Chemistry - Introduction

• Chemistry is a branch of Natural Science that studies about the structure, composition, and changing properties of matters.
• Chemistry studies the smallest part of a matter i.e. atom (along with its all properties) to the large materials (e.g. gold, silver, iron, etc.) and their properties.
• Chemistry also studies the intermolecular forces (that provide matter the general properties) and the interactions between substances through the chemical reactions.
• In 1998, Professor Raymond Chang defined Chemistry as −
• "Chemistry" to mean the study of matter and the changes it undergoes.
• It is believed that the study of chemistry started with the theory of four elements propounded by Aristotle.
• The four theory of elements states that “fire, air, earth, and water were the fundamental elements from which everything is formed as combination.”
• Because of his classical work namely “The Sceptical Chymist,” Robert Boyle, is known as the founding father of chemistry.
• Boyle formulated a law, became popular as ‘Boyle’s Law.’
• Boyle’s law is an experimental gas law that analyzes the relationship between the pressure of a gas and volume of the respective container.
• By advocating his law, Boyle rejected the classical ‘four elements’ theory.
• The American scientists Linus Pauling and Gilbert N. Lewis collectively propounded the electronic theory of chemical bonds and molecular orbitals.
• The United Nations declared 2011 as the ‘International Year of Chemistry.’
• The matter is defined in chemistry as anything that has rest mass and volume and also takes space.
• The matter is made up of particles.
• The atom is the fundamental unit of chemistry.
• The atom consists of a dense core known as the atomic nucleus and it is surrounded by a space known as the electron cloud.
• The nucleus (of an atom) is composed of protons (+ve charged particles) and neutrons (neutral or uncharged particles); collectively, these two are known as nucleons (as shown in the image given below).
• A chemical element is a pure form of a substance; it consists of single type of atom.
• The periodic table is the standardized representation of all the available chemical elements.
• A compound is a pure form of a substance; it composed of more than one elements.

Radioactivity

• The process of emission of particles from nuclei because of the nuclear instability; is known as radioactivity.
• The substance that releases such energy/rays is known as radioactive substance.
• The invisible rays released from such radioactive substance are known as radioactive rays.
• Likewise, radioactivity is a nuclear phenomenon that happens (naturally) because of the nuclear instability of atoms.
• In 1896 Henri Becquerel first observed the phenomena of radioactivity, but the term ‘radioactivity’ was coined by Marie Curie.
• Marie Curie discovered the radioactive elements namely Polonium and Radium in 1898.
• For her discovery, Marie Curie won the Nobel Prize.

Radioactive Rays

• After long years of experiment, Ernest Rutherford along with his colleague (Hans Geiger and his student Ernest Marsden), discovered alpha rays, beta rays, and gamma rays.

• These rays emitted as the result of the disintegration of atoms.

Alpha (α) Particles

• Alpha particles are usually composed of two protons and two neutrons, which are tightly bound together.
• Alpha particles are being released during radioactive decay (or alpha decay) from the nucleus radio nuclides.
• The alpha particles are identical to the nucleus of either normal helium atom or doubly ionized helium atom.
• In comparison to other particles (i.e. Gamma and Beta), alpha particles are heavy and slow. Therefore, alpha particles have very small range in the air.
• Because of slow speed, Alpha particles have very weak penetrating powers; these particles are even stopped by a thin paper sheet (see image given above).
• Because of having the double positive charge, alpha particles are highly ionizing.

Beta (β) Particles

• Beta particles are the fast moving electrons emitted by some radio nuclides during the radioactive decay (also known as beta decay).
• Beta particles are of much lighter weight and carry a single negative charge.
• Beta particles are rarely ionizing than the alpha particles.
• Because of having lighter weight, beta particles can travel much farther than alpha particles; however, beta particles can be stopped by several sheet of papers or one sheet of aluminum.
• Beta particles are negatively charged and get attracted towards positively charged particles.

Gamma (?) Particles

• Gamma particles are the bundle of high energy namely electromagnetic energy (photon) emitted by the radioactive elements during the radioactive decay.
• Among all three particles (alpha, beta, and gamma), gamma particles are the most energetic photons.
• Gamma particles, which are the form of electromagnetic radiation(EMR), originate from the nucleus.
• The wavelengths of gamma are the shortest among all three.
• Gamma particles have no charge and they are neutral; therefore, they are unaffected by magnetic and electric fields.

Uses of Radioactive Elements

Radioactive elements are used in −

• Medical field (treatment of many diseases)
• Industrial process
• Energy production – Nuclear reactors

Nuclear Energy

• Nuclear reactions release tremendous amount of energy (known as nuclear energy), which are being used to produce electricity in a nuclear power plant.
• The nuclear energy normally produced by nuclear fission, nuclear fusion, and nuclear decay.
• In 1938, German chemists Otto Hahn, Fritz Strassmann, and the Austrian physicist Lise Meitner conducted the experiments in which the products of neutron-bombarded uranium. As result of this experiment, the relatively tiny neutron split the nucleus of the massive uranium atoms into two roughly equal pieces and released massive energy.
• The nuclear experiments of Otto Hahn and his colleagues are popular as nuclear fission.

Nuclear Fission

• The process of nuclear fission produces free neutrons and gamma photons, while doing this also releases a very large amount of energy.
• Nuclear fission is an exothermic reaction, which can release large amounts of energy in the forms of electromagnetic radiation as well as kinetic energy.
• Nuclear fission, sometimes, can occur naturally (i.e. without neutron bombardment) as a type of radioactive decay.

Types of Nuclear Fission

Following are the major types of Nuclear Fission −

• Chain Reaction and
• Fission Reaction

Chain Reaction

• When one single nuclear reaction causes one or more subsequent nuclear reactions, it is known as chain reaction.
• Such chain reaction increases the possibility of a self-propagating series of nuclear reactions.
• The nuclear chain reactions release million times more energy per reaction than any other chemical reaction; therefore, it is also known as explosive or uncontrolled chain reaction.
• When a heavy atom experiences nuclear fission, it normally breaks into two or more fission fragments. During the process, several free neutrons, gamma rays, and neutrinos are emitted, and ultimately a large amount of energy is released.
• Following are the two examples of chain reaction −

  --> 35U + → neutron Fission fragments + 2.4 neutrons + 192.9 MeV

  --> 235Pu + → neutron Fission fragments + 2.9 neutrons + 198.9 MeV

• In atom bomb, chain reaction technology is used, as it required consistent source of energy.

Fission Reactions

• The fission reaction in which neutrons (produced by fission of fuel atoms) are used to induce yet more fission for the release of sustainable energy, is known as fission reactions.
• Such reactions are slow and controllable; therefore, also known as controlled chain reaction.
• The power (electricity) producing nuclear reactor is an ideal example of controlled chain reaction.
• Based on the properties and type of usages, fission/controlled chain reaction is classified as −

  --> Power reactors

  --> Research reactors

  --> Breeder reactors

• These power reactors generally convert the kinetic energy of fission products into heat; further, the heat is used to heat a working fluid that drives a heat engine, which ultimately generates mechanical or electrical power.

Basic components of Nuclear Reactor

Following are the essential components of a nuclear reactor −

• Nuclear fuels − Such as Uranium (233U, 235U), thorium (Th232), plutonium (Pu239).
• Moderators − Used to control the emitted neutrons. E.g. heavy water, beryllium, graphite, etc.
• Coolant − It is used to cool the reactor. E.g. water, steam, helium, CO2, air, molten metals, etc.
• Control rods − It is used to run and stop the fission reaction. E.g. cadmium or boron rods are used for such purpose.

Nuclear Fusion

• The process by which two light nuclei are fused to form a heavy nucleus is known as nuclear fusion; during this process, a tremendous amount of energy is being released known as nuclear energy.
• The best example of nuclear fusion is – hydrogen bomb.
• A hydrogen bomb is about 1,000 times more powerful than an atom bomb.

Metals and Alloys

• The material (which could be an element, compound, or alloy) that is characteristically hard, shiny, opaque, and has the property to conduct heat and electricity, is known as metal.
• Metals are naturally found in the earth’s crust in impure form i.e. ores. And, it is extracted through mining process.
• Among all known 118 elements (of the periodic table), about 91 elements are metals.

Features of Metals

Following are the significant features of metals −

• Metals are generally malleable - it means, its shape can be changed permanently without breaking and cracking.
• Metals are fusible – it means; it can be fused or melted easily.
• Metals are ductile – it means; it can be given any shape even a thin sheet or wire.
• Metals are good conductor of heat and electricity; heaver, lead is an exception, as it does not carry electricity.
• Metals naturally react with various non-metals and forms compounds. Metals can react with bases and acids. E.g. 4 Na + O2 → 2 Na2O (sodium oxide), etc.

Alloys

• An alloy is a product of the mixture of two or more elements in which metal dominates.
• In order to produce or manufacture a desirable product, different metals (in different ratios) are mixed (i.e. alloys). E.g. alloys of iron namely stainless steel, cast iron, alloy sheet, etc. contribute a large proportion of both by quantity and commercial value.
• Metals are usually made alloys with the purpose to make it more resistant to corrosion, less brittle, to give attractive colors, etc.

Metal Terminologies

• Base Metal − In chemistry, the meaning of base metal is – the metal that can be easily oxidized or corroded as well as reacts easily with HCl (dilute hydrochloric acid) and forms hydrogen. E.g. iron, nickel, zinc, lead, etc.
• Ferrous Metal − "Ferrous" is a Latin word, which means the substance "containing iron." E.g. steel, etc.
• Heavy Metal − The metal which are much denser than the normal metal is categorized as heavy metal. The heavy metals are toxic or poisonous at low concentrations. E.g. mercury (Hg), arsenic (As), chromium (Cr), cadmium (Cd), thallium (Tl), and lead (Pb).
• Precious Metal − The metallic elements, which have rare metallic chemical element of high economic value, is categorized as precious metal. E.g. platinum, gold, silver, palladium, etc.
• Noble Metal − The metals that are resistant to corrosion or oxidation. E.g. ruthenium (Ru), rhodium (Rh), palladium (Pd), etc.

Application of Metals

Following are the significant applications of the metals −

• As metals are good conductor of heat and electricity; therefore, it is used as electric wire and in many other electric appliances including electric motors, etc. E.g. copper, silver, aluminum, etc.
• Heavy metals are being used in the constructions of bridge, pool, and for many such purposes.
• Many metals are used to manufacture various home items, such as, utensils, pots, stoves, etc.
• Metals are frequently used to manufacture many types of tools ranging from a simple screw driver to a heavy rod roller.
• Precious metals have beautiful look and they are attractive (e.g. gold, silver, etc.); therefore, they are used as ornaments.
• Some specific metal is used for heat sinks that protects the sensitive equipment from overheating.
• Radioactive metals (e.g. uranium and plutonium) are used in the generation of nuclear energy.
• Mercury is a metal that remains in liquid form at room temperature; it is used in thermometer.

Laws in Chemistry

• The laws of nature related to chemistry is known as chemical laws.
• Chemical reactions, normally, are administrated by certain laws, which are observed and formulated in words become fundamental concepts in chemistry.
• Following are the significant chemical laws − Laws Explanation Avogadro's Law “Equal volumes of all gases, at the same temperature and pressure, have the same number of molecules” Beer–Lambert law, (or simply Beer's law or Lambert–Beer law) “Explains the attenuation of light to the properties of the material through which it (light) passes” Boyle's Law “The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system” Charles' Law (also known as Law of Volume) “When the pressure on a sample of a dry gas is held constant, the Kelvin temperature and the volume will be directly related” Fick's Laws of Diffusion Describes “diffusion” (of flux) Gay-Lussac's Law "All gases have the same mean thermal expansivity at constant pressure over the same range of temperature" Le Chatelier's Principle ("The Equilibrium Law") “When any system at equilibrium is subjected to change in concentration, temperature, volume, or pressure, then the system readjusts itself to counteract (partially) the effect of the applied change and a new equilibrium is established” Henry's Law “The law calculates the concentration of gas in the solution under pressure” Hess's Law “The change of enthalpy in a chemical reaction (it means, the heat of reaction at constant pressure) is independent of the pathway between the initial and final states” Law of conservation of energy “Energy can neither be created nor be destroyed” Raoult's Law “The partial vapor pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its mole fraction in the mixture” Faraday's Law Electrolysis “The amount of substance produced at an electrode is directly proportional to the quantity of electricity passed” Atomic Theory “Matter is composed of distinct units known as atoms” Köhler Theory “Explains the process in which water vapor condenses and forms the liquid cloud drops” Van 't Hoff Equation “Describes change in the equilibrium constant of a chemical reaction” Transition State Theory “The reaction rates of elementary chemical reactions” Grotthuss–Draper Law “It describes that the light which is absorbed by a system/surface can bring a photochemical change” Kinetic Theory of Gases “Describes the behavior of a hypothetical ideal gas” Aufbau Principle “Explains that the electrons orbiting the atoms first fill the lowest energy levels and then second higher levels and so on and so forth” Hund's Rule “ Explains that every orbital in a sublevel is singly occupied before any orbital is doubly occupied” Collision Theory “Based on the kinetic theory of gases, collision theory describes that the gas-phase chemical reactions occur when molecules collide with sufficient kinetic energy”

Discovery of Elements

• Most likely copper was the first element, which was mined and used by humans.
• The evidence of earliest use of copper was found in Anatolia, which belongs to 6,000 BCE.
• The lead was most likely the second element that humans start using.
• The oldest known artifact of lead is statuette, which was found in a temple of Osiris, Abydos, Egypt.
• The statuette of Osiris temple belongs to (about) 3,800 BCE.
• The oldest known gold treasure was discovered in Varna, Necropolis (Bulgaria).
• This gold treasure belongs to (about) 4,400 BCE.
• Discovery of silver is almost same as of gold; its evidence was found in Asia Minor.
• Some evidence say that the iron was known from (about) 5,000 BCE.
• The oldest known iron objects, which was used by the humans, were found in Egypt (belongs to 4000 BCE).
• The following table illustrates the significant elements with their discovery date and discovers − Element Discoverer Discovery Date Copper Middle East (Place) About 9,000 BCE Lead Egypt (Place) About 7,000 BCE Gold Bulgaria (Place) About 6,000 BCE Silver Asia Minor (Place) About 5,000 BCE Iron Egypt (Place) About 5,000 BCE Tin   About 3,500 BCE Sulfur Chinese/India About 2,000 BCE Mercury Egypt 2,000 BCE Phosphorus H. Brand 1669 Cobalt G. Brandt 1735 Platinum A. de Ulloa 1748 Nickel F. Cronstedt 1751 Bismuth C.F. Geoffroy 1753 Magnesium J. Black 1755 Hydrogen H. Cavendish 1766 Oxygen W. Scheele 1771 Nitrogen D. Rutherford 1772 Barium W. Scheele 1772 Chlorine W. Scheele 1774 Manganese W. Scheele 1774 Molybdenum W. Scheele 1781 Tungsten W. Scheele 1781 Zirconium H. Klaproth 1789 Uranium H. Klaproth 1789 Titanium W. Gregor 1791 Chromium N. Vauquelin 1797 Beryllium N. Vauquelin 1798 Vanadium M. del Río 1801 Potassium H. Davy 1807 Sodium H. Davy 1807 Calcium H. Davy 1808 Boron L. Gay-Lussac and L.J. Thénard 1808 Fluorine A. M. Ampère 1810 Iodine B. Courtois 1811 Lithium A. Arfwedson 1817 Cadmium S. L Hermann, F. Stromeyer, and J.C.H. Roloff 1817 Selenium J. Berzelius and G. Gahn 1817 Silicon J. Berzelius 1823 Aluminium H.C.Ørsted 1825 Bromine J. Balard and C. Löwig 1825 Thorium J. Berzelius 1829 Lanthanum G. Mosander 1838 Rubidium R. Bunsen and G. R. Kirchhoff 1861 Thallium W. Crookes 1861 Indium F. Reich and T. Richter 1863 Helium P. Janssen and N. Lockyer 1868 Neon W. Ramsay and W. Travers 1898 Xenon W. Ramsay and W. Travers 1898 Fermium A. Ghiorso et al 1952 Nobelium E. D. Donets, V. A. Shchegolev and V. A. Ermakov 1966 Dubnium A. Ghiorso, M. Nurmia, K. Eskola, J. Harris and P. Eskola 1970 Tennessine Y. Oganessian et al 2010

Elements With Their Valence

The following table illustrates significant elements and their valence −