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Chemical Bonding An over view
Technical Report · March 2019
DOI: 10.13140/RG.2.2.22915.76329/4
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CHEMICAL BONDING: AN OVERVIEW
Submitted by; AbdAl-Rhman Magdy Abdullah Youssef
Department of chemical engineering, Higher Technological Institute-Tenth of Ramadan City, Egypt
ID: 20160517
Submitted to; Dr. Mosaad Sadawy
Lecturer of mining Engineering
Submission Date; April 2019
Abstract
Chemical compounds formulated by linking it together, this liking done by bonds which classified into
chemical (Primary) and physical (Secondary) bonds. In this research the first one will be discussed with sum details.
Chemical bonds have three types; ionic, covalent, and metallic.
The ionic bond formulated by donation of valance electron from element which changed to positive ion to
another element which changed to negative ion, (NaCl) is a clear example on ionic bond. On the other hand, the
covalent bond formulated by sharing of valance electrons between adjacent elements, methane is a clear example
on covalent bond. Hydrogen and carbon share valance electrons to complete each one orbital. Metals atoms have
from 1 to 3 valance electrons, these electrons not shared or donated between elements but form a cloud which
have negative charge, and the rest of element electron form the ion core which have positive charge, the
mentioned cloud act as glue for bounding between those ion cores metals alloys is a clear example on metallic
bond.
I. Introduction
attractive and repulsive components, which obtained
in equation (1);
FN =FA +FR………………………………………. equation (1)
which is also a function of the interatomic separation,
When FA and FR balance, or become equal, there is no
net force, which obtained in equation (2);
FA + FR = 0……………………………………………equation (2), [2]
There are four important mechanisms by which
atoms are bonded in engineered materials. These are;
metallic bonds, covalent bonds, ionic bonds and van
der Waals bonds.
The first three types of bonds are relatively
strong and are known as primary bonds (relatively
strong bonds between adjacent atoms resulting from
the transfer or sharing of outer orbital electrons). The
van der Waals bonds are secondary bonds and
originate from a different mechanism and are relatively
weaker, [1].
III. Types of Chemical Bonds
Primary or chemical bonds are found in solids—
ionic, covalent, and metallic. For each type, the
bonding necessarily involves the valence electrons;
furthermore, the nature of the bond depends on the
electron structures of the constituent atoms. In
general, each of these three types of bonding arises
from the tendency of the atoms to assume stable
electron structures, like those of the inert gases, by
completely filling the outermost electron shell, [2].
II. Bonding Forces and Energies
An understanding of many of the physical
properties of materials is predicated on a knowledge of
the interatomic forces that bind the atoms together.
Perhaps the principles of atomic bonding are best
illustrated by considering the interaction between two
isolated atoms as they are brought into close proximity
from an infinite separation.
At large distances, the interactions are
negligible, but as the atoms approach, each exerts
forces on the other. These forces are of two types,
attractive and repulsive, and the magnitude of each is
a function of the separation or interatomic distance.
The origin of an attractive force FA depends on the
particular type of bonding that exists between the two
atoms. The magnitude of the attractive force varies
with the distance ultimately, the outer electron shells
of the two atoms begin to overlap, and a strong
repulsive force FR comes into play. The net force FN
between the two atoms is just the sum of both;
1- Ionic Bonds
When more than one type of atom is present in
a material, one atom may donate its valence electrons
to a different atom, filling the outer energy shell of the
second atom. Both atoms now have filled (or emptied)
outer energy levels, but both have acquired an
electrical charge and behave as ions. The atom that
contributes the electrons is left with a net positive
charge and is called a cation, while the atom that
accepts the electrons acquires a net negative charge
and is called an anion. The oppositely charged ions are
then attracted to one another and produce the ionic
bond. For example, the attraction between sodium and
1
3- Metallic Bonds
chloride ions (Figure1) produces sodium chloride
(NaCl), or table salt, [1].
the final primary bonding type, is found in metals
and their alloys. A relatively simple model has been
proposed that very nearly approximates the bonding
scheme. Metallic materials have one, two, or at most,
three valence electrons. With this model, these valence
electrons are not bound to any particular atom in the
solid and are more or less free to drift throughout the
entire metal. They may be thought of as belonging to
the metal as a whole, or forming a “sea of electrons” or
an “electron cloud.”
Figure (1): An ionic bond is created between two unlike
atoms with different electronegativities. When sodium
donates its valence electron to chlorine, each becomes an
ion, attraction occurs, and the ionic bond is formed, [1].
The remaining non-valence electrons and atomic
nuclei form what are called ion cores, which possess a
net positive charge equal in magnitude to the total
valence electron charge per atom. Figure (3) is a
schematic illustration of metallic bonding. The free
electrons shield the positively charged ion cores from
mutually repulsive electrostatic forces, which they
would otherwise exert upon one another;
consequently, the metallic bond is nondirectional in
character. In addition, these free electrons act as a
“glue” to hold the ion cores together, [2].
Sodium chloride (NaCl) is the classic ionic
material. A sodium atom can assume the electron
structure of neon (and a net single positive charge) by
a transfer of its one valence 3s electron to a chlorine
atom. After such a transfer, the chlorine ion has a net
negative charge and an electron configuration identical
to that of argon. In sodium chloride, all the sodium and
chlorine exist as ions. This type of bonding is illustrated
schematically in Fig. (1), [2].
2- Covalent Bonds
In covalent bonding, stable electron
configurations are assumed by the sharing of electrons
between adjacent atoms. Two atoms that are
covalently bonded will each contribute at least one
electron to the bond, and the shared electrons may be
considered to belong to both atoms. Covalent bonding
is schematically illustrated in Figure 2 for a molecule of
methane. The carbon atom has four valence electrons,
whereas each of the four hydrogen atoms has a single
valence electron.
Each hydrogen atom can acquire a helium
electron configuration (two 1s valence electrons) when
the carbon atom shares with it one electron. The
carbon now has four additional shared electrons, one
from each hydrogen, for a total of eight valence
electrons, and the electron structure of neon. The
covalent bond is directional; that is, it is between
specific atoms and may exist only in the direction
between one atom and another that participates in the
electron sharing, [2]
Figure (3): The metallic bond forms when atoms give up their
valence electrons, which then form an electron sea. The
positively charged atom cores are bonded by mutual
attraction to the negatively charged electrons, [1].
VI. References
1. [1] Cengage Learning, Donald R. Askeland, Pradeep
P. Fulay, Wendelin J. Wright, "The Science and
Engineering of Materials", Sixth Edition, 2010, Pages
34, 35, 37, 38.
2. [2] John Wiley & Sons, William D. Callister, Jr.,
"Materials Science and Engineering An Introduction",
Seventh Edition, 2007, Pages 24, 25,26,27,28,29.
Figure (2): Schematic representation of covalent bonding
in a molecule of methane, [2].
2
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