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Periodic Classification of Elements    
  • The grouping of elements with similar properties together and the separation of elements with dissimilar properties is known as classification of elements. The table, which classification of elements on the basis of their properties, is called the periodic table. Dobereiner grouped the elements into triads and Newlands gave the Law of Octaves. Mendeleev arranged the elements in increasing order of their atomic masses and according to their chemical properties.
 
  • Dobereiner’s Triads arranged elements in an increasing order of atomic mass, in groups of three. The atomic mass of the middle element was the arithmetic mean of the other two elements of the triad.
 
  • Newland’s law of octaves states that on arranging elements in increasing order of their atomic mass, the eight element resembles the first in physical and chemical properties, just like the eight node on a musical scale resembles the first note.
 
  • According to Mendeleev’s periodic law, the physical and chemical properties of elements are periodic functions of their atomic mass. Mendeleev corrected the atomic masses of a few elements on the basis of their positions in the periodic table. Mendeleev even predicted the existence of some yet to be discovered elements on the basis of gaps in his Periodic Table.
 
  • Mendeleev’s Periodic Table contains vertical columns called ‘group’ and horizontal rows called ‘periods’. While developing the Periodic Table, there were a few instances where Mendeleev had to place an element with a slightly greater atomic mass before an element with a slightly lower atomic mass. The sequence was inverted so that elements with similar was inverted so that elements with similar properties could be grouped together. Mendeleev’s table could not assign a proper position to hydrogen or to the lanthanides and actinides and isotopes. Isotopes of all elements posed a challenge to Mendeleev’s Periodic Law. Another problem was that the atomic masses do not increase in a regular manner in going from one element to the next. So it was not possible to predict how many elements could be discovered between two elements - especially when we consider the heavier elements.
 
  • In 1913, Henry Moseley showed that the atomic number of an element is a more fundamental property than its atomic mass. Accordingly, Mendeleev’s Periodic Law was modified and atomic number was adopted as the basis of Modern Periodic Table and the Modern Periodic Law.
 
  • The vertical columns are called groups, while the horizontal rows are called periods. The noble gases are on the extreme right of the table and on the table’s extreme left, are the alkali metals. Transition elements are placed in the B subgroups in the middle of the table. The inner transition elements lanthanides and actinides, are placed in two separate series at the bottom of the periodic table. Group number more...

Organic Chemistry     Organic chemistry is that branch of chemistry which deals with the study of compounds of carbon with hydrogen (hydrocarbons), and their derivatives. Presently about five million organic compound are known. Organic compounds were found to contain mainly hydrogen and carbon. Therefore, organic chemistry is defined as the study of hydrocarbons and their derivatives. Most atoms are only capable of forming small molecules. However one or two can form larger molecules. By far and away the best atom for making large molecules with is Carbon. Carbon can make molecules that have tens, hundreds, thousands even millions of atoms! The huge number of possible combinations means that there are more Carbon compounds that those of all the other elements put together! A single Carbon atom is capable of combining with up to four other atoms. We say it has a valency of 4. Sometimes a Carbon atom will combine with few that will combine with itself. In other words Carbon combines with other Carbon atoms. This means that Carbon atoms can form chains and rings onto which other atoms can be attached. This leads to a huge number of different compounds. Organic Chemistry is essentially the chemistry of Carbon. Carbon compounds are classified according to how the Carbon atoms are arranged and what other groups of atoms are attached.   Hydrocarbons: The simplest Organic compounds are made up of only Carbon and Hydrogen atoms only. Even these run into thousands! Compounds of Carbon and Hydrogen only are called Hydrocarbons.  
  • Alkanes: In the alkanes, all four of the Carbon valency bonds are taken up with links to different atoms. These types of bonds are called single bonds and are generally stable and resistant to attack by other chemicals. Alkanes contain the maximum number of Hydrogen atoms possible. They are said to be saturated. The simplest Hydrocarbon is:
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    • Methane: \[C{{H}_{4}}\]this is the simplest member of a series of hydrocarbons. Each successive member of the series has one more Carbon atom than the preceding member.
    • Ethane: \[{{C}_{2}}{{H}_{6}}.\]
    • Propane-(heating fuel): \[{{C}_{3}}{{H}_{8}}.\]
    • Butane - (lighter / camping fuel): \[{{C}_{4}}{{H}_{10}}.\]
    • Pentane: \[{{C}_{5}}{{H}_{12}}.\]
    • Hexane: \[{{C}_{6}}{{H}_{14}}.\]
      Polythene is a very large alkane with millions of atoms in a single molecule. Apart from being flammable, alkanes are stable compounds found underground.  
  • Alkenes: Another series of compounds is called the alkenes. These have a general formula: CnH2n. These compounds are named in a similar manner to the alkanes expect that the suffix is -end. Alkenes have fewer hydrogen atoms than the alkanes. The extra valencies left over occur as double bonds between a pair of Carbon atoms. The double bonds are more reactive than single bonds making the alkenes chemically more reactive. The simplest alkenes are listed in the table below:
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    • Ethane (used as an industrial starter chemical): \[{{C}_{3}}{{H}_{4}}.\]
    • Propene: \[{{C}_{4}}{{H}_{6}}.\]
    • Butane: \[{{C}_{4}}{{H}_{8}}.\]
    • Pentene: \[{{C}_{5}}{{H}_{10}}.\]
    • Hexane: C6H12.
     
  • Alkynes: A third series are the alkynes. These have the following formula: \[Cn{{H}_{2}}n-2.\]These more...

  • Matter and Its Nature     A. Matter and its Nature
    • Anything that possesses mass, occupies space, offers resistance and can be perceived through one or more of our sense is called matter.
     
    • Matter is made up of particles. Particles of matter have space between them and are continuously moving and attract each other.
     
    • Matter can exist in three states-
  • Solid
  • Liquid
  • Gas.
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    • Solid has a definite shape, distinct boundaries and fixed volumes, Solids have a tendency to maintain their shape when subjected to outside force. Solids may break under force but it is difficult to change their shape, so they are rigid.
     
    • Liquids have no fixed shape but have a fixed volume. They take up the shape of the container in which they are kept. Liquids flow and change shape, so they are not rigid but can be called fluid.
     
    • A gas has no definite volume or shape. Gases are highly compressible as compared to solids and liquids. The liquefied petroleum gas (LPG) cylinder that we get in our home for cooking or the oxygen supplied to hospitals in cylinders is compressed gas. Compressed nature gas (CNG) is used as fuel these days in vehicles.
     
    • The forces of attraction between the particles (inter-molecular force) are maximum in solids, intermediate in liquids and minimum in solids, intermediate in liquids and minimum in gases. The spaces in between the constituent particles and kinetic energy of the particles are minimum in the case of solids, intermediate in liquids and maximum in gases.
     
    • The arrangement of particles is most ordered in the case of solids, in the case of liquids layers of particles can slip and slide over each other while for gases, there is no order, particles just move about randomly.
     
    • In spite of above differences all kinds of matter have a common property, the property of having a mass.
     
    • The states of matter are inter-convertible. The state of matter can be changed by changing temperature or pressure.
     
    • On increasing the temperature of solids, the kinetic energy of the particles increases. Due to the increase in kinetic energy, the particle start vibrating with greater speed. The energy supplied by heat overcomes the forces of attraction between the particles. The particles leave their fixed positions and start moving more freely. A stage is reached when the solid melts and is converted to a liquid. The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.
     
    • The process of melting, that is, change of solid state into liquid state is also known as fusion.
     

    The Reproductive System     Asexual reproduction                         
    • Asexual reproduction allows an organism to rapidly produce many offspring without the time and resources committed to courtship, finding a mate, and mating.
     
    • Fission, budding, fragmentation, and the formation of rhizomes and stolon’s are some of the mechanisms that allow organisms to reproduce asexually.
     
    • The hydra produces buds;
     
    • Starfish can regenerate an entire body from a fragment of the original body.
     
    • The lack of genetic variability in asexuality reproducing populations can be detrimental when environmental conditions change quickly.
      Sexual Reproduction
    • In sexual reproduction new individuals are produced by the fusion of haploid gametes to form a diploid zygote.
     
    • Sperm are male gametes, ova (ovum singular) are female gametes.
     
    • Meiosis produces cells that are genetically distinct from each other.
     
    • Fertilization is the fusion of two such distinctive cells.
     
    • Rotifers will reproduce asexually when conditions are favorable by having females produce eggs by mitosis. When conditions deteriorate, rotifers will reproduce sexually and encase their zygotes inside a resistant shell. Once conditions improve, these eggs hatch into diploid individuals. Rotifers thus use sexual reproduction as way to survive a deteriorating environment.
     
    • Sexual reproduction offers the benefit of generating genetic variation among offspring, which enhances the chances of the population’s survival.
     
    • Costs of this process include the need for two individuals to mate, courtship rituals, as well as a number of basic mechanisms described later.
      Human Reproduction and Development
    • Human reproduction employs internal fertilization, and depends on the integrated action of hormones, the nervous system, and the reproductive system
     
    • Gonads are sex organs that produce gametes. Male gonads are the testes, which produce sperm and male sex hormones. Female gonads are the ovaries, which produce eggs (ova) and female sex hormones.
      The Male Reproductive System
    • Testes are suspended outside the abdominal cavity by the scrotum, a pouch of skin that keeps the testes close or far from the body at an optimal temperature for sperm development.
     
    • Seminiferous tubules are inside each testis, and are where sperm are produced by meiosis. About 250 meters (850 fe.et) of tubules are packed into each testis.
     
    • Spermatocytes inside the tubules divide by meiosis to produce spermatids that in turn develop into mature sperm.
     
    • Sperm production begins at puberty and continues throughout life, with several hundred million sperm being produced each day. Once sperm form they move into the epididymis, where they mature more...

    The Respiratory System     Respiration in Single Cell Animals Single-celled organisms exchange gasses directly across their cell membrane. However, the slow diffusion rate of oxygen relative to carbon dioxide limits the size of single celled organisms. Simple animals that lack specialized exchange surfaces have flattened, tubular, or thin shaped body plans, which are the most efficient for gas exchange. However these simple animals are rather small in size.   Respiration in multicellular animals Large animals cannot maintain gas exchange by diffusion across their outer surface. They developed a variety of respiratory surfaces that all increase the surface area for exchange, thus allowing for larger bodies. A respiratory surface is covered with thin, moist epithelial cells that allow oxygen and carbon dioxide to exchange. Those gases can only cross cell membranes when they are dissolved in water or an aqueous solution, thus respiratory surfaces must be moist.   Respiratory System Principles 1. Movement of an oxygen containing medium so it contacts a moist membrane overlying blood vessels.                                2. Diffusion of oxygen from the medium into the blood.   3. Transport of oxygen to the tissues and cells of the body.   4. Diffusion of oxygen from the blood into cells.   5. Carbon dioxide follows a reverse path.

    The Circulatory System     Circulatory Systems in Single-celled Organisms Single-celled organisms use their cell surface as a point of exchange with the outside environment.   Sponges are the simplest animals, yet even they have a transport system. Seawater is the medium of transport and is propelled in and out of the sponge by biliary action.   Simple animals, such as the hydra and planarian lack specialized organs such as hearts and blood vessels, instead using their skin as an exchange point for materials. This, however, limits the size an animals can attain. To become larger, they need specialized organs and organ systems.   Circulatory Systems in Multicellular Organisms Multicellular animals do not have most of their cells in contact with the external environment and so have developed circulatory systems to transport nutrients, oxygen, carbon dioxide and metabolic wastes. Components of the circulatory system include            i. Blood: a connective tissue of liquid plasma and cells ii. Heart: a muscular pump to move the blood iii. Blood vessels: arteries, capillaries and veins that deliver blood to all tissues   Vertebrate Cardiovascular System The vertebrate cardiovascular system includes a heart, which is a muscular pump that contracts to propel blood out to the body through arteries, and a series of blood vessels.   The upper chamber of the heart, the atrium (pl. atria), is where the blood enters the heart. Passing through a valve, blood enters the lower chamber, the ventricle.   Contraction of the ventricle forces blood from the heart through an artery.   The heart muscles is composed of cardiac muscle cells.   Arteries are blood vessels that carry blood away from heart. Arterial walls are able to expand and contract. Arteries have three layers of thick walls. Smooth muscles fibers contract, another layer of connective tissue is quite elastic, allowing the arteries to carry blood under high pressure.   The aorta is the main artery leaving the heart.   The pulmonary artery is the only artery that carries oxygen-poor blood. The pulmonary artery carries deoxygenated blood to the lungs. In the lungs, gas exchange occurs, carbon dioxide diffuses out, oxygen diffuses in   Arterioles are small arteries that connect larger arteries with capillaries. Small arterioles branch into collections of capillaries known as capillary beds. Capillaries, are thin-walled blood vessels in which gas exchange occurs. In the capillary, the wall is only one cell layer thick. Capillaries are concentrated into capillary beds. Some capillaries have small pores between the cells of the capillary wall, allowing materials to flow in and out of capillaries as well as the passage of white blood cells.   Changes in blood pressure also occur in the various vessels of the circulatory system. Nutrients, wastes, and hormones are exchanged across the thin walls of capillaries. Capillaries are microscopic in size, although blushing is one manifestation of blood flow into capillaries. Control of blood flow into capillary beds is done by nerve-controlled sphincters.   The circulatory system functions in the delivery of more...

    Acid, Base and Salts     1.  Acid
    • Then word ‘acid’ is derived from a Latin word, which means “sour”. The sour taste of most of the fruits and vegetables is due to various types of acids present in them. The digestive fluids of most of the animals and humans also contain acids.
     
    • An acid is a compound, which on dissolving in water yields hydronium ions as the only positive ions. The characteristic property of an acid is due to the presence of these hydronium ions.
     
    • Acids are compounds that contain Hydrogen (Hydrochloric, HCl; Sulphuric, Nitric, However, not all compounds that contain Hydrogen are acids (Water, Methane, Acids are usually compounds of nonmetals with Hydrogen and sometimes Oxygen.
     
    • Acids can be classified in various ways, depending on the factors mentioned below:
     
  • Classification Based on the Strength of the acid.
  •  
  • Classification Based on the Basicity of the Acid.
  •  
  • Classification Based on the concentration of the acid.
  •  
  • Classification Based on the presence of Oxygen.
  •  
    • The strength of an acid depends on the concentration of the hydronium ions present in a solution. Greater the number of hydronium ions present, greater is the strength of acid. However, some acids do not dissociate to any appreciable extent in water such as carbonic acid. Therefore, these acids will have a low concentration of hydronium ions.
     
    • Strong Acid: An acid, which dissociates completely or almost completely in water, is classified as a strong acid. It must be noted that in these acids all the hydrogen ions (H+) combine with water molecule and exist as hydronium ions Examples of strong acids are: hydrochloric acid, sulphuric acid, nitric acid etc.
     
    • Weak Acid: An acid that dissociates only partially when dissolved in water, is classified as a weak acid. Most of the molecules remain in solution in molecular from itself in such acid. Examples are: acetic acid, formic acid, carbonic acid etc.
     
    • Acids are generally sour in taste. Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators. The indicators change their colour when added to a solution containing an acidic or a basic substance. Turmeric, litmus, china rose petals (Gudhal), etc., are some of the naturally occurring indicators.
     
    • The most commonly used natural indicator is litmus. It is extracted from lichens. It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper known as litmus paper. Generally, it is available as red and blue litmus paper.
     

    Properties of Gases    
  • Properties of Gases
    • First, we know that a gas has no definite volume or shape; a gas will fill whatever volume is available to it. Contrast this to the behavior of a liquid, which always has a distinct upper surface when its volume is less than that of the space it occupies.
     
    • The other outstanding characteristic or gases is their low densities, compared with those of liquids and solids. The most remarkable property of gases, however, is that to a very good approximation, they all behave the same way in response to changes in temperature and pressure, expanding or contracting by predictable amounts. This is very different from the behavior of liquids or solids, in which the properties of each particular substance must be determined individually.
     
    • All gases expand equally due to equally due to equal temperature difference.
     
    • Diffusion of gases: The phenomenon in which a substance mixes with another because of molecular motion, even against gravity- is called diffusion.
     
    • The pressure of a gas: The molecules of a gas, being in continuous motion, frequently strike the inner walls of their container. As they do so, they immediately bounce off without loss of kinetic energy, but the reversal of direction (acceleration) imparts a force to the container walls. This force, divided by the total surface area on which it acts, is the pressure of the gas.
     
    • The unit of pressure in the SI system is the pascal (Pa), defined as a force of one newton per square meter (1 Nm-2 = 1kg m-1 s-2.)
     
    • Temperature and Temperature Scale: Temperature is defined as the measure of average heat. Temperature is independent of the number of particles or size and shape of the object. The water boiling temperature is same for all types of containers.
     
    • Thermometer: The device which is used to define the measure of temperature of an object is Thermometer.
     
    • Temperature scale: A reference scale with respect to which the temperatures can be measured is known as ‘scale of temperature’ Various scales of temperatures are in use. Important scales of temperature are:
      (i) Celsius scale (ii) Kelvin scale (iii) Fahrenheit scale (iv) To devise a scale of temperature, fixed reference points (temperature) are required, with respect to which all other temperatures are measured. For both Celsius and Fahrenheit Scales of temperatures, the fixed points are as follows  
    • Lower fixed point: Melting point of pure ice at normal atmospheric pressure is regarded as the lower fixed point.
     
    • Upper fixed point: Boiling point of pure water at normal atmospheric pressure is regarded as the lower fixed point.
     
    • Celsius scale: In this scale the more...

    Atomic Structure    
    • An atom is the smallest particle of the element that can exist independently and retain all its chemical properties. Atoms are made up of fundamental particles: electrons, protons and neutrons.
     
    • Dalton’s Atomic Theory: John Dalton provided a simple theory of matter to provide theoretical justification to the laws of chemical combinations in 1805. The basic postulates of the theory are:
     
    • All substances are made up of tiny, indivisible particles called atoms.
     
    • Atoms of the same elements are identical in shape, size, mass and other properties.
     
    • Each elements is composed of its own kind of atoms. Atoms of different elements are different in all respects.
     
    • Atom is the smallest unit that takes part in chemical combinations.
     
    • Atoms combine with each other in simple whole number ratios to form compound atoms called molecules.
     
    • Atoms cannot be created, divided or destroyed during any chemical or physical change.
     
    • Representation of an Atom by a Symbol: Dalton was the first scientist to use the symbols for elements in a very specific sense. When he used a symbol for an element he also meant a definite quantity of that element, that is, one atom of that element. A symbol signifies a shorthand representation of an atom of an element. The symbol of any element is based the English name or Latin name (written in English alphabets) and many of the symbols are the first one or two letters of the element’s name in English. The first letter of a symbol is always written as a capital letter (uppercase) and the second letter as a small letter (lowercase). Examples are: (i) hydrogen- H (ii) aluminium- Al and not AL (iii) cobalt- Co and not CO. Symbols of some elements are formed from the first letter of the name and a letter, appearing later in the name. Examples are (i) chlorine, Cl, (ii) zinc, Zn etc.
     
    • Other symbols have been taken from the names of elements in Latin, German or Greek. For example, the symbol of iron is Fe from its Latin name ferrum, sodium is Na form natrium, potassium is K from kalium. Therefore, each element has a name and a unique chemical symbol.
     
    • Size of the Atom / Elements: Atoms are very small, they are smaller than anything that we can imagine or compare with. One hydrogen atom, the smallest atom known, is approximately mm in diameter. Atomic radius is measured in nanometers. 1 m = 109 nm.
     
    • Atomic Mass: The mass of a particular atom is taken as a standard unit and the masses of other atoms are related to this standard. Hydrogen being the lightest element and being more...

    Chemical Bonding    
    • Atoms are made up of three smaller particles called protons, neutrons and electrons. The protons and neutrons are found in the nucleus of the atom. Protons have a single positive charge. This is called the Atomic Number of an atom. The Atomic Number tells us the number of electrons that the atom contains. It is these electrons that determine the chemical properties of the atom and the way it combines with other atoms to form specific compounds. Electrons have a single negative charge. Normally, atoms are electrically neutral so that the number of electrons is equal to the number of protons.
     
    • Electrons orbit around the nucleus. Electrons cannot orbit the nucleus of an atom in any orbit. The electrons are restricted to specific paths called orbitals or shells. Each shell can only hold a certain number of electrons. When a shell is full, no more electrons can go into that shell. The key to the properties of atom is the electrons in the outer shell. A complete outer shell of electrons is a very stable condition for an atom.
     
    • Valency: Hydrogen is the simplest element. It has one electron. Its outer shell only holds two electrons. Valency can be simply defined as the number of Hydrogen atoms that an element can combine with. The atoms with full electron shells (Helium, Neon, Argon) are chemically inert forming few compounds. The atoms don’t even interact with each other very much. These elements are gases with very low boiling points. The atoms with a single outer electron or a single missing electron are all highly reactive. Sodium is more reactive than Magnesium. Chlorine is more reactive than Oxygen Generally speaking, the closer an atoms is to having a full electron shell, the more reactive it is. Atoms with one outer electron are more reactive than those with two outer electrons, etc. Atoms that are one electron short of a full shell are more reactive than those that are two short.
     
    • Chemical bonds are what hold atoms together to form the more complicated aggregates that we know as molecules and extended solids. The forces that hold bonded atoms together are basically just the same kinds of electrostatic attractions that bind the electrons of an atom to its positively-charged nucleus. Chemical bonding occurs when one or more electrons are simultaneously attracted to two nuclei
     
    • Mainly 3 Types of bonds can be present in Chemical Compounds.
     
  • Electrovalent or lonic Bond: It is formed by Transferring of Electrons between 2. Atoms. These types of bonds are mainly formed between Metals and Non - Metals. These compounds exist in solid form. These compounds have high boiling Point. Melting Point and thermal stability.
  •  
  • Covalent Bond: It is formed by equal sharing of Electrons between 2 Atoms. This type of bond is mainly formed between non more...



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