Lesson Notes By Weeks and Term - Senior Secondary School 1

TERM: FIRST TERM

SUBJECT: CHEMISTRY

CLASS: SS 1

REFERENCE MATERIALS

• New School Chemistry for Senior Secondary School by Osei Yaw A.
• Practical Chemistry for Schools and Colleges by G. O. Ojokuku
• Calculation in Chemistry by E.U. Akusoba and G.O Ewelukwa
• WASSCE Past Questions and Answers on Chemistry
• UTME Past Questions and Answers on Chemistry

WEEK FOUR

TOPIC:  ELEMENTS, SYMBOLS & VALENCY

CONTENT

• ELEMENTS AND SYMBOLS
• CLASSIFICATION OF ELEMENTS
• VALENCY

ELEMENTS AND SYMBOLS

An element is a substance which cannot be split into simpler units by ordinary chemical process. There are over one hundred known elements.

SYMBOLS OF ELEMENTS

There are three ways in which symbols of elements are derived.

1. From the first letter of the name of the element

Element                Symbols

Hydrogen            H

Oxygen                  O

Iodine                I

Fluorine            F

Nitrogen            N

Sulphur                  S

Carbon                C

Phosphorus            P

1. The first letter written in capital letter and one other letter from its name written in small letter.

Element            Symbol

Chlorine            Cl

Bramine            Br

Calcium            Ca

Aluminium            Al

Magnesium            Mg

Berylium            Be

Helium                He

Neon                Ne

Lithium            L

1. The symbols of some elements were derived from their Latin names.

Elements    Latin name         Symbols

Mercury    Hydragyrium        Hg

Sodium        Natrium        Na

Iron        Ferrum            Fe

Copper        Cuprum        Cu

Silver        Argentum        Ag

Tin        Stannum        Sn

Gold        Aurum            Au

Potassium    Kalium            K

Lead        Plumbum        Pb

EVALUATION

1.  How many elements are discovered now?
2. Write the symbols for the following elements: silicon, iodine, fluorine, sulphur, silver, Iron, copper, potassium and sodium.

CLASSIFICATION OF ELEMENTS

Elements can be classified into metals and non-metals.

Examples of metals include iron, zinc, tin, aluminium, copper etc.

Examples of non-metals are: Chlorine, oxygen, sulphur, fluorine, hydrogen etc.

Some elements however possess the properties of metals as well as non-metals. They are called metalloids, examples are silicon and germanium.

THE DIFFERENCES BETWEEN METALS AND NON-METALS

Metal                    Non – metals

1. They are solids (except mercury)   They are solids, liquids and gases
2. Good conductors of heat           Poor conductors of heat and electricity

and electricity                               (except graphite which conduct electricity) 

3. Malleable                     Brittle
4. Ductile             Not ductile
5. Shiny                         Not shiny

1. Often very dense                     Usually less dense(low density)

(high density)  

EVALUATION

1. What are metalloids?
2. State two differences between metals and non-metals.

VALENCY

Valency is the combining power of an element. It can also be defined as the number of hydrogen atoms that can combine with or replace one atom of that element.

Valency of an element depends on the structure of that element. At times it corresponds to the number of electrons in the outermost shells called valence electrons.

Below are the valencies of some elements:

Element            Symbol            Valency

Aluminium            Al                +3

Argon                Ar                Nil

Calcium            Ca                +2

Chlorine            Cl                -1

Sulphur            S                        -2, -4 or -6

Sodium            Na                +1

Magnesium            Mg                +2

Copper                Cu                +1 or +2

Carbon                C                -2 or -4

Barium                Ba                +2

Silver                 Ag                +1

Iron                Fe                +2 or +3

Valencies have either positive or negative values showing whether electrons are gained or lost. If an element gains electrons, its value is negative but positive when it loses electrons.

Generally, metals exhibit positive valencies while non – metal tend to have negative valencies. Some element exhibit more than one valency. Valency can also be called oxidation number or state.

RADICALS

A radical is a group of atoms having an electric charge either positive or negative which keeps its identity and react as a single unit. Any small group of atoms carrying a negative charge is called an acid radical. Examples of acid radicals include S042-, C032-, N03-

The valency of a radical corresponds to the charge it carries.

Radical                Formula            Valency

Ammonium                NH4+                      +1

Hydroxide                      0H-                -1

Trioxonitrate(V)                  N03-                -1

Dioxonitrate(III)                  N02-                -1

Trioxocarbonate(IV)                  C032-                -2

Tetraoxosulphate(VI)                    S042-                -2

Hydrogen trioxocarbonate            HC03-                -1

GENERAL EVALUATION/REVISION

1. Define (i) valency (ii) Radical
2. Write the valency of: a) Oxygen (b) Potassium c) Sulphur d) S042- e) NH4+ 
3. Classify the following into physical or chemical changes: a) Rusting of iron b) Fermentation of palm wine c) Evaporation of a salt solution d) Melting of ice

READING ASSIGNMENT

• New School Chemistry for SSS by O.Y Ababio. Pg 26, 32-33

WEEKEND ASSIGNMENT

1. The combining power of oxygen is (a)+2 (b)-2 (c)-1 (d)+1
2. Which of the following is a metalloid?  (a) sulphur (b) iron (c) silicon   (d) carbon
3. The symbol Au represents (a) silver (b) lead (c) copper (d) gold
4. Which of the following elements is used as a standard in defining valency?

           (a) oxygen (b) copper (c) carbon (d) hydrogen

1. Which of the following metals is a liquid at room temperature?

1. iron (b) gold (c) tin (d) mercury

THEORY

1. a. Define an element.

1.     Write the symbols of the following elements

(i)  Manganese (ii) Caesium     (iii) Cobalt 

2. a. What are metalloids?

1.     Give two differences between metals and non-metal