CONTENT

• ELEMENTS AND SYMBOLS
• CLASSIFICATION OF ELEMENTS
• VALENCY

ELEMENTS AND SYMBOLS

An element is a substance that cannot be split into simpler units by ordinary chemical processes. 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 is written in capital letters and one other letter from its name is written in small letters.

Element                                       Symbol

Chlorine                                        Cl

Bramine                                         Br

Calcium                                         Ca

Aluminium                                      Al

Magnesium                                    Mg

Berylium                                         Be

Helium                                            He

Neon                                              Ne

Lithium                                           Li

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 have been 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, sulfur, fluorine, and hydrogen, among others.

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

6. Often very dense                              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 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 elements 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 reacts 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

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.
2.  Write the symbols of the following elements

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

3 a. What are metalloids? b. Give two differences between metals and non-metals