Elements, Symbols and Valency

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Welcome to class! 

In today’s class, we will be talking about elements, symbols and valency. Enjoy the class!

ELEMENTS, SYMBOLS AND VALENCY

ELEMENTS

An element is a substance which cannot be split into simpler units by an 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

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

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

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 and electricity.             Poor conductors of heat and electricity (except graphite which conducts electricity).
3. Malleable                                                              Brittle
4. Ductile                                                                  Not ductile
5. Shiny                                                                    Not shiny
6. Often very dense (high density)                          Usually less dense (low 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 valences of some elements:

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 an 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.

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

5. The combining power of oxygen is (a)+2 (b)-2 (c)-1 (d)+1
6. Which of the following is a metalloid? (a) sulphur (b) iron (c) silicon   (d) carbon
7. The symbol Au represents (a) silver (b) lead (c) copper (d) gold
8. Which of the following elements is used as a standard in defining valency? (a) oxygen (b) copper (c) carbon (d) hydrogen
9. Which of the following metals is a liquid at room temperature? (a) iron (b) gold (c) tin (d) mercury

THEORY

1. a. Define an element.
2. Write the symbols of the following elements  (i)  Manganese (ii) Caesium     (iii) Cobalt

2. (a) What are metalloids? (b) Give two differences between metals and non-metal

 

In our next class, we will be talking about Compounds and Mixtures.  We hope you enjoyed the class.

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