CHEMICAL BONDING

 

Week:   FOUR                      Date:                                                   Time:

Period:                                   Duration:                                           Average age of learners:

Subject:                               CHEMISTRY                                                         Class:  SS ONE

Topic:                                                    CHEMICAL COMBINATION

Sub – Topic:   Dative bond, Metallic bond and secondary bond

Reference materials:

(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA[ 4^th 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:

1^st PERIOD

Explain dative bond with relevant examples

Explain metallic bond with relevant examples

2^nd  PERIOD

Explain Hydrogen bond with relevant example

Explain Van der waal forces  with relevant examples

 3^rd PERIOD

                Revision on chemical combination

CHEMICAL BONDING (continue)

1^st PERIOD

STEP I: The teacher explains co-ordinate bond with relevant example

Co-ordinate Bond / Dative bond

Certain atoms which have complete octets can donate their valence electrons which are not involved in bond formation ,to other atoms, which are short of electron. These donated electrons are, therefore, lone pair of electrons and are shared by both the atoms.

When in the formation of a bond, the electron pair is donated by one atom but shared by both the atoms so as to complete their octets, the bond formed is called co-ordinate bond or dative bond.

Bond is represented by an arrow pointing from the donor to the acceptor.

Bond has some polar character, it is also known as dative or semi-polar bond or co-ionic bond.

FACTORS WHICH FAVOUR THE FORMATION OF DATIVE BOND

Vacant/empty orbital in one atom

Presence of lone pair of electrons (in another)

Example of dative bond
1)Ammonia with Boron trifluoride

In ammonia, nitrogen has 5 valence electrons. Out of these ,3 electrons are shared by 3 hydrogen atoms to form ammonia molecule while the remaining two electrons form a lone pair, which can be donated to any electron deficient atom or molecule.

In BF₃ molecule, boron is short of 2 electron.So to complete its octet,  it shares the lone pair of nitrogen ,forming a dative bond.

2)Sulphur dioxide

Sulphur as well as oxygen atoms have 6 valence electrons and each is a short of 2 electrons to complete its octet. Sulphur atom and oxygen atom ,share two electrons each thus forming a double bond between them .Sulphur atom still has 4 unshared electrons i.e. two lone pairs to donate.Sulphur donates 1 lone pair to oxygen atom, forming a co-ordinate bond between sulphur and a molecule of Sulphur dioxide.By accepting this lone pair, octet of oxygen is also completed.

STEP II: The teacher explains Metallic bond with relevant example

METALLIC BOND

 Metallic bonds are strong, so metals can maintain a regular structure and usually have high melting and boiling points.

 

Atomic structure of a metal

Metals are good conductors of electricity and heat, because the free electrons carry a charge or heat energy through the metal. The free electrons allow metal atoms to slide over each other, so metals are malleable and ductile.

EVALUATION

The teacher assesses the lesson by asking the following questions:

Briefly explain co-ordinate bond

Explain metallic  bond

 

2^nd PERIOD

STEP I : The teacher explains Hydrogen bond with relevant example

HYDROGEN BOND

 A hydrogen bond is a special type of dipole-dipole attraction which occurs when a hydrogen atom bonded to a strongly electronegative atom exists in the vicinity of another electronegative atom with a lone pair of electrons. These bonds are generally stronger than ordinary dipole-dipole and dispersion forces, but weaker than true covalent and ionic bonds. Without hydrogen, bonding earth would have no water cycle, no ocean, no floating ice, no life as we know it.

In order for a hydrogen bond to occur, there must be both a hydrogen donor and an acceptor present. The donor in a hydrogen bond is the atom to which the hydrogen atom participating in the hydrogen bond is covalently bonded, and is usually a strongly electronegative atom such as N, O, or F. The hydrogen acceptor is the neighboring electronegative ion or molecule and must possess a lone-pair electron in order to form a hydrogen bond.

Since the hydrogen donor is strongly electronegative, it pulls the covalently bonded electron pair closer to its nucleus, and away from the hydrogen atom. The hydrogen atom is then left with a partial positive charge, creating a dipole-dipole attraction between the hydrogen atom bonded to the donor, and the lone electron pair on the acceptor.

STEP II: The teacher explains Van der waal’s forces with relevant example

 Van der Waals' forces

Van der Waals' forces are forces of attraction which exist between all atoms and molecules. Van der Waals' forces are much weaker than all other types of bonding.

They are only significant in atoms and molecules which have no other types of intermolecular forces of attraction, for example, discrete non-polar molecules and the Group 0 elements.

Van der Waals' forces are a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.

The strength of Van der Waals' forces is related to the size of atoms and molecules. The bigger the atom or molecule the bigger the Van der Waals' force.

 EVALUATION

The teacher assesses the lesson by asking the following questions:

Briefly explain Hydrogen bond

Explain van dan waal’s forces