ELEMENTS AND SYMBOLS.

The Concept of an Element

Our world and universe are made up of millions of different substances. We have already seen how these substances can be classified into solids, liquids and gases. However, on close examination, we find that these substances are made up of a number of small elements.

An element can be defined as a substance that cannot, by any known chemical process, be split into two or more simpler substances. This means that elements cannot, by any chemical process, be made to yield substances simpler than themselves. An element is a substance because it has the same composition throughout.

In 1803, a scientist called John Dalton suggested that each element was made up of its own kind of particles. He called these particles the „atoms‟. Therefore, an element is a substance that is made up of only one kind of atoms.

Names and Symbols of Elements

A chemical symbol is the way of representing an element using initial letter(s). There are many different elements as you have seen above. Every element has a name and a symbol to represent it. Some symbols are just a single capital letter, such as H. Others have two letters, the first of which is always a capital, such as Mg.

Rules for assigning chemical symbols to elements

1. Each element is given a different symbol to represent it.

2. Some elements are represented by two letters e.g. Ca (for calcium), Cl (for chlorine), etc.

3. If two letters represent the element, the first letter is always a capital and the second letter is always a small letter e.g. argon (Ar) and helium (He).

4. In order to avoid confusion, some elements have their chemical symbols derived from Latin names


All symbols are recognized and are used by all scientists all over the world. Some examples of elements and their symbols are given in the table below:

Names and Symbols of some Elements

Element	Symbol	Element	Symbol
Aluminium	Al	Bromine	Br
Copper	Cu	Carbon	C
Iron	Fe	Chlorine	Cl
Lead	Pb	Hydrogen	H
Magnesium	Mg	Nitrogen	N
Mercury	Hg	Oxygen	O

Potassium	K	Phosphorus	P
Silver	Ag	Sulphur	S
Sodium	Na	Silicon	Si
Calcium	Ca	Iodine	I
Manganese	Mn	Fluorine	F
Tin	Sn	Gold	Au
Chromium	Cr
Zinc	Zn
Nickel	Ni

It is easy to remember that the symbol for aluminium is Al, and for carbon is C. But some symbols are harder to remember because they are taken from Latin names. For example, potassium has the symbol, K from its Latin name Kalium. Sodium has the symbol, Na from its Latin name Natrium.

See the complete list in the following table. Elements with Latin names.

English name	Latin name	Chemical symbol
Sodium	Natrium	Na
Gold	Aurum	Au
Potassium	Kalium	K
Mercury	Hydrargyrum	Hg
Silver	Argentum	Ag
Antimony	Stibium	Sb

Lead	Plumbum	Pb
Tin	Stannum	Sn
Iron	Ferrum	Fe
Copper	Cuprum	Cu
Tungsten	Wolfram	W

The reason for assigning some elements with Latin names was to avoid confusion among scientists when representing different elements. For example, the symbol for silicon is Si. It could be impossible to represent silicon by the symbol S and at the same time represent the element sulphur by the very symbol, S. 

Similarly, potassium could not be represented by the symbol P that was assigned to phosphorus. So in order to avoid such confusion, scientists decided to use Latin names to represent some elements. In so doing, the anticipated and unnecessary contradiction among scientists from different parts of the world was avoided.

Symbols are particularly useful when more than one atom is present in a substance. For example, hydrogen gas consists of pairs of hydrogen atoms joined together. So hydrogen gas is shown as H2. When more than one atom is joined together like this, we call the substance formed a molecule. 

Atoms making up gases such as hydrogen, oxygen, nitrogen, etc, always exist as molecules. Sulphur exists as a hexagonal ring of eight atoms. Phosphorus exists as a tetrahedron of four atoms. Table below shows some elements that exist as molecules.

Elements that exist as molecules

Element	Atomic symbol	Molecular symbol
Oxygen	O
Nitrogen	N
Hydrogen	H
Sulphur	S

Phosphorus	P
Chlorine	Cl
Fluorine	F
Bromine	Br
Iodine	I

Classification of Elements

Elements can be classified as either metals or non-metals. Metals and non-metals have different physical and chemical properties. This is the criterion used for classification of these elements into metals on one hand and nonmetals on the other hand. Table below summarizes the physical and chemical properties of some common elements.

Properties of some common elements

	Date	of	Metal or non-	Solid, liquid	Melting	Boiling	Density (	g
Element	discovery		metal?	or gas?	point (°C)	point (°C)	cm-3 )
Oxygen	1774		Non-metal	Gas	-219	-183	0.00132
Nitrogen	1772		Non-metal	Gas	-210	-196	0.00117
Carbon	Ancient		Non-metal	Solid	3500	4827	22
Iron	1735		Metal	Solid	1540	3000	7.9
Copper	Ancient		Metal	Solid	1080	2500	9.0
Lead	Ancient		Metal	Solid	327	1744	113
Gold	Ancient		Metal	Solid	1060	2700	193
Silver	Ancient		Metal	Solid	961	2200	10.5

Hydrogen	1766	Non-metal	Gas	-259	-253	0.00008
Aluminium	1825	Metal	Solid	660	2450	27
Zinc	1746	Metal	Solid	419	910	7.1
Mercury	Ancient	Metal	Liquid	-39	357	13.6
Iodine	1811	Non-metal	Gas	114	183	4.9
Chlorine	1774	Non-metal	Gas	-101	-35	0.003
Sodium	1807	Metal	Solid	98	890	0.97
Potassium	1807	Metal	Solid	64	760	0.86
Sulphur	Ancient	Non-metal	Solid	119	444	2.1
Phosphorus	1669	Non-metal	Solid	44	280	1.8

Metals and non-metals

There are 94 naturally occurring elements. Some of them are very rare. Francium, for instance, has never been seen. The radioactive metals neptunium and plutonium, which we make artificially in quite large amounts, only occur in very small (trace) quantities naturally. 

Most of the elements can be classified as metals. The rest are non-metals. To understand these elements better, refer to the Periodic Table of Elements at the back of this book. Classification of elements into metals and non-metals is based on differences between their physical and chemical properties.

Differences between metals and nonmetals are shown in table below.

Mixtures	Compounds

    A. Physical properties

1. The components of a mixture can be separated
by  physical  means,  e.g.  filtering,  magnetic		The components of a compound can be separated by chemical means
separation, decantation, etc		only
2.	The  composition  of  a  mixture  can  vary	Compounds  are  fixed  in  their  compositions  by  mass  of  elements
widely, e.g. a mixture of 20g of sand with 1g of		present, e.g. there are always 2 atoms of hydrogen to 1 atom of oxygen
salt or vice versa.		in a molecule of water
3.	Mixing  is  not  usually  accompanied  by
external effects such as explosion, evolution of		Chemical combination is usually accompanied by one or more of these
heat, or volume change (for gases)		effects
4.	Properties of a mixture are the sum of the	The properties of a compound are quite different from those of its
properties of the individual constituents of the		constituent  elements.  For  example,  water  is  a  liquid  whereas  its
mixture.		constituent elements, hydrogen and oxygen, are both gases.
5. No new substance is produced as the mixture
forms		A new substance is always produced when a compound forms.
B. Chemical Properties
1.	Give basic oxides, that is, oxides which react with acids		Give acidic oxides, that is, oxides which react with bases
2.	Replace hydrogen in acids to form salts		Do not react with acids in this manner
3.	Form positive (+) ions		Form negative (-) ions
4.	Form electrovalent chlorides which are stable in water		Form covalent chlorides which react with water.
5.	Do not react with hydrogen		Form stable compound with hydrogen

There are over 105 different elements known. Of these, 90 have been obtained from the Earth's crust and the atmosphere, and 15 have been artificially made by scientists. From this small band of elements, all other substances on earth are made. 

Elements from Other Substances

Table shows the approximate percentage composition by mass of the elements in the earth's crust, the oceans, and the atmosphere. Can you notice the abundance of oxygen? Analysis of the earth's crust, the oceans, and the atmosphere, reveals that oxygen is the most abundant element on earth, accounting for half the total mass.

Percentage by mass of elements in the earth's crust, oceans and atmosphere

Percentage by mass of elements in the		Percentage by mass of elements in		Percentage by mass of elements in th
earth’s crust		the oceans		atmosphere
Oxygen	47	Oxygen	86	Nitrogen	75.5
Silicon	28	Nitrogen	10.9	Oxygen	23
Aluminium	7.8	Chlorine	1.8	Argon	1.4
Iron	4.5	Sodium	1.0	Hydrogen	0.02
Calcium	3.5	Magnesium	0.1	Carbon	0.01
Sodium	2.5	Calcium	0.05	Others( total)	0.07
Potassium	2.5	Sulphur	0.05
Magnesium	2.0	Potassium	0.04
Titanium	0.5	Nitrogen	0.02
Hydrogen	0.2	Bromine	0.01
Carbon	0.2	Carbon	0.01
Others( total)	1.3	Others (total)	0.02