Greek Philosophers’ Concept of Matter
Greek philosophers believed that everything in the universe is made of a basic substance called an element. Some thought that this element was water, while others believed it was air. They tried to explain the nature of matter using simple ideas, although these were not based on experiments.
Corpuscular Theory of Matter
The corpuscular theory states that matter is made up of very small particles called corpuscles. Greek philosophers like Empedocles and Democritus presented this idea in the 5th century BC. This theory laid the foundation for modern atomic theory.
Views of Empedocles, Plato and Aristotle
Empedocles suggested that all matter is made up of four basic elements: earth, air, water, and fire. Plato supported this idea and named these substances as elements. Aristotle further explained that these elements are formed by combining four qualities: hot, cold, wet, and dry. These ideas remained important for many centuries.
Definition of Chemistry
Chemistry is a branch of science that deals with the study of matter, its composition, properties, and the changes it undergoes. It helps us understand the substances around us and how they react with each other.
Statements for Each Branch of Chemistry
- Analytical Chemistry
Analytical chemistry helps in determining the composition and purity of substances. For example, elemental analysis shows the elements present in ammonia, and experiments are performed to determine the percentage purity of glucose. Measuring melting point is also an important analytical method.
- Biochemistry
Biochemistry studies chemical processes in living organisms. Photosynthesis in plants produces food using sunlight, and proteins like keratin are found in hair and nails. Many chemical reactions occur inside the human body to maintain life.
- Environmental Chemistry
Environmental chemistry deals with the impact of chemicals on the environment. Pollutants like nitrogen dioxide and sulphur dioxide cause acid rain, and vehicle exhaust gases pollute the air. Plantation helps reduce the greenhouse effect and protect the environment.
- Inorganic Chemistry
Inorganic chemistry focuses on substances other than carbon compounds. Ammonia is an example of an inorganic compound, and metals like silver can react with air and tarnish. This branch studies properties of metals, minerals, acids, bases, and salts.
- Industrial Chemistry
Industrial chemistry involves large-scale production of chemicals. The Haber process is used to manufacture ammonia, and cement is produced in industries using chemical processes. Metals are extracted from ores and used in various industries.
- Nuclear Chemistry
Nuclear chemistry studies changes in the nucleus of atoms. Radioactive elements emit radiation and can change into other elements. Carbon-14 is formed in the atmosphere and is used for dating ancient materials.
- Organic Chemistry
Organic chemistry deals with carbon-containing compounds. Acetic acid is prepared from ethanol, and hydrocarbons like acetylene consist of carbon and hydrogen. Some organic compounds, like dynamite, release gases during chemical reactions.
- Physical Chemistry
Physical chemistry explains the laws and principles of matter. It studies changes of state, compression of gases, and energy changes. For example, iodine changes directly from solid to gas, and ice floats on water due to lower density.
How Archimedes (Greek philosopher) explained the purity of gold of the crown of a Greek emperor of his times? Ans. Archimedes was a Greek philosopher and mathematician. The Greek emperor gave him a task to check the purity of his crown made of gold. One day Archimedes was taking bath and he observed that as he went deep in water, more volume (weight) of water was overflowed from bath tank. He put a piece of gold in water in a pot. It displaced some water from there. He thought that the purity of gold could be determined from the amount (volume) of liquid water it displaced (overflowed) from the pot. He meant that the quantity of water displaced by gold is equal to the weight of the gold piece dipped in it. He knew that if the crown was pure, then the amount of water displaced by it from a pot must be equal to the water displaced by equal weight of pure gold in another pot filled with same quantity of water. He was very much excited by this thinking and ran from there shouting “Eureka” which means “I found it”.
Questions & Answers
Q 1. What was the concept or belief of Greek philosophers about matter (universe)? Ans: Greek philosophers believed that everything was made of an elemental substance. Some of them believed that elemental substance is water, others thought that elemental substance is air.
Q 2. Define corpuscular theory of matter. Ans: Corpuscular theory tells us that matter (universe) is made up of small particles (things). Two Greek philosophers named Empedocles and Democratus presented this theory in 5th century B.C.
Q 3. What was the concept of Greek philosophers (Empedocles, Plato and Aristotle) about corpuscular theory of matter? Explain. Ans. Ancient Greek philosophers presented different concepts about corpuscular theory as follows. i. Empedocles theory. A Greek philosopher, named Empedocles, was the first to say that all matter is made of four things, called earth, air, water and fire. ii. Plato theory. Plato followed Empedocles theory and called these four things elements. iii. Aristotle theory. Aristotle was another Greek philosopher (student of Plato) who adopted the same concept of four elements. But he added that these four elements are made of other four opposite elements called hot-cold and dry-wet. These four elements combine in pairs to form air, fire, water and earth. For example, fire is formed from hot and dry, air is formed from hot and wet, water is formed from cold and wet and earth is formed from wet and dry. This concept of Greeks remained applicable for more than 2000 years.
Q 4. Define chemistry. Ans. It is the branch of science which deals with the study (examination) of matter and changes in matter.
Q 5 Define different branches of chemistry. Ans. The following are different branches of chemistry. i. Analytical chemistry: It is that branch of chemistry which deals with the study of methods and instruments used for determination of composition of matter. ii. Biochemistry: It is that branch which deals with the study of chemical and physical changes taking place inside living things. iii. Environmental chemistry: It deals with the studies of harmful effects of chemicals on environment and human beings. iv. Inorganic chemistry: It deals with the study of elements and compounds other than organic compounds. v. Industrial chemistry: It deals with the studies of methods and technology used for the large scale preparation of products in industries. vi. Nuclear chemistry: It deals with the changes in nuclei of atoms in various substances. [nuclei is plural of nucleus]. vii. Organic chemistry: It studies substances having carbon in them, except carbon monoxide (CO),carbon dioxide (CO2),carbonates (CO2-3) and bicarbonates (HCO1-3). viii. Physical chemistry: It studies laws and theories to understand structure and changes in matter.
Q 6 Write down different statements against each branch of chemistry to justify its definition. Ans. (a) Analytical Chemistry. i. Elemental analysis shows that ammonia contains nitrogen and hydrogen elements. ii. Acetic acid is composed of carbon, hydrogen and carbon elements only. iii. Gasoline fumes are burnt in automobile engine to give energy. iv. Calorimeter is a device used to measure the amount heat a substance absorbs on heating or emits on cooling. v. Sulphuric acid is weaker acid than hydrochloric acid. vi. Melting point of sodium chloride is 801oC measured by Fisher-Johns Apparatus. vii. A chemist did an experiment to determine percentage purity of a sample of glucose.
(b) Biochemistry. i. Acetic acid causes so many chemical reactions inside human body. ii. Photosynthesis is a natural process used for production of food inside plants in presence of sunlight and chlorophyll. iii. Hair and nails contain keratins (proteins). iv. A cornstalk grows from a seed. v. Some examples of complete protein food are meat, milk and eggs.
(c) Environmental Chemistry. i. Nitrogen dioxide (NO2) is responsible for acid rain. ii. Excessive drink of acetic acid causes adverse/harmful effects on human health. iii. Vehicles exhaust gases pollute the air or atmosphere. iv. Sulphur dioxide is the major source of acid rain. v. Chlorofluorocarbons are responsible for ozone depletion. vi. Plantation helps in overcoming green house effect. vii. Light chlorinated hydrocarbons in drinking water are carcinogens (cancer causing).
(d) Inorganic Chemistry. i. Ammonia is soluble in water. It has no colour and has pungent irritating smell. i ii. A silver article tarnishes in air.
(e) Industrial Chemistry. i. Haber’s process is used for large scale production of ammonia. ii. White lead is a pigment used by artists for centuries which is extracted from its ore, galena (PbS). iii. In Pakistan, most industries use wet process for cement production.
(f) Nuclear Chemistry. i. Bombardment of alpha rays or neutrons on compounds brings about nuclear changes. ii. The element radium is converted into radon by emitting α-particles. iii. Carbon-14 is continuously produced in the atmosphere when high energy neutrons from space collide with nitrogen-14.
(g) Organic Chemistry. i. Acetic acid is compound of carbon and is prepared from organic compound called ethyl alcohol (C2H5OH). ii. The study of carbon, oxygen and hydrogen elements in acetic acid (CH3COOH). iii. Acetylene is hydrocarbon composed of carbon and hydrogen elements iv. Dynamite (C3H5N3O9) explodes to form a mixture of gases. v. Acetic acid is prepared by oxidation of ethyl alcohol.
(h) Physical Chemistry. i The study of how the rate of a chemical reaction increases when the temperature is raised. ii. By increasing temperature of a gas sample, the volume increases. iii. The change of solid to gas, gas to liquid or liquid to solid or solid to liquid etc. iv. Gases can be compressed by applying pressure. v. Purple iodine vapours appear when solid iodine is warmed. vi. Ice floats on water.
Q 7.