SYMBOLS AND FORMULAE - I

Week:                 Date:                                                         Time:

Period:                                     Duration:                                             Average age of learners:

Subject: CHEMISTRY                                                                           Class: SS ONE

Topic:             SYMBOLS AND FORMULAE - I

Sub topic: Chemical symbols and Formulae.

Reference materials:

(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA

(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO

(3) INTERNET

Instructional materials:

Entry behavior: The students have been familiar with some common element.

Behavioural objective: At the end of the lesson the students should be able to:

Content

SYMBOL OF AN ELEMENT

Scientist all over the world uses the same letters or symbols for names of elements as a convenient system of shorthand. Or put simply, chemical formula of a substance is a representation of that substance using symbols. There are four ways in writing chemical symbols

1. The first letter in the name of the element                                                2. First letter and any other letter in the name

Element

Symbol

 

Element

Symbol

Carbon

C

Manganese

Mn

Oxygen

O

Magnesium

Mg

Hydrogen

H

Chlorine

Cl

Nitrogen

N

Platinum

Pt

Sulphur

S

Zinc

Zn

Phosphorus

P

Cadium

Cd

Iodine

I

 

 

3. use of Latin name                                                                            4. First two letters of the name of the element are used

Elements

Symbol

 

Elements

Symbol

Ferrum (Iron)

Fe

Calcium

Ca

Plumbum (Lead)

Pb

Cobalt

Co

Argentums (Silver)

Ag

Aluminium

Al

Natrium (Sodium)

Na

Helium

He

Aurum (Gold)

Au

Neon

Ne

 Rules for Writing Chemical Formulas

Learning rules for writing chemical formulas: Before learning the rules for writing chemical formulas let us learn the definition of valency and radical with some examples.

Introduction to rules for writing chemical formulas

Valency: Elements combine with one element to form compounds. Each atom has its own capacity of combination. Valency is the combining capacity of an element. It is the number of electrons that are shared, lost or gained in the course of a chemical reaction. These electrons are called valence electrons.

Radical: A radical is defined as a single atom or a group of atoms that behaves as a single unit and possess an electric charge.

Learning Rules for Writing Chemical Formulas:

Chemical formulae:

A chemical formula is the short scientific method of representing one molecule of an element or a compound.

A chemical formula is written using the symbol of the element, the formula of the radical and their valency. The following steps are involved in writing a formula:

1. Write down the symbols of the elements/ions, which combine to form a molecule of the compound, side by side.

2. Write the valencies of the elements /ions as the superscript on the right hand side.

3. Interchange the valencies of the elements /ions and write as the subscript

4. The radical must be written in brackets, before the subscript is written.

5. Whenever applicable, simple ratios of the valencies must be written.

6. The final formula is written without any sign of the charge. The following examples will help you to acquire better knowledge about writing the formulae of com[pounds

 

 

 

Learning Examples Using Rules for Writing Chemical Formulas:

Water                                                     2. Hydrogen sulphide                                          5. Aluminium chloride

                      H1   O2                                                                      H1     S2                                                                      Al3   Cl1

                      H2O                                                      H2S                                                       AlCl3

 3. Sodium carbonate                                          4. Barium chloride

         Na1       (CO3)2                                                                  Ba2     Cl1        

                Na2CO3                                                                   BaCl2

    Presentation of teacher activity:

i.  The teacher defines element and list the first- thirty elements.

ii. The teacher defines a compound with relevant examples.

iii. The teacher explains mixture and their types

Students’ activities:

i. The students chorus the definition of element

ii. The students mention example of compound

iii. The students differentiate between the types of mixture

Evaluation: The teacher evaluates the lessons by asking the following questions:-

(i)                   define element

(ii)                 what are the constituents of calcium hydroxide and potassium iodide

(iii)                Briefly explain a mixture

Assignment 

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