuse cloud outside the nucleus.
Atomic Mass Number
Each atom has a fixed number of protons, electrons, and neutrons. One way to describe an
atom is by its mass number (A), which is the sum of the number of protons and neutrons in its nucleus.
Note that an atom also contains electrons, but because the mass of an electron is so small compared to
that of protons and neutrons electrons are not counted in determining mass number.
Mass number (A) = the number of protons + neutrons 1th in the nucleus of an atom PO/ For
example, an atom with 5 protons, 5 electrons, and 6 neutrons has a mass number of 11.
Atomic Number
Atomic number (Z) = number of protons in the nucleus of an atom Note that in a neutral atom,
the number of electrons is equal to the number of protons. Atomic numbers for all the known elements
are given in the atomic weight table on the inside front cover. They are also given in the Periodic Table
on the inside front cover. At the present time, 118 elements are known. These elements have atomic
numbers from 1 to 118. The smallest atomic number belongs to the element v which has only one
proton and the largest (so far), to the as -yet-unn amed heaviest known element, which contains 118
protons. If you know the atomic number and the mass number of an element, you can properly identify
it. For example, the element with 6 protons, 6 elec-trons, and 6 neutrons has an atomic number of 6 and
a mass number of 12. The element with atomic number 6 is carbon, C. Because its mass number is 12, we
call this atomic nucleus carbon- 12. Alternatively, we can write the symbol for this atomic nucleus as 1C. In
this symbol, the mass number of the element is always written in the upper-left corner (as a superscript)
of the symbol of the element and the atomic number in the lower-lefttctobronoekr (as a subscript). See
the two tables on the inside front cover of the ex for more information. Mass number (number of
protons 4- neutrons) '12c Atomic number is number of proton.
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CHEM 1: GENERAL CHEMISTRY (ORGANIC CHEMISTRY)
College of Liberal Arts, Sciences and Education
Prepared by: Donh Arturo M. Tabernilla
Jolina S. Arellano
Electron Shells
Electrons within an atom are grouped into main energy levels called electron shells. An electron
shell is a region of space about a nucleus that contains electrons that have approximately the same
energy and that spend most of their time approximately the same distance from the nucleus.
Electrons that occupy the first electron shell are closer to the nucleus and have a lower energy
than electrons in the second electron shell. Electron shells are numbered 1, 2, 3, and so on, outward
from the nucleus. Electron energy increases as the distance of the electron shell from the nucleus
increases. An electron in shell 1 has the minimum amount of energy that an electron can have. The
maximum number of electrons that an electron shell can accommodate varies; the higher the shell
number (n), the more electrons that can be present. In higher-energy shells, the electrons are farther
from the nucleus, and a greater volume of space is available for them; hence more electrons can be
accommodated. (Conceptually, electron shells may be considered to be nested one inside another,
somewhat like the layers of flavors inside a jawbreaker or similar type of candy.) The lowest-energy shell
(n = 1) accommodates a maximum of 2 electrons. In the second, third, and fourth shells, 8, 18, and 32
electrons, respectively, are allowed. The relationship among these numbers is given by the formula 2n',
where n is the shell number. For example, when n = 4, the quantity 2n2 = 2(4)2 = 32.
Electron Subshells
Within each electron shell, electrons are further grouped into energy sublevels called electron
subshells. An electron subshell is a region of space within an electron shell that contains electrons that
have the same energy. We can draw an analogy between the relationship of shells and subshells and the
physical layout of a high-rise apartment complex. The shells are analogous to the floors of the
apartment and the subshells are the counterparts of the various apartments on each floor.
The number of subshells within a shell is the same as the shell number. Shell 1 subshell contain
a subshell, shell 2 contains two subshells, and shell 3 contains three subshells, and so on.
Subshells within a shell differ in size (that is, the maximum number of electrons, they can
accommodate) and energy. The higher the energy of the contained electrons, the larger the subshell.
Subshell size (type) is designated using the letters s, p, d, and f. Listed in this order, these letters
denote subshells of increasing energy and size. The lowest-energy subshell within a shell is always the s
subshell,
the
next
highest
is
the
p
subshell,
then
the
d
subshell,
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CHEM 1: GENERAL CHEMISTRY (ORGANIC CHEMISTRY)
College of Liberal Arts, Sciences and Education
Prepared by: Donh Arturo M. Tabernilla
Jolina S. Arellano
and finally the f subshell. An s subshell can accommodate 2 electrons, a p subshell 6 electrons, a d subshell
10 electrons, and an f subshell 14 electrons.
II. Electron Orbitals
Electron subshells have within them a certain, definite number of locations (regions of space),
called electron orbitals, where electrons may be found. In our apartment complex analogy, if shells are
the counterparts of floor levels and subshells are the apartments, then electron orbitals are the rooms
of the apartments. An electron orbital is a region of space within an electron subshell where an electron
with a specific energy is most likely to be found.
Shell
1
2
3
4
s
1
2
3
1
Orbitals
p d f
3
3
3
5
5
7
Total Electrons Possible
2
8
18
32
•
Energy level 1 contains up to two electrons in a spherical orbital called a 1s orbital
•
Energy level 2 contains up to eight electrons; two in a 2s-orbital and two in each of three
orbitals designated as 2p-orbitals. The p-orbitals have a barbell type shape and are aligned along
x, y, and z axes. They are thus called the px, py and pz orbitals.
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CHEM 1: GENERAL CHEMISTRY (ORGANIC CHEMISTRY)
College of Liberal Arts, Sciences and Education
Prepared by: Donh Arturo M. Tabernilla
Jolina S. Arellano
•
Energy level 3 contains up to eighteen electrons, two electrons in a 3s orbital, six electrons in
the three 3p orbitals, and ten electrons in the five 3d orbitals.
•
Energy level 4 contains up to thirty-two electrons, two electrons in a 4s-orbitals and fourteen
electrons in the seven 4f-orbitals.
III. Writing Electron Configurations and Orbital Diagrams
An electron configuration is a statement of how many electrons an atom has in each of its
electron subshells. Because subshells group electrons according to energy, electron configurations
indicate how many electrons of various energies an atom has.
Electron configurations are not written out in words; rather, a shorthand system with symbols is used.
Subshells containing electrons, listed in order of increasing energy, are designated by using number—
letter combinations (Is, 2s, and 2p). A superscript following each subshell designation indicates the
number of electrons in that subshell. The electron configuration for nitrogen in this shorthand notation is
1𝒔𝟐2𝒔𝟐2𝒑𝟑
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CHEM 1: GENERAL CHEMISTRY (ORGANIC CHEMISTRY)
College of Liberal Arts, Sciences and Education
Prepared by: Donh Arturo M. Tabernilla
Jolina S. Arellano
Activity - After Reading Questions/Discussion Questions:
1. What do you think the importance of knowing the structure of atoms before moving on to
the next lesson which is about chemical bonding?
2. Give the electron configuration of the first 10 elements in the periodic table.
Reflection
Discussion of reflection from the activity will be done in class/synchronous session.
References:
Empire, R. (2013). The Science Of Alchemy | Future5 Summary. 3–4. Periodic
Table of the Elements. (2000). Physical Chemistry, xvii.
https://doi.org/10.1016/b978-012508345-4/50002-2
Quining, N. and Sacramento, J.J. (2016). General Chemistry, Vibal Group Inc., Araneta Avenue, Quezon
City
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