Week 4 – SS1 First Term Chemistry Notes

 
 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

2. 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 S0₄^2-, C0₃^2-, 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)         C0₃^2-                -2
Tetraoxosulphate(VI) S0₄^2-                -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) S0₄^2- 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