General Science

Introductory General Science

The laws and principles of science find application, not only in daily life but also in every walk of life. As a result Science and Technology have become an integral part of human life and culture.

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Acids, Bases and Salts

Acids

Curd, lemon juice, orange juice and vinegar taste sour (खट्टा). These substances taste sour because they contain acids.

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Chemical Bonding

Atoms having 8 electrons in their outermost shell are very stable and they did not form compounds. Other atoms such as hydrogen, sodium, chlorine etc. which do not have 8 electrons in their outermost shell undergo chemical reactions. They can stabilize by combining with each other and attain the above configurations of noble gases i.e. 8 electrons (or 2 electrons in case of helium) in their outermost shells.

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Periodic Classification of Elements

Before the beginning of the eighteenth century, only a few elements were known, so it was quite easy to study and remember the properties of those elements and their compounds individually. However, by the middle of the nineteenth century, more the than sixty elements had been discovered.

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Modern Periodic Table

The periodic table based on the modern periodic law is called the Modern Periodic Table. Presently, the accepted modern periodic table is the Long Form of Periodic Table. It may be regarded as an extended form of Mendeleev’s table in which the subgroups A and B have been separated.

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Modern Periodic Law

Though Mendeleev’s periodic table included all the elements, yet at many places a heavier element had to be placed before a lighter one. Such pairs of elements (called anomalous pairs) violated the periodic law. Also, there was no place for different isotopes of an element in the periodic table.

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Mendeleev's Periodic Law and Periodic Table

D'mitri Mendeleev, a Russian chemist, studied the properties of all the 63 elements known at that time and their compounds. On arranging the elements in the increasing order of atomic masses, he observed that the elements with similar properties occur periodically.

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Newlands' Law of Octaves

In 1864, an English chemist John Alexander Newlands arranged the elements in the increasing order of their atomic masses (then called atomic weight). He observed that every eighth element had properties similar to the first element. Newlands called it the Law of Octaves.

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Dobereiner's Triads

In 1829, J.W. Dobereiner, a German chemist made groups of three elements each and called them triads. All three elements of a triad were similar in their physical and chemical properties. He proposed a law known as Dobereiner's law of triads.

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Need for Classification of Elements

Before the beginning of the eighteenth century, only a few elements were known, so it was quite easy to study and remember the properties of those elements and their compounds individually. However, by the middle of the nineteenth century, more than sixty elements had been discovered.

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Valency

Different elements have different number of electrons in the outermost or the valence shell. These electrons in the outermost shell are known as valence electrons. The number of valence electrons determines the combining capacity of an atom in an element.

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Electronic Configuration

The electrons move in definite paths called orbits or shells around a central nucleus. These orbits or shells have different energies and can accommodate different number of electrons in them. The question arises that how are the electrons distributed among these shells? The answer to this question was provided by Bohr and Bury.

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Atomic Number and Mass Number

The nucleus of atom contains positively charged particles called protons and neutral particles called neutrons. The number of protons in an atom is called the atomic number and is denoted by the symbol Z. All atoms of an element have the same atomic number.

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Discovery of Neutron

Rutherford's model was unable to explain the relationship between the atomic mass and the atomic number (the number of protons). According to the Rutherford’s model, the mass of helium atom (containing 2 protons) should be double that of a hydrogen atom (with only one proton).

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Bohr's Model of Atom

In 1913, Niels Bohr, a student of Rutherford proposed a model to account for the shortcomings of Rutherford's model. Bohr's model can be understood in terms of two postulates proposed by him.

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Rutherford’s Model

Ernest Rutherford and his co-workers were working in the area of radioactivity. They were studying the effect of alpha (α) particles on matter. The alpha particles are helium nuclei, which can be obtained by the removal of two electrons from the helium atom.

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Thomson Model

All matter is made of atoms and all the atoms are electrically neutral. Having discovered electron as a constituent of atom, Thomson concluded that there must be an equal amount of positive charge present in an atom. On this basis he proposed a model for the structure of atom.

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Discovery of Proton

Much before the discovery of electron, Eugen Goldstein (in 1886) performed an experiment using a perforated cathode (a cathode having holes in it) in the discharge tube filled with air at a very low pressure. When a high voltage was applied across the electrodes in the discharge tube, a faint red glow was observed behind the perforated cathode.

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Discovery of Electron

Dalton's atomic theory, proposed in the year 1803, considered the atom to be the smallest indivisible constituent of all matter. The Dalton's theory could explain the law of conservation of mass, law of constant composition and law of multiple proportions known at that time.

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Atomic Structure

In 1803, Dalton’s atomic theory considered the atom to be the smallest indivisible constituent of all matter. The Dalton’s theory could explain the law of conservation of mass, law of constant composition and law of multiple proportions known at that time.

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Chemical Reactions and Equations

A substance which undergoes a chemical change is called the reactant and the substance which is formed as a result of a chemical change is called the product.

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Atoms and Molecules

An ancient Greek philosopher Democritus (460 - 370 BC) and Leucippus suggested that if we go on dividing matter, a stage will come when further division of particles will not be possible. Democritus called these individual particles 'atoms' (which means indivisible).

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Matter

Matter is any thing which has mass and occupies space. All solids, liquids and gases around us are made of matter. Atoms is a basic unit of  matter and all chemical properties of matter can be explained on its basis.

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Measurement in Science and Technology

Measurement is a process of comparing a physical quantity with a standard quantity. The standard quantity used to compare a physical quantity for its measurement is called unit.

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Effect of Redox Reactions: Corrosion & Rancidity

Rancidity is important in view of its direct link with foods and edibles. Both, corrosion and rancidity, are results of redox reactions.

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Oxidation and Reduction Reactions

When a substance gains oxygen during a reaction, it is said to be oxidized and when a substance loses oxygen during a reaction, it is said to be reduced. During the reaction process, one reactant gets oxidized while the other gets reduced. Such reactions are called oxidation reduction reaction or Redox Reactions.

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Double Displacement Reactions

Reactions in which there is an exchange of ions between the reactants, are called double displacement reactions.

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Displacement Reaction

The displacement reaction is one in which one element displaces another element from its compounds.

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Decomposition Reactions

A decomposition reaction is the one in which a compound decomposes into two or more than two substances (elements or compounds).

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Water Pollution

Water pollution is the contamination of water bodies like lakes, rivers, ground water and oceans. It occurs due to the discharge of untreated pollutants into water bodies. It not only affects plants and organisms living near the location of discharge but also travels to other locations through transportation of polluted water.

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Density of Water

Water behaves in an unusual way when it is heated from 0°C. As the temperature rises from 0°C to 4°C it actually contracts. However, from 4°C upwards it expands like any other liquid.

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Capillarity - Rise of Water

When a capillary tube with a fine bore is dipped in water, water rises in the capillary. The extent to which water rises depends on the diameter of the capillary. The smaller the diameter of the capillary, the higher will be the rise of water in the capillary tube.

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Surface Tension

Surface tension is the property of all the liquids. Due to this tension water drops try to occupy a minimum surface area.

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Polar Nature of Water

Water is a very effective solvent for ionic compounds. Although water is an electrically neutral molecule, it has a small positive charge (on the H atoms) and a negative charge (on the O atom).

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Hard Water and Soft Water

Water forms lather with soap which is used for cleaning purposes. It is called soft water. Sometimes water from some sources like rivers or hand pumps does not produce any lather with soap. It is called hard water.

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Water as Universal Solvent

Water is one of the best and most useful solvents. Water has a unique property of dissolving a large number of substances starting from solids such as common salt, sugar, to gases like oxygen, carbon dioxide.

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Purification of Water

Contaminated or non-potable water can be treated to turn it into potable or drinking water.

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Potable and Non-potable water

Potable water means water which is fit for drinking by humans and other animals. It can be consumed with low risk of immediate or long term harm.

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Sources of Water

Water is the most important substance needed for survival of living beings. Living beings cannot live long without water. Water is available in plenty on the earth.

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Genetic Engineering

Genetic Engineering is also called recombinant DNA technique. In this technique, gene from an organism of a species can be transferred to become part of the or genome of an organism belonging to another species which is then termed GMO genetically modified organism.

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Hereditary Disorders

Genes control all features of an organism. Some times a gene may change or mutate either in the gamete or zygote. Mutated gene may not remain normal. Also, sometimes a defective gene present in the parent may not be expressed in the parent as the dominant normal member of its pair may mask the effect of the defective gene.

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Sex Determination in Humans

The combination of sex chromosomes with autosomes determines whether the foetus will be a boy or a girl. The foetus develops from the zygote which is formed by the fusion of the two gametes, the male gamete or sperm and the female gamete or egg. Gametes are haploid while the zygote is diploid.

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Blood Group Inheritance in Humans

Every one is born with genes inherited from our parents. The blood group depends on the combination of a pair of genes, one of which is inherited from each parent.

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DNA Molecule

A DNA molecule is a polynucleotide (poly means many). It is made of units called nucleotides, each of which contains a nitrogenous base, a deoxy ribose sugar, and a phosphate.

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Genes

Genes Genes are present on chromosomes. The Genes are the "Mendelian factors" present in pairs (one received from the father, other from the mother), on the chromosomes. Thus, one member of a pair of genes present on the chromosomes has its pair on the homologous chromosome at the same location.

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Chromosomes

Genes are responsible for heredity. They are present on chromosomes at fix points.

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Mendel's Laws of Inheritance

The question about heredity intrigued many scientists. Gregor Johann Mendel (1822 -1884), an Austrian monk undertook the laborious task of finding the answers. He selected some pea plants, grew them year after year, compiled a lot of data, analysed and postulated certain laws of inheritance for the first time.

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Introduction to Heredity and Variation

All organisms resemble, in structure, to their parents. The passing down of similar characters generation after generation is termed heredity. Heredity is controlled by genes. Differences in gene combinations lead to variations or differences even among members of the same family. The science of heredity and variation is termed Genetics.

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Combination Reactions

In combination reactions, two or more substances (elements or compounds) simply combine to form a new substance.

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Balanced Chemical Equations

According to the law of conservation of mass, matter can neither be created nor destroyed. Thus, mass of each element present in the products of a chemical reaction must be equal to its mass present in the reactants.

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