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.

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

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

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

How many elements are discovered now?
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

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

and electricity (except graphite which conduct electricity)

Malleable Brittle
Ductile Not ductile
Shiny Not shiny
Often very dense Usually less dense(low density)

(high density)

EVALUATION

What are metalloids?
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

Define (i) valency (ii) Radical
Write the valency of: a) Oxygen (b) Potassium c) Sulphur d) S0₄^2- e) NH₄⁺
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

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

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

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

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

THEORY

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

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