ELEMENTS, SYMBOLS & 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
6. 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

 

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

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

• 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?
3. Give two differences between metals and non-metal

 

See also

NATURE OF MATTER

LABORATORY FAMILIARIZATION

INTRODUCTION TO CHEMISTRY

ELECTROLYSIS

APPLICATIONS OF ELECTROCHEMICAL CELLS