CHEMICAL BONDING
Week: THREE Date: Time:
Period: Duration: Average age of learners:
Subject: CHEMISTRY Class: SS ONE
Topic: CHEMICAL COMBINATION
Reference materials:
(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA[ 4th Edition] pg58-68
(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO
(3) INTERNET
Instructional materials: PERIODIC TABLE
Entry behavior: The students have been taught how to write electronic configuration
Behavioural objective: At the end of the lesson the students should be able to:
1st PERIOD
Define periodic table
Arrange the first twenty elements in periodic table
2nd PERIOD
Explain Electrovalent bond with relevant example
State the characteristics of electrovalent bond
3rd PERIOD
Explain covalent bond with relevant example
Mention properties of covalent bond
CHEMICAL BONDING
1st PERIOD
STEP I: The teacher explains periodic table to the students
THE PERIODIC TABLE
The periodic table is an organizational chart of elements following a particular pattern. Elements in the periodic table are arranged in horizontal and vertical rows. Each horizontal row is referred to as a period while those elements with similar chemical and physical properties and similar electronic configurations appear in the vertical columns called group. The atoms of elements in the same group have the same number of electrons in their outermost shells.
STEP II: The teacher leads the students to arrange the first twenty elements in periodic table
|
PERIOD |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
0 |
|
1 |
H 1 |
|
|
|
|
|
|
He 2 |
|
2 |
Li 2,1 |
Be 2,2 |
B 2,3 |
C 2,4 |
N 2,5 |
O 2,6 |
F 2,7 |
Ne 2,8 |
|
3 |
Na 2,8,1 |
Mg 2,8,2 |
Al 2,8,3 |
Si 2,8,4 |
P 2,8,5 |
S 2,8,6 |
Cl 2,8,7 |
Ar 2,8,8 |
|
4 |
K 2,8,8,1 |
Ca 2,8,8,2 |
|
|
|
|
|
|
EVALUATION
The teacher evaluates the lesson by asking these questions:
Explain periodic table
Oxygen and calcium is in what group and period
ASSIGNMENT
Read about electrovalent bond
2nd PERIOD
STEP I: The teacher explains chemical combination
CHEMICAL COMBINATION
Chemical combination is the tendency of other elements is to achieve a noble gas structure of a stable outer octect or duplet of electrons. When atoms combine, it is the electrons on the outermost shell of the atoms that react by being exchanged or shared.
STEP II: The teacher classifies the major bond to the students
There are two major bond classifications, each with identifiable sub-groups:
An element will be
chemically reactive if it can get to the stable electronic configuration of an
inert gas, either
• by losing one or two electrons to another atom, or
• by gaining one or two electrons from another atom (at most three), or
• by sharing three or more electrons.
Three Primary Bonds
The
three types of primary bonding reflect these ways in which atoms can group
together by gaining or losing or sharing electrons, so they can get inert gas
electron configurations.
STEP
III: The teacher explains electrovalent bond with relevant examples
Electrovalent Bond
Electrovalent bond is characterized by transfer of electrons from metallic atoms to non-metallic atoms during a chemical reaction, i.e donor acceptor principle
Electrovalent
Bond is also known as Ionic Bond because compound formed is ionic in nature
having polarity. In electrovalent bond one atom loose electron to form positive
ion called cation and another which gain electron to form negative ion called
anion. This type of bond is known as Electrovalent Bond or Ionic Bond.
Example: Salt- NaCl
Na
--------> Na+ +e-
Cl + e- -------->
Cl-
Na+ + Cl- -------->
NaCl
STEP
IV: The teacher states the characteristics of electrovalent bond
Characteristics of Ionic Compounds
1. An ionic compounds, the oppositely charged ions are tightly packed with each other, so these compounds exist in solid state.
2. Due to strong attractive forces between ions a larger amount of energy is required to melt or to boil the compound and hence the melting and boiling point of the ionic compound are generally high.
3. Ionic compounds are soluble in water but insoluble in organic solvents like benzene, CCl4. etc.
4. In the aqueous solution, the ionic compounds are good electrolytes, because in water the inter-ionic forces are so weakened that the ions are separated and free to move under the influence of electric current. Due to this free movement of ions, the ionic compounds conduct electricity in their solutions.
EVALUATION
The teacher assesses the lesson by asking the following questions:
Briefly explain electrovalent bond
State three characteristics of electrovalent bond
3rd PERIOD
STEP I: The teacher explains covalent bond with relevant example
COVALENT BOND
Definition
A link which is formed by the mutual sharing of electrons between two atoms is called covalent bond.
Explanation
In the formation of covalent bond, mutual sharing of electron takes place. This mutual sharing is possible in non-metals, therefore covalent bond is generally formed between the atoms of non-metals.
FACTORS WHICH FAVOUR THE FORMATION OF COVALENT BOND
High ionization energy
High electron affinity
Low/close electronegativity difference between combining atoms
Presence of unpaired electrons
For example
In Cl2 molecule, two atoms of chlorine are combined with each other to form Cl2 molecule. Each atom of chlorine having seven electrons in its valencies shell. These atoms are united with each other by sharing one of its valence electron as shown.
Cl Cl: —-> :Cl :Cl OR Cl – Cl
In this molecule, one shared pair of electrons forms a single covalent bond between two chlorine the atoms. With the formation of a covalent bond the energy of the system is also decreased.
Cl + Cl —-> Cl – Cl ………….. ΔH = – 242 kJ / mole
This released energy lowered the energy of the molecule and the stability of the compound is also increased.
Types of Covalent Bond
There are three main types of covalent bond.
1. Single Covalent Bond
When a covalent bond is formed by sharing of one electron from each atom, that it is called single covalent bond and denoted by (-) single line between the two bonded atoms e.g.
Cl – Cl, H – H, H – Br etc.
2. Double Covalent Bond
In a covalent bond, if two electrons are shared from each of the bonded atom then this covalent bond is called double covalent bond and denoted by (=) two lines e.g.
O = O, O : : O
3. Triple Covalent Bond
When a covalent bond is formed by sharing of three electrons from each atom then this type of covalent bond is called triple covalent bond, and denoted by (≡) three lines between the two bonded atoms e.g.
N : : N :, N ≡ N
The bond distance of multiple bonds are shorter and the bond energies are higher.
STEP II: The teacher states the characteristics of covalent bond
Characteristics of Covalent Compounds
The main characteristics properties of covalent compounds are as follows
1. The covalent compounds exist as separate covalent molecules, because the particles are electrically neutral so they passes solid, liquid or gaseous state. This intermolecular force of attraction among the molecules.
2. Since the covalent compound exist in all the three states of matter so their melting points and boiling point may be high or low.
3. Covalent compounds are non-electrolytes so they do not conduct electricity from their aqueous solution.
4. Covalent compounds are generally insoluble in water and similar polar solvent but soluble in the organic solvents.
EVALUATION
The teacher assesses the lesson by asking the following questions:
Briefly explain Covalent bond
State three characteristics of covalent bond
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