MATERIAL STRUCTURE & INTERATOMIC BONDING

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MATERIAL STRUCTURE
&

INTERATOMIC BONDING

ROHANA BINTI SEMAAIL@ISMAIL
POILITEKNIK KOTA BHARU

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Jabatan Kejuruteraan Mekanikal
Politeknik Kota Bharu
KM. 24, Kok Lanas,
16450 Ketereh, Kelantan.

MATERIAL STRUCTURE & INTERATOMIC BONDING
First Edition 2022
© 2022 Rohana Binti Semaail@Ismail

All right reserved. No part of this publication may be reproduced, stored in a retrieval
system or transmitted in any form or by any means, electronics, mechanical,
photocopying, recording or otherwise without prior permission of the publisher.

MATERIAL STRUCTURE & INTERATOMIC BONDING/Rohana Binti

Semaail@Ismail

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APPRECIATION
Thanks to Allah swt for the strength that has been given to us in preparing this book. I would
also like to take the opportunity to express my gratitude to the Head of Mechanical
Engineering Department, Tuan Haji Zuhairy Bin Zahari for the trust given in carrying out
this task. A word of thanks also to Pn Ruzila Binti Mat Ghani, JKM's E-Learning
Coordinator, who jointly made revisions and edits, as well as comrades-in-arms who
contributed their thoughts and time directly and indirectly in strengthening the content of
this book. Not forgetting the family who have given a lot of support to make this ebook a
success.
MATERIAL STRUCTURE & INTERATOMIC BONDING/Rohana Binti

Semaail@Ismail

Jabatan Kejuruteraan Mekanikal
Politeknik Kota Bharu
KM 24 Kok Lanas
16450 Ketereh, Kelantan

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Material Structure & Interatomic Bonding

This book was written for topic 2, Material structure and atomic bonding for the subject
Material science and engineering. Subtopics discussed include introduction to atoms, electron
configuration, element, compound, mixture, periodic table of elements, atomic bonding and
crystal structure
The titles found in this book refer to the course curriculum DJJ 30113 Material Science and
Engineering, Polytechnic Malaysia. The content summary has been formulated by the lecturer
who teaches the subject DJJ 30113 and translated as scientific writing. Therefore, this book
is very suitable for students who are new to the field of Material Science.

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Author Biography

ROHANA BINTI SEMAAIL@ISMAIL was born on July 14, 1972 in small town called Bagan
Serai, Perak. She received early education at Sekolah Kebangsaan Matang Gerdu, Bagan Serai,
Perak and Sekolah Rendah Sri Labis, Labis, Johor. She was accepted as a student of Sekolah
Raja Perempuan Ta’ayah, Ipoh, Perak to continue her studies at secondary level. She holds
a Degree in Mechanical Engineering from Universiti Teknologi Malaysia after completed her
diploma in the same field. She currently works as a Lecturer of Mechanical Engineering
Department at Politeknik Kota Bharu, Kota Bharu, Kelantan. She had experienced in teaching
Material Science since 2012 and her teaching interest includes Material Science & Engineering
and Vehicle Dynamic.

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TABLE OF CONTENTS

Material Structure And Interatomic Bonding............................................................................... 9
Atom .................................................................................................................................................. 9
Nucleus of Atom ............................................................................................................................ 10
Proton .............................................................................................................................................. 10
Neutron............................................................................................................................................ 10
Electrons ......................................................................................................................................... 11
Atomic Number .............................................................................................................................. 11
Atomic mass................................................................................................................................... 12
Electrons configuration................................................................................................................. 13
Aufbau Principle............................................................................................................................ 15
Configuration using the Aufbau Principle .................................................................................. 16
Elements.......................................................................................................................................... 17
Compounds .................................................................................................................................... 19
Types of Compounds .................................................................................................................... 20
Mixture............................................................................................................................................ 23
Types Of Matter.............................................................................................................................. 24
Periodic Table Of Elements .......................................................................................................... 25
Periodic Table Of Elements Characteristics .............................................................................. 26
Usage Of Element Periodic Table............................................................................................... 27
Atomic Bonding ............................................................................................................................. 27
Ionic bond ....................................................................................................................................... 27
Covalent Bond ................................................................................................................................ 29

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Metallic Bond.................................................................................................................................. 30
Crystal Solid Structure.................................................................................................................. 32
Monocrystalline solid .................................................................................................................... 32
Polycrystalline solid....................................................................................................................... 33
Amorphous/Non-Crystalline Materials ....................................................................................... 34
Bravais Lattice................................................................................................................................ 35
Crystal Structure ............................................................................................................................ 36
BIBLIOGRAPHY................................................................................................................................41

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MATERIAL STRUCTURE AND INTERATOMIC
BONDING

T he existence of atoms has been proposed since the time of early Indian and Greek
philosophers (400BC) who were of the vies that atoms are the fundamental building
blocks of matter. The word ‘atom’ has been derived from the Greek word ‘a-tomio’ which
means ‘uncut-able’ or ‘non-divisible’. These ideas were mere speculations and there was no
way to test them experimentally and remained dormant for a very long time and were
revived again by scientists in the nineteenth century. In 1808 Dalton atomic theory had been
proposed by John Dalton, a British school teacher. The theory was able to explain the law of
conservation of mass, law of constant composition and law of multiple proportion very
successfully. However, it failed to explain the results of many experiments, for example, it
was known that substances like glass or ebonite when rubbed with silk or fur get electrically
charged. In this topic, we start with the result obtained by scientists towards the end of
nineteenth and beginning of twentieth century. These established that atoms are made of sub-
atomic particles, i.e., electrons, protons and neutrons.

Atom

Basically, atom is the smallest unit of matter in one unit. One atom consists primarily
of three basic subatomic particles which are, protons, neutrons and electrons. Protons and
neutrons are in the center of the atom, making up the nucleus. Electron surround the nucleus.
Figure 2.1: Illustrates nucleus, electron and orbits surrounding nucleus. Protons have a
positive charge. Electrons have a negative charge. The charge on the proton and electron are
exactly same size but opposite charge. Neutrons have no charge. Since opposite charges
attract, protons and electrons attract each other.

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Figure 2.1: Illustrates nucleus, electron and orbits surrounding nucleus

Nucleus of Atom

Nucleus is located at the center of atom. The diameter of nucleus is about 1/10000 of diameter
of whole atom. Almost whole mass of atom is concentrated in its nucleus. Nucleus itself
consists of two kinds of particles,

1. Proton
2. Neutron

Proton

Protons are positively charged particles. Charge on each proton is 1.6 × 10-19 Coulomb. The
number of protons in nucleus of an atom represents the atomic number of atoms.

Neutron

Neutrons do not have any electrical charge. Means, neutrons are electrically neutral particles.
The mass of each neutron is equal to mass of the proton.
The nucleus is positively charged due to the presence of positively charged protons. In any
material, the weight of the atom and radioactive properties are associated with the nucleus.

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Electrons

An electron is a negatively charged particle present in the atoms. Charge on each electron is
– 1.6 × 10 – 19 Coulomb. These electrons surround the nucleus. Some facts about electrons in
an atom are listed and explained below,

1. If an atom is having the same number of protons and electrons, the atom is electrically
neutral as the negative charge of electrons neutralizes the positive charge of protons.

2. The electrons revolve around the nucleus in shells (also called orbits).
3. A force of attraction is excreted on negatively charged electrons by positively charged

nucleus. This force of attraction works as centripetal force required for electrons
revolution around the nucleus.
4. The electrons which are near to nucleus are tightly bound with the nucleus and it is
more difficult to pull out (remove) these electrons from the atom than those which are
far away from the nucleus.

Each subatomic has its own charge and mass show in Table 2.1. The electron charge cloud
thus constitutes almost all the volume of the atom but accounts for only a very small part of
its mass. The electrons, particularly the outer ones, determine most the properties of the atom.
And thus a basic knowledge of atomic structure is important in the study of engineering
materials.

Table 2.1 The mass and charge of the proton, neutron and electron.

Sub-atom Mass(g) Charge (Coulombs)

Protons 1.673 x 10-24 + 1.602 x 10-9

Neutron 1.675 x 10-24 0

Electron 9.109 x 10-28 - 1.602 x 10-19

Atomic Number

The atomic number of atoms is the number of protons in the nucleus of an atom. The
number of protons define the identity of an element (i.e., in Figure 2.2: Shows an element with
6 protons is a carbon atom, and 13 protons is a aluminum atom, no matter how many neutrons
may be present). Atoms of an element that have the same atomic number but a different
number of neutrons are known as the isotopes of the element. Example, titanium (22Ti) is
composed of five stable isotope; 46Ti, 47Ti, 48Ti, 49Ti and 50Ti with 48Ti being the most abundant

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(73.8% natural abundance). The number 46, 47 and so on are the total numbers of protons and
neutrons. Because of atomic number of each element is fixed, the number of neutrons can be
calculated by subtracting protons number. For example, 46Ti consists 24 neutrons when 46
mines 22 is equal 24. Furthermore, the protons number is determines how many electrons
surround the nucleus, and it is the arrangement of these electrons that determines most of the
chemical behavior of an element.

Figure 2.2: Carbon and Aluminum atom

Atomic mass

Together, the number of protons and the number of neutrons determine an

element’s mass number: mass number = protons + neutrons. Mass number also called atomic

mass. A property closely related to an atom’s mass number is its atomic mass. The atomic
mass of a single atom is simply its total mass and is typically expressed in atomic mass units
or amu. By definition, an atom of carbon with six neutrons, carbon-12, has an atomic mass of
12 amu. In general, though, an atom's atomic mass will be very close to its mass number but
will have some deviation in the decimal places. Since an element’s isotopes have different
atomic masses, scientists may also determine the relative atomic mass or also called
the atomic weight for an element. The relative atomic mass is an average of the atomic masses

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of all the different isotopes in a sample, with each isotope's contribution to the average
determined by how big a fraction of the sample it makes up.

Electrons configuration

Each element in periodic table has different number of electrons. The electron
configuration is the standard notation used to describe the electronic structure of an atom
and to understand the shape and energy of its electrons. The electron configuration of an
atom also representation of the arrangement of electrons distributed among the orbital shells
and subshells. Commonly, the electron configuration is used to describe the orbitals of an
atom in its ground state, but it can also be used to represent an atom that has ionized into a
cation or anion by compensating with the loss of or gain of electrons in their subsequent
orbitals. Many of the physical and chemical properties of elements can be correlated to their
unique electron configurations. The valence electrons, electrons in the outermost shell, are
the determining factor for the unique chemistry of the element.
The arrangement of electrons in an atom can be determined by using simple formula as below:

e-max = 2n2 ; n = number of shell
Example 1. Lithium with atomic number is 3.

n = 1 ---------> 2(1)2 = 2 --------> 1st. shell carries 2 electrons.
Because the number of electrons is equal to the atomic number, which in Lithium is 3, the
remain 1 electron carried in 2nd shell or the outer shell. Figure 2.3: shows electrons configured
in Lithium. The number of electrons in the last orbit or outer shell is called electron valency.

Figure 2.3: Number of electrons in every shell Lithium atom

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Example 2: Potassium with atomic number is 19.
n = 1 ---------> 2(1)2 = 2 --------> 1st. shell carries 2 electrons.
n = 2 ---------> 2(2)2 = 8 --------> 2nd. shell carries 8 electrons.

Potassium atomic number is 19, first shell carries 2 electrons. Second shell carries 8 electrons.
There is 9 remain electrons. The 3rd. shell will carry 8 electrons and 1 last electron will carry
in the outer shell. Figure 2.4: shows electrons configured in Potassium.

Figure 2.4: Number of electrons in every shell Potassium atom
By using this formula, the number of electrons in every shell can be determined easily, shows
in Table 2.3. But this method actually identified as cannot satisfy to configure electrons in
each shell for every element on periodic table. Thus, Aufbau principle used.

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Table 2.2: Number of electrons in every shell.

Aufbau Principle

The word 'Aufbau' is German for 'building up'. The Aufbau Principle, also called the
building-up principle, states that electron's occupy orbitals in order of increasing energy. The
atom energy level increasing when the electrons getting farther from the nucleus. The order
of electrons occupation in each orbital is as follows:

1s<2s<2p<3s<3p<4s<3d<4p<5s<4d<5p<6s<4f<5d<6p<7s<5f<6d<7p
One way to remember this pattern, probably the easiest, is to refer to the periodic table and
remember where each orbital block falls to logically deduce this pattern. Another way is to
make a table like in the Figure 2.5 below and use vertical lines to determine which subshells
correspond with each other.

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Figure 2.5: Arrow shows the path to follow to calculate how many
electrons can be filled in each orbit.
The graphic shows arrow of the path to follow. Now that we know the order of orbitals to fill,
you need only memorize the size of each orbital.
S orbitals have one possible value of m to hold 2 electrons.
P orbitals have three possible value of m to hold 6 electrons.
D orbitals have five possible value of m to hold 10 electrons.
F orbitals have seven possible value of m to hold 14 electrons.
This is all you need to determine the electron configuration of a stable atom of an element.

Configuration using the Aufbau Principle

The notation seen on period tables for electron configurations uses the form:
nOe
n is the energy level
O is the orbital type (s, p, d, or f)
e is the number of electrons in that orbital shell.
Electron Configuration of Sulphur
The atomic number of Sulphur is 16, implying that it holds a total of 16 electrons. As per the
Aufbau principle, two of these electrons are present in the 1s subshell, eight of them are

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present in the 2s and 2p subshell, and the remaining are distributed into the 3s and 3p
subshells.
Therefore, the electron configuration of sulphur can be written as
1s2 2s2 2p6 3s2 3p4.
Electron Configuration of Nitrogen. The element nitrogen has 7 electrons (since its atomic
number is 7). The electrons are filled into the 1s, 2s, and 2p orbitals. The electron configuration
of nitrogen can be written as 1s2 2s2 2p3
Oxygen, O has eight protons and eight electrons. The Aufbau principle says the first
two electrons would fill the 1s orbital. The next two would fill the 2s orbital leaving the
remaining four electrons to take spots in the 2p orbital. This would be written as:
1s22s2 2p4
The Aufbau principle works for nearly every element tested. There are two exceptions to this
principle, Chromium and Copper.

Elements

An element is a substance that cannot be broken down into another substance. Each
element is made up of its own type of atom. The periodic table, shows in Figure 2.6, lists
elements in order of atomic number and is laid out so elements with similar chemical
properties form columns (groups). Element also could be defined as all materials or matters
that is composed of only ONE TYPE of ATOM

Table 2.3: Electron configuration using Aufbau Principal

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Example :
Relative metal such as gold and platinum, non-metal such as diamond, graphite and sulfer.
All of the elements have been named. Some of these names are familiar to us, such as carbon
and magnesium and some are less familiar, such as dysprosium and roentgenium. We can
also name elements using their atomic numbers. For example, element 1 is hydrogen, element
2 is helium, element 3 is lithium, element 8 is oxygen, etc.

Figure 2.6: Periodic table of elements

Compounds

A compound is a substance that results from a combination of two or more different chemical
elements, in such a way that the atoms of the different elements are held together by chemical
bonds that are difficult to break. These bonds form as a result of the sharing or exchange of
electrons among the atoms. The smallest unbreakable unit of a compound is called a molecule.

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4 scenarios occur when element expose or react to other elements or compounds. The
scenarios are:

1. Sometimes, when elements are mixed, the reaction occurs slowly. For example, when
iron is exposed to oxygen.

2. Sometimes, different elements can be mixed and no reaction occurs, so the elements
retain their individual identities.

3. Sometimes the reaction occurs rapidly such as when lithium is exposed to oxygen.
4. Sometimes, when an element is exposed to a compound, a reaction occurs in which

new compounds are formed. Example when pure elemental sodium is immersed in
liquid water.

Another fact about compound. Sometimes, when element react to others element, their states
are changed. For example, hydrogen (H) and oxygen (O). Both of elements are gases at room
temperature and normal atmospheric pressure. But when they combine into the familiar
compound known as water, each molecule of which contains two hydrogen atoms and one
oxygen atom (H 2 O), the resulting substance is a liquid at room temperature and normal
atmospheric pressure.

There is one group atoms of a few elements do not readily bond with other elements to form
compounds. These are called noble or inert gases: helium, neon, argon, krypton, xenon, and
radon. Certain elements readily combine with other elements to form compounds. Examples
are oxygen, chlorine, and fluorine.

Types of Compounds

Metallic compounds. A metallic compound is a compound that contains one or more metal
elements bonded to another element. Typically, the metal atom acts as the cation in the
compound and is bonded to a nonmetallic anion or an ionic group. Because it has a positive
charge, the metal element symbol is listed first in the chemical formula.

Most metals do not occur in their natural state. They are often found as compounds such as
metal oxides, sulfides and halides.

• Aluminum oxide is the main metal compound present in the ore known as bauxite.

• Iron pyrites or ‘fool’s gold’ is mainly iron sulfide.

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• The Lake Grass-mere salt works in Marlborough produces the metal compound
known as sodium chloride from ‘salty’ seawater.

Metals can be produced (smelted) from their ores by a variety of methods:
• Aluminum is produced from its ore (bauxite) by passing a very large
electric current through a molten mixture of the ore and a compound called cryolite.
• Titanium is mostly produced from its ore (rutile) by the Kroll Process, where the ore
is treated with chlorine gas followed by reaction with magnesium metal.

Table 2.4: Some examples of metallic compounds

Organic Compounds. Organic compounds belonging to the main class can be divided into
different families, known as homologous series, on the basis of similarity in structure and
chemical properties. All compounds having the same carbon framework (skeleton) and the
same functional group in their molecules possess similar properties. Such compounds when
arranged in order of their molecular masses constitute a series called homologous series and

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the individual members are called homologues. The property by virtue of which a number of
organic compounds form a homologous series is termed “homology”.
Table 2.5: Some examples of organic compounds

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Mixture

In chemistry a pure substance consists only of one element or one compound, but a mixture
consists of two or more different substances and not chemically joined together. Or it also can
be defined as combination of two or more constituents which joined without chemical
reaction. The components of a mixture can be separated without chemical reactions. For
example, shows in figure 2.7, there are many balloons of different colors tied together. The
balloons are then separated according to their color. Now several groups of balloons can be
seen with different colors.

Figure 2.6: Balloons separated according to different color
Hydrogen, H and Oxygen, O are both gases. Together, as a mixture, hydrogen and oxygen
can react and form water, H2O. Water is a compound of hydrogen and oxygen. There are
important differences between the properties of a mixture and a compound.
In Table 2.6, the column 'Mixture' refers to the gas hydrogen and oxygen, and the column
named 'Compound' refers to water.

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Table 2.6: Comparison between mixture and compound properties

Mixture Compound

Composition Variable composition - Constant composition - water
Joined or not? the relative amounts of always contains the same ratio
the two gases can be of hydrogen to oxygen. This
Properties changed. ratio is shown in the chemical
Separation formula of the compound -
The hydrogen and H2O.
oxygen are not joined
together. The hydrogen and oxygen
have joined together to form
Keeps the properties of the new substance water.
the substances
involved. This mixture Properties are different from
is in the gas state. those of the elements it
contains. This compound is a
The substances in the liquid.
mixture can be
separated. Cannot be separated but can
be obtained by using chemical
reactions.

Types Of Matter

In Periodic Table, there are 118 elements arranged according to its proton numbers. But most
materials encounter in the world are mixtures. The air is a mixture of oxygen, nitrogen and
other gases. The oceans are mixtures of water, salts and other substances.

Pure substance: A type of a matter with a fixed composition. Every sample has exactly the
same characteristic, properties and composition. Example, Helium and H2O. Pure substances
cannot be separated into different components by physical means.

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Mixture: Matter composed of 2 or more substances that can be easily separated by physical
means and each which retains its own identity and properties. Example, concrete and
saltwater solution. In other words, mixtures can be separated into different components.
Figure 2.8, shows the different between pure substance and mixture.

Figure 2.8, Pure substance versus mixture.

Periodic Table Of Elements

The periodic table of chemical elements, often called the periodic table, organizes all
discovered chemical elements in rows (called periods) and columns (called groups) according
to increasing atomic number. Scientists use the periodic table to quickly refer to information
about an element, like atomic mass and chemical symbol. The periodic table’s arrangement
also allows scientists to discern trends in element properties, including electronegativity,
ionization energy, and atomic radius.

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Figure 2.9, Periodic table of elements

Periodic Table Of Elements Characteristics

1. Consists of 118 elements
2. Vertical columns are named groups (8 groups, I - IIIV)
3. Elements that have the same number of electrons in the outermost shell will be

included in the same group.
4. A list of elements arranged in order of increasing proton number from left to right and

from top to bottom.
5. The horizontal row is called period and there are 7 periods
6. The chemical properties of an atom depend on the number of electrons in the

outermost shell
7. The electrons in the last orbital called electron valence
8. Most of the elements are metals, and only a few are non-metal in solid or liquid or gas

form.
9. Last column on the right of the table is called inert gas where the gases mostly inert to

its environment.

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Usage Of Element Periodic Table

1. To facilitate the classification of elements.
2. Provides information about elements, especially the properties of elements.
3. Provides information on elements that are still being discovered and predicts

properties and uses.
4. It is easy to analyze and understand the reactions between the elements.

Atomic Bonding

All materials are made up of atoms. These atoms are held together by forces called
interatomic bonds. The bonds act like springs, linking each atom to its neighbor.

There are several different types of bonds that form between atoms. The type of bonding
between atoms can give rise to very different properties. For example, graphite and diamond
are both carbon, however, due to the nature of their atomic bonding, they exhibit
exceptionally different material characteristics.

Atomic bonding can be classified into two main groups. The primary and secondary bond.
The Primary bonds involve sharing or donating electrons between atoms to form a more
stable electron configuration. Secondary bonds classified as a weak bond that exist between
molecules or compounds.

Classification Of Atomic Bonding

Between the atoms or molecules, there is a bond that holds the atoms or molecules together.
This bond can be divided into two types, namely, primary bond and secondary bond. The
primary bonds involve sharing or donating electrons between atoms to form a more stable
electron configuration. The secondary bond is a bond that is usually found between
compounds that are easy to break. Premier Bond can be grouped into 3 main groups which
are Ionic Bond, Covalent Bond and Metallic Bond.

Ionic bond

1. Atoms of different elements transfer electrons from one to the other so that both have
stable outer shells and at the same time become ions.

2. The ions are one positively charged and the other negatively charged.

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3. The binding force is strictly electrostatic.
4. No. of +ve charge is equal to no. of –ve charge.
5. The attractive bonding forces are coulombic; that is’ positive and negative ions, by

virtue of their net electrical charge, attract one another.
Example 1: IONIC BONDING Sodium Chloride (NaCl)
Sodium is a metal and has one electron valence. Chlorine is non-metal and has 7 electrons in
the outer shell. Sodium donates one electron to Chlorine, so that its electron complete 8 in the
outer shell such as given Figure 2.10. Since Sodium donates 1 electron, it becomes positive
ion, and Chlorine which receives one electron, it becomes negative ion.

Figure 2.10, Sodium and Chlorine ionic compound

Example 2: IONIC BONDING Magnesium Oxide (MgO)
Magnesium is a metal and has two electrons valence. Oxygen is non-metal and has 6
electrons in the outer shell. Magnesium donates two electrons to Oxygen, so that its electron
complete 8 in the outer shell such as given picture above. Since Magnesium donates 2

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electrons, it becomes positive ion, and Oxygen which receives 2 electrons, it becomes negative
ion.

Figure 2.11, Magnesium and Oxygen ionic compound

Covalent Bond

1. The bond resulting from sharing of a fair valence electrons by two or more atoms.
2. Elements forming molecules with covalent bonding must have four or more valence

electrons that is the carbon, phosphorus, sulphur, chlorine etc.
3. Hydrogen is an exceptional case. It also enters into covalent bond with the mentioned

elements.
4. Stable electrons configurations are assumed by the sharing of electrons between

adjacent atoms.
Example 1: Covalent Bonding Water (H2O)
Hydrogen is non-metal in a gas form and has one electron valence. Oxygen is also a non-
metal, also in gas form and has six electrons in the outer shell. To complete their outer shells
both hydrogen and oxygen needs 2 more electrons. So, 2 atoms hydrogen sharing shows in
Figure 2.12, their atoms with oxygen to complete their both outer shell electrons which is
eight.

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Figure 2.12, Hydrogen and Oxygen with covalent bond
Example 2: Covalent Bonding Methane (C4H)
Carbon is non-metal in a solid form and has four electrons valence. Hydrogen is also a non-
metal, in gas form and has one electron in the outer shell. To complete their outer shells both
hydrogen and carbon needs 4 more electrons. So, 4 atoms hydrogen sharing as show in Figure
2.13, their atoms with carbon to complete their both outer shell electrons which is eight.

Figure 2.13, Hydrogen and Carbon with covalent bond

Metallic Bond

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In metals or metal alloys in solid state, atoms are orderly arranged in lattices. Electron valence
on outer shell attracted to positive charge from nearby atoms. These electrons pop out from
its shell and move freely around the atom’s core or nucleus. The free moving electrons called
sea of electrons.

Figure 2.14, Electrons from outer shell moving freely around its core
Use Lithium (Li) as an example: The lithium atoms lose their outer electron to become a Li+
ion, shows in Figure 2.15. It becomes Li+ as it loses 1 negatively charged electron and so has 1
more positive proton than electron meaning it has an overall positive charge of 1+. (All metal
ions become positively charged when they bond as they all lose electrons).

Figure 2.15, Lithium valence electrons moving freely around its core
After all lithium atoms have become ions there are lots of electrons left over, and these create
a ‘sea of electrons’ throughout the structure it is the attraction between the positive metal ions
and the negative electrons that holds the structure together.

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Crystal Solid Structure

A crystalline solid or crystal consists of atoms arranged in three dimensions in a
repetitive or uniform pattern. Crystals are composed of metals and non -metals. A single
crystal is a solid with uniformly arranged unit cells while a polycrystalline crystal consists of
many single crystals, show in Figure 2.16. Crystals can be seen using an x-ray defractometer.
Solid can be classified into two:
1. Crystalline solid- monocrystalline solid and polycrystalline solid
2. Amorphous/non-crystaline

Figure 2.16: Monocrystalline, polycrystalline and amorphous

Monocrystalline solid

A monocrystalline or single crystal solid has a composition that is composed of a
single crystal throughout and is made up of metal atoms or other materials that are arranged
in such a way that the entire object is best described as a single grain or a continuous crystal.
The arrangement of the atoms in a single crystalline material exhibits a strict order, resulting
in an almost perfect structure. Single crystals exist in nature but are also artificially produced.
Because a monocrystalline solid is a material where the crystal lattice of the sample has
no grain boundaries and is continuous or unbroken up until reaching the very edge of the
sample, it is completely uniform throughout the entire crystal, regardless of size.

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It is for this reason that monocrystalline solids are used as semiconductor materials of the
highest quality. Due to an absence of defects that usually accompany grain
boundaries, monocrystals have unique mechanical and electrical properties. Therefore, they
are widely used for technological applications like optics and electronics. These properties
also make them precious in some gems.

Not surprisingly, the almost perfect crystalline structure yields the highest light-to-electricity
silicon conversion efficiency in solar panels. The primary use for single crystal superalloys is
to manufacture jet engine turbine blades. Galvanic corrosion is induced by the porous silicon
formation found in both monocrystalline and polycrystalline silicon, and results in a thickly
corroded surface layer.

Polycrystalline solid

Not all solids are single crystals (e.g. silicon semiconductors). Most crystalline solids
are composed of a collection of many small crystals or grains of varying size and orientation.
These have random crystallographic orientations. When a metal starts with crystallization,
the phase change begins with small crystals that grow until they fuse, forming
a polycrystalline structure. In the final block of solid material, each of the small crystals
(called “grains“) is a true crystal with a periodic arrangement of atoms, but the whole
polycrystal does not have a periodic arrangement of atoms, because the periodic pattern is
broken at the grain boundaries. Figure 2.16, shows grain and grain boundaries. Grains and
grain boundaries help determine the properties of a material.

Grains also known as crystallites, are small or even microscopic crystals which form,
for example, during the cooling of many materials (crystallization). A very important feature
of a metal is the average size of the grain. The size of the grain determines the properties of
the metal. For example, smaller grain size increases tensile strength and tends to increase
ductility. A larger grain size is preferred for improved high-temperature creep properties.
Creep is the permanent deformation that increases with time under constant load or stress.
Creep becomes progressively easier with increasing temperature.

Grain Boundaries refers to the outside area of a grain that separates it from the other
grains. The grain boundaries separate variously-oriented crystal regions (polycrystalline) in
which the crystal structures are identical. Grain boundaries are 2D defects in the crystal
structure and tend to decrease the electrical and thermal conductivity of the material. Most
grain boundaries are preferred sites for the onset of corrosion and for the precipitation of new

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phases from the solid. They are also important to many of the mechanisms of creep. On the
other hand, grain boundaries disrupt the motion of dislocations through a material.
Dislocation propagation is impeded because of the stress field of the grain boundary defect
region and the lack of slip planes and slip directions and overall alignment across the
boundaries. Therefore, reducing crystallite size is a common way to improve mechanical
strength, because the smaller grains create more obstacles per unit area of slip plane.

Figure 2.17: Grain and grain boundaries

Amorphous/Non-Crystalline Materials

Let’s look at glass, which is basically the definition of a non-crystalline material. Materials
which are not crystalline are called amorphous solids, or glasses. Window glass is the most
common amorphous solid, but obsidian, some kinds of porcelain, and bulk metallic glasses
may also be considered glass because they have a random arrangement of atoms, rather than
a repeating array of atoms. Actually, amorphous solids do not have a definite melting point
and can exist in two different states.

1. Rubbery state
2. Glassy state
Examples: Rubber, glass, wax, butter, polymers etc. Amorphous silicon can be used in solar
cells and thin film transistors. And yet, window glass exists as a crystal, too. Window glass,
shows in Figure 2.18, is SiO2, the same chemical that makes up quartz. The difference between
quartz and glass is that quartz was given time at high temperature to crystallize. Glass was
cooled quickly enough to avoid crystallization. For SiO2 to form a crystal, it actually needs to
cool extremely slowly. Metals may need to be cooled in picoseconds to freeze into a glass
before crystallizing.

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Polymers are also usually non-crystalline. Polymers are different from other materials
because they are not made of atoms, but long molecule chains. These chains can (and often
do) align into an orderly pattern, but this pattern is rarely as perfect as in atomically-bonded
materials like metals and ceramics. Polymers are usually considered “semicrystalline,”
although they can also be completely amorphous.

Figure 2.18: Glass atomic structure

Bravais Lattice

Bravais lattices are a way to describe a repeating arrangement of objects that fill a space.
Bravais lattices are the foundation for crystal structures. All other lattices can simplify into
one of the Bravais lattices. Bravais lattices move a specific basis by translation so that it lines
up to an identical basis. In 3 dimensions, there are 14 Bravais lattices, shows in Figure 2.19:

1. Simple Cubic
2. Face-Centered Cubic
3. Body-Centered Cubic
4. Hexagonal
5. Rhombohedral
6. Simple Tetragonal
7. Body-Centered Tetragonal
8. Simple Orthorhombic
9. Face-Centered Orthorhombic
10. Body-Centered Orthorhombic
11. Base-Centered Orthorhombic

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12. Simple Monoclinic
13. Base-Centered Monoclinic
14. Triclinic

The concept of lattice comes along with the concept of crystals. Crystalline solids have definite
patterns which arise due to the definite patterns in which the different atoms of the crystals
are placed. The definite geometric shapes of crystals are possible due to the formation of a
lattice with a series of atoms arranged in that specific pattern to give a well-designed three-
dimensional structure. The repetitive pattern of the lattice units forms the actual crystal. The
atoms can also be substituted with ions or molecules. Lattice points are the points of finding
the constituent atoms of the crystal.

Figure 2.19: 14 types of Bravais Lattice

Crystal Structure

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Two types of Bravais lattices will discuss here which are, cubic and hexagonal. Three types
of cubic, simple cubic, body center cubic-BCC and face center cubic-FCC. While only one
hexagonal close-packed.

Simple Cubic

Eg : Polonium-Po

Figure 2.20: Simple Cubic
How to calculate no of atom in ONE simple cubic?
8 atoms at each corner X 1/8 section = 1 atom

Body Centered Cubic -BCC

Eg: Chromium-Cr, Ferum-Fe(α), Tungsten-W, Barium- Ba, Molybdenum-Mo

Figure 2.21: Body Center Cubic
How to calculate no of atom in ONE Body Center Cubic?
8 atoms at each corner X 1/8 section = 1 atom
1 atom at center = 1 atom
Total Atom = 2 atom

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Face Center Cubic -FCC

Eg: Alumnum-Al, Copper-Cu , Gold- Au, Nickel- Ni, Silver-Ag

Figure 2.22: Face Center Cubic
How to calculate no of atom in ONE Face Center Cubic?
8 atoms at each corner X 1/8 section = 1 atom
6 atoms at each facet X ½ section = 3 atoms
Total Atom = 4 atoms

Hexagonal Close-packed

cth : Berilium-Be, Magnesium-Mg dan Zinc-Zn

Figure 2.23: Hexagonal Close-packed
How to calculate no of atom in ONE Hexagonal Closed Packed?
12 atoms at each corner X 1/6 section = 2 atom
2 atoms at each facet X ½ section = 1 atom
3 full atom at center of the structure = 3 atom
Total Atom = 6 atoms

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Element and its Crystal Structure

FCC and BCC are two of the most iconic crystal structures. Nearly all elements have FCC,
BCC, or HCP structures. The most direct difference between FCC and BCC crystals is in the
atomic arrangements. The face-centered cubic structure has an atom at all 8 corner positions,
and at the center of all 6 faces. The body-centered cubic structure has an atom at all 8 corner
positions, and another one at the center of the cube. HCP in a different case which HCP atom
arrangement is in hexagonal not cubic. Figure 2.24 below show example of elements and their
crystal structures.

Figure 2.24: Crystal structure of elements at room temperature

Atomic Packing Factor (APF)

Atomic Packing Factor (APF) tells what percent of an object is made of atoms versus
empty space. Can think of this as a volume density, or as an indication of how tightly-packed
the atoms are.

For quick reference, Table 2.7below of atomic packing factor (APF) values
for common crystal structures.

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Table 2.7: Atomic Packing Factor (APF) Atomic Packing Factor
Crystal Structure

Simple Cubic (SC) 52%

Body-Center Cubic (BCC) 68%
Face-Center Cubic (FCC) 74%
Hexagonal Close-Packed (HCP) 74%

Calculating the atomic packing factor for a crystal is simple: for some repeating volume,
calculate the volume of the atoms inside and divide by the total volume.

Usually, this “repeating volume” is just the volume of the unit cell. The unit cell is defined as
the simplest

Assuming all atoms have the same size, and are arranged in a repeating crystal lattice,
where N means number and V means volume.

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BIBLIOGRAPHY

Loganathan, T.M. Lim, Y.K., Sukinder, N.A., Zainun, M.S. Tuah, K.H. Kamarudin, A. Rifai,
E. Shahrudin, K.F. Abdullah, A. Shafei, S., Balakrishnan, P. Hamjah M.K. & Shabudin, A.
DJJ3213 Material Science. Malaysia Polytechnic Sarawak: Politeknik Kuching.
Callister, W.D. & Rethwisch, D.G. (2018). Material Science and Engineering: An Introduction
(10th edition). Asia: John Wiley & Sons
Callister, W.D. & Rethwisch, D.G. (2011). Materials Science and Engineering: SI Version (8th
Edition). Asia: John Wiley & Sons. Sharma, C.P. (2010).
Engineering Materials: Properties and Applications of Metals and Alloys. PHI Learning.
Smith, W.F. (1996). Principles of Materials Science and Engineering (3rd Edition). USA:
McGraw-Hill.
Raymond A. Higgin, W. Bolton. Materials For Engineers & Technicians. 4 th. Edition Elsevier.
ISBN-13: 978-0-7506-6850-7
R. Kesavan, C. Elanchezhian, B. Vijaya Ramnath. Engineering Materials & Metallurgy, 2006
Anuradha Publications. ISBN: 978-81-89638-10-8
Norman E. Dowling. Mechanical Behavior of Materials. Engineering Methods for
Deformation, Fracture & Fatigue. 1993. ISBN: 0-12-579046-8

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