SOME BASIC CONCEPTS OF CHEMISTRY

     1. DEVELOPMENT OF CHEMISTRY

Chemistry, as we understand it today, is not a very old discipline. Chemistry was not studied for its own sake, rather it came up as a result of search for two interesting things:

i. Philosopher’s stone (Paras) which would convert all baser metals e.g., iron and copper into gold.

i i.‘E lex i r of life’ which would grant immortality.

People in ancient India, already had the knowledge of many scientific phenomenon much before the advent of modern

science. They applied that knowledge in various walks of life. Chemistry developed mainly in the form of Alchemy and Iatrochemistry during 1300-1600 CE. Modern chemistry took shape in the 18th century Europe, after a few centuries of alchemical traditions which were

introduced in Europe by the Arabs.

Other cultures – especially the Chinese and the Indian – had their own alchemical traditions. These included much knowledge of chemical processes and techniques. 

In ancient India, chemistry was called

Rasa yan S ha s t r a, Ra stan t r a, R as Kr i ya or  Ra s w id y a. It included metallurgy, medicine, manufacture of cosmetics, glass, dyes, etc. Systematic excavations at Mo hen jo d a  r  o in Sindh and Harappa in Punjab prove that the story of development of chemistry in India is very old. Archaeological findings show that baked bricks were used in construction work. 

It shows the mass production of pottery, which  can be regarded as the earliest chemical process, in which materials were mixed, moulded and subjected to heat by using fire to achieve desirable qualities. Remains of glazed pottery have been found in M oh  en j od  a r o. Gypsum cement has been used in the construction work. It contains lime, sand and traces of C a C O 3. Harappans made fa i en c e, a sort of glass which was used in ornaments. They melted and forgeda variety of objects from metals, such as lead, silver, gold and copper. They improved the hardness of copper for making artefacts by using tin and arsenic. A number of glass objects were found in Maski in South India (1000–900 BC), and Hastinapur and Taxila in North India (1000–200 BCE). Glass and glazes were coloured by addition of colouring agents like metal oxides.

Copper metallurgy in India dates back to

the beginning of chalcolithic cultures in the subcontinent. There are much archeological evidences to support the view that technologies for extraction of copper and iron were developed indigenously.

According to Rigveda, tanning of leather

and dying of cotton were practised during 1000–400 BC. The golden gloss of the black polished ware of northern India could not be replicated and is still a chemical mystery. 

These wares indicate the mastery with which kiln temperatures could be controlled. Kautilya’s Arthashastra describes the production of salt from sea. A vast number of statements and material described in the ancient Vedic literature can be shown to agree with modern scientific findings. Copper utensils, iron, gold, silver ornaments and terracotta discs and painted grey pottery have been found in many

archaeological sites in north India. Sushruta Samhita explains the importance of Alkalies.

The Charaka Samhita mentions ancient

indians who knew how to prepare sulphuric acid, nitric acid and oxides of copper, tin and zinc; the sulphates of copper, zinc and iron and the carbonates of lead and iron.

Rasopanishada describes the preparation of gunpowder mixture. Tamil texts also describe the preparation of fireworks using sulphur, charcoal, saltpetre (i.e., potassium nitrate), mercury, camphor, etc. Nagarjuna was a great Indian scientist. He was a reputed chemist, an alchemist and a metallurgist. His work Rasratnakar deals with

the formulation of mercury compounds. He has also discussed methods for the extraction of metals, like gold, silver, tin and copper. A book, Rsarnavam, appeared around 800 CE. It discusses the uses of various furnaces, ovens

and crucibles for different purposes. It

describes methods by which metals could be identified by flame colour.

Chakrapani discovered mercury sulphide.

The credit for inventing soap also goes to him. He used mustard oil and some alkalies as ingredients for making soap. Indians began making soaps in the 18th century CE. Oil of Eranda and seeds of Mahua plant and calcium carbonate were used for making soap. The paintings found on the walls of Ajanta

and Ellora, which look fresh even after ages, testify to a high level of science achieved in ancient India. Varähmihir’s Brihat Samhita is a sort of encyclopaedia, which was composed in the sixth century CE. It informs about the preparation of glutinous material to be applied on walls and roofs of houses and temples. It was prepared entirely from extracts of various plants, fruits, seeds and barks, which were concentrated by boiling, and then, treated with various resins. It will be interesting to test such materials scientifically and assess them for use.

A number of classical texts, like

Atharvaveda (1000 BC) mention some dye stuff, the material used were turmeric, madder, sunflower, orpiment, cochineal and lac. Some other substances having tinting property were

kamplcica, pattanga and jatuka.

Varähmihir’s Brihat Samhita gives

references to perfumes and cosmetics. Recipes for hair dying were made from plants, like indigo and minerals like iron power, black iron or steel and acidic extracts of sour rice gruel. Gandhayukli describes recipes for making scents, mouth perfumes, bath powders, incense and talcum power.Paper was known to India in the 17th century as account of Chinese traveller I-tsing describes. Excavations at Taxila indicate that ink was used in India from the fourth century. Colours of ink were made from chalk,  red lead and minimum.

It seems that the process of fermentation

was well-known to Indians. Vedas and

Kautilya’s Arthashastra mention about manytypes of liquors.

Charaka Samhita also mentions ingredients, such as barks of plants,

stem, flowers, leaves, woods, cereals, fruits and sugarcane for making Asavas.

The concept that matter is ultimately made of indivisible building blocks, appeared in India a few centuries BCE as a part of

philosophical speculations. Acharya Kanda,

born in 600 BCE, originally known by the

name Kashyap, was the first proponent of the

‘atomic theory’. He formulated the theory of

very small indivisible particles, which he

named ‘Paramãnu’ (comparable to atoms). He

authored the text Vaiseshika Sutras.

According to him, all substances are

aggregated form of smaller units called atoms

(Paramãnu), which are eternal, indestructible,

spherical, suprasensible and in motion in the

original state. He explained that this individual

entity cannot be sensed through any human

organ. Kanda added that there are varieties of

atoms that are as different as the different

classes of substances. He said these

(Paramãnu) could form pairs or triplets, among

other combinations and unseen forces cause

interaction between them. He conceptualised

this theory around 2500 years before John

Dalton (1766-1844).

Charaka Samhita is the oldest Ayurvedic

epic of India. It describes the treatment of

diseases. The concept of reduction of particle

size of metals is clearly discussed in Charaka

Samhita. Extreme reduction of particle size is

termed as nanotechnology. Charaka Samhita

describes the use of bhasma of metals in the

treatment of ailments. Now-a-days, it has been

proved that bhasmas have nanoparticles of

metals.

After the decline of alchemy, Iatrochemistry

reached a steady state, but it too declined due

to the introduction and practise of western

medicinal system in the 20th century. During

this period of stagnation, pharmaceutical

industry based on Ayurveda continued to

exist, but it too declined gradually. It took

about 100-150 years for Indians to learn and

adopt new techniques. During this time, foreign

products poured in. As a result, indigenous

traditional techniques gradually declined.

Modern science appeared in Indian scene in

the later part of the nineteenth century. By the

mid-nineteenth century, European scientists

started coming to India and modern chemistry

started growing.

From the above discussion, you have learnt

that chemistry deals with the composition,

structure, properties and interection of matter

and is of much use to human beings in daily

life. These aspects can be best described and

understood in terms of basic constituents of

matter that are atoms and molecules. That

is why, chemistry is also called the science of

atoms and molecules. Can we see, weigh and

perceive these entities (atoms and molecules)?

Is it possible to count the number of atoms

and molecules in a given mass of matter and

have a quantitative relationship between the

mass and the number of these particles? We

will get the answer of some of these questions

in this Unit. We will further describe how

physical properties of matter can be

quantitatively described using numerical

values with suitable units.

1.1 IMPORTANCE OF CHEMISTRY

Chemistry plays a central role in science and

is often intertwined with other branches of

science.

Principles of chemistry are applicable in

diverse areas, such as weather patterns,

functioning of brain and operation of a

computer, production in chemical industries,

manufacturing fertilisers, alkalis, acids, salts,

dyes, polymers, drugs, soaps, detergents,

metals, alloys, etc., including new material.

Chemistry contributes in a big way to the

national economy. It also plays an important

role in meeting human needs for food,

healthcare products and other material

aimed at improving the quality of life. This

is exemplified by the large-scale production

of a variety of fertilisers, improved variety of

pesticides and insecticides. Chemistry

provides methods for the isolation of life-

saving drugs from natural sources and

makes possible synthesis of such drugs.

Some of these drugs are cisplatin and taxol,

which are effective in cancer therapy. The

drug AZT (Azidothymidine) is used for

helping AIDS patients.

Chemistry contributes to a large extent

in the development and growth of a nation.

With a better understanding of chemical

principles it has now become possible to

design and synthesise new material having

specific magnetic, electric and optical

properties. This has lead to the production

of superconducting ceramics, conducting

polymers, optical fibres, etc. Chemistry has

helped in establishing industries which

manufacture utility goods, like acids,

alkalies, dyes, polymesr metals, etc. These

industries contribute in a big way to the

economy of a nation and generate

employment.

In recent years, chemistry has helped

in dealing with some of the pressing aspects

of environmental degradation with a fair

degree of success. Safer alternatives to

environmentally hazardous refrigerants, like

CFCs (chlorofluorocarbons), responsible for

ozone depletion in the stratosphere, have

been successfully synthesised. However,

many big environmental problems continue

to be matters of grave concern to the

chemists. One such problem is the

management of the Green House gases, like

methane, carbon dioxide, etc. Understanding

of biochemical processes, use of enzymes for

large-scale production of chemicals and

synthesis of new exotic material are some of

the intellectual challenges for the future

generation of chemists. A developing country,

like India, needs talented and creative

chemists for accepting such challenges. To

be a good chemist and to accept such

challanges, one needs to understand the

basic concepts of chemistry, which begin with

the concept of matter. Let us start with the

nature of matter.

1.2 NATURE OF MATTER

You are already familiar with the term matter

from your earlier classes. Anything which has

mass and occupies space is called matter.

Everything around us, for example, book, pen,

pencil, water, air, all living beings, etc., are

composed of matter. You know that they have

mass and they occupy space. Let us recall the

characteristics of the states of matter, which

you learnt in your previous classes.

1.2.1 States of Matter

You are aware that matter can exist in three

physical states viz. solid, liquid and gas. The

constituent particles of matter in these three

states can be represented as shown in Fig. 1.1.

Particles are held very close to each other

in solids in an orderly fashion and there is not

much freedom of movement. In liquids, the

particles are close to each other but they can

move around. However, in gases, the particles

are far apart as compared to those present in

solid or liquid states and their movement is

easy and fast. Because of such arrangement

of particles, different states of matter exhibit

the following characteristics:

(i) Solids have definite volume and definite

shape.

(ii) Liquids have definite volume but do not

have definite shape. They take the shape

of the container in which they are placed.