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General Science - Chemistry (Elements):

Written By STPORTAL on Sunday, March 18, 2012 | 2:47 PM

General Science - Chemistry (Elements):

Elements are substances that cannot be decomposed or broken into more elementary substances by ordinary chemical means. Hydrogen, oxygen, chlorine, sodium, and iron are examples of elements. Ninety two elements are known to occur in nature, and 22 more have been made artificially. Elements having atomic number greater than 92 are Transuranium elements.

Some Common Elements and their applications
Air is a mixture of gases ; these gases consist primarily of the elements nitrogen, oxygen, argon, and smaller amounts of hydrogen, carbon dioxide, water vapor, helium, neon, krypton, xenon, and others.

Nitrogen is the most abundant constituent in the atmosphere composes about four-fifths(78.03) percent by volume of the atmosphere. It is inert and serves as a moderate supporter of combustion. Nitrogen fixation is a process by which certain bacteria in the soil convert atmospheric nitrogen as nitrate that can be absorbed by plants . Nitrous oxide is known as laughing gas. Mixed with oxygen, nitrous oxide is used as an anesthetic for some types of surgery. Liquid nitrogen is used as coolant in cryogenics. The element occurs in the combined state in minerals, of which saltpetre (KNO3) and chile saltpetre ( NaNO3) are commercially important products.

Oxygen is the most abundant element in the earth. It was discovered by Joseph priestly. Oxygen composes 21 percent by volume. It is used in high-temperature welding torches, administered to patients whose breathing is impaired and oxygen-enriched air is used in open-hearth furnaces for steel manufacture.

Most of the oxygen produced is used to make a mixture of carbon monoxide and hydrogen called synthesis gas, used for the synthesis of methanol and ammonia. High-purity oxygen is used also in the metal-fabrication industries; in liquid form it is of great importance as a propellant for guided missiles and rockets.

Argon is the third most prevalent gas in the earth̢۪s atmosphere. Argon is also used in one type of neon lamp giving blue light whereas pure neon gives a red light. It is preferred because it requires a lower voltage than neon.

Hydrogen exits as a gas at room temperature and is highly flammable. When hydrogen gas burns in air it forms water. In stars, hydrogen nuclei combine with each other in nuclear reactions to form helium atoms. The isotopes of Hydrogen are Deuterium and tritium. Researches have been conducting to use hydrogen as fuel for automobiles, refrigerators and airplanes. Spacecrafts use hydrogen as fuel that reacts with fluorine or oxygen. Nuclear plants use D2O as a moderator.

Carbon dioxide
Carbon dioxide does not burn and support ordinary combustion; it is used in fire extinguishers. Solid carbon dioxide is known as Dry ice widely used as refrigerant. The presence of carbon dioxide in the blood stimulates breathing. For this reason, CO2 is added to the oxygen or ordinary air in artificial respiration and to the gases used in anaesthesia.

Inert gas
An Inert gas is a non-reactive gas . In order of increasing atomic weight are helium, neon, argon, krypton, xenon and radon. Liquefied noble gases, particularly xenon, are employed as solvents in infrared spectroscopy because they are transparent to infrared radiation and therefore do not obscure the spectra of the dissolved substances.

Methane also know as marsh gas, gas composed of carbon and hydrogen with formula CH4, the first member of the paraffin or alkane series of hydrocarbons. It is lighter than air, colorless, odorless, and flammable. It occurs in natural gas, as firedamp in coal mines, as a by-product of petroleum refining, and as a product of decomposition of matter in swamps. It is a major component in the atmosphere of the outer planets, Jupiter, Saturn, Uranus, and Neptune.

Iron is a metal extracted from iron ore, and is hardly ever found in the free (elemental) state. In order to obtain elemental iron, the impurities must be removed by chemical reduction in blast furnace. Depending upon the carbon content Iron can be classified into
·         Pig Iron (4%-5%)
·         Cast iron(2-3.5%)
·         carbon steel(0.5-1.5%)
·         Wrought Iron( < 0.5%).

Sodium is a constituent of many household products, including table salt and baking soda. In its pure form, however, it reacts explosively with water and oxidizes immediately upon exposure to the atmosphere. Reactions that produce useful chemicals can also cause environmental problems. Sulfur dioxide (SO2), for instance, produced by burning sulfur in air is the precursor of sulfuric acid (H2SO4), which in turn is used to produce fertilizer. Sulfur, however, is a common impurity in fossil fuels used for home heating and the production of electricity. Large amounts of SO2 are thus produced under uncontrolled conditions, causing both local air pollution as well as the larger problems of acid rain.

The halogens
The halogens are a chemical series. They are the elements in Group 17 (old-style: VII or VIIA) of the periodic table: fluorine, chlorine, bromine, iodine, and astatine.

·         Chlorine gas is greenish yellow, is two and one half times as heavy as air, has an intensely disagreeable suffocating odor, and is exceedingly poisonous. It is a powerful oxidizing, bleaching, and disinfecting agent. Chlorine is an important chemical in water purification, in disinfectants in bleach and in mustard gas.
·         Bromine is a red volatile liquid at room temperature which has a reactivity between chlorine and iodine.
·         Astatine is radioactive and heaviest of Halogens.
·         Iodine is a bluish-black, lustrous solid and least reactive halogen. The deficiency of Iodine causes Goitre. Potassium Iodide is used in Photography. Iodine 131 is used as a tracer in medicine.

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