Showing posts with label introduction. Show all posts
Showing posts with label introduction. Show all posts
Friday, September 23, 2016
The Sun And It s Introduction Find The Best Online Information
The Sun And It s Introduction Find The Best Online Information
Sun,
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closest star to Earth. The Sun is a huge mass of hot, glowing gas. The strong gravitational pull of the Sun holds Earth and the other planets in the solar system in orbit. The Sun’s light and heat influence all of the objects in the solar system and allow life to exist on Earth.
The Sun is an average star—its size, age, and temperature fall in about the middle of the ranges of these properties for all stars. Astronomers believe that the Sun is about 4.6 billion years old and will keep shining for about another 7 billion years.
For humans, the Sun is beautiful and useful, but also powerful and dangerous. As Earth turns, the Sun rises over the eastern horizon in the morning, passes across the sky during the day, and sets in the west in the evening. This movement of the Sun across the sky marks the passage of time during the day (see Sundial). The Sun’s movement can produce spectacular sunrises and sunsets under the right atmospheric conditions. At night, reflected sunlight makes the Moon and planets bright in the night sky.
The Sun provides Earth with vast amounts of energy every day. The oceans and seas store this energy and help keep the temperature of Earth at a level that allows a wide variety of life to exist. Plants use the Sun’s energy to make food, and plants provide food for other organisms. The Sun’s energy also creates wind in Earth’s atmosphere. This wind can be harnessed and used to produce power.While it lights our day and provides energy for life, sunlight can also be harmful to people. Human skin is sensitive to ultraviolet light emitted from the Sun. Earth’s atmosphere blocks much of the harmful light, but sunlight is still strong enough to burn skin under some conditions (see Burn). Sunburn is one of the most important risk factors in the development of skin cancers, which can be fatal. Sunlight is also very harmful to human eyes. A person should never look directly at the Sun, even with sunglasses or during an eclipse. The Sun influences Earth with more than just light. Particles flowing from the Sun can disrupt Earth’s magnetic field, and these disruptions can interfere with electronic communications.
Characteristics of the Sun, The distance between the sun and the earth varies because the earth travels in an elliptical rather than circular orbit. The distance is roughly 100 times the sun’s diameter. Turbulence in the photosphere forms granules of various sizes and sunspots. Temperature is a measure of kinetic energy. The dense plasma in the center of the sun is roughly 2500 times hotter than the surface. Gases in the corona have escaped from the sun’s surface and have a very high velocity. The sun’s spectral type, G2, indicates that it is composed of hydrogen, helium, calcium,iron and other metals.
II PHYSICAL CHARACTERISTICS
The Sun is large and massive compared to the other objects in the solar system. The Sun’s radius (the distance from its center to its surface) is 695,508 km (432,169 mi), 109 times as large as Earth’s radius. If the Sun were hollow, a million Earths could fit inside it. The Sun has a mass of 1.989 × 1027 metric tons. This number is very large. Written out, it would be the digits 1989 followed by 24 zeroes. The Sun is 333,000 times as massive as Earth is. Despite its large mass, the Sun has a lower density, or mass per unit volume, than Earth. The Sun’s average density is only 1.409 g/cu cm (1.188 oz/cu in), which is a quarter of the average density of Earth.
The Sun produces an enormous amount of light. It generates 3.83 × 1026 watts of power in the form of light. In comparison, an incandescent lamp emits 60 to 100 watts of power. The temperature of the outer, visible part of the Sun is 5500°C (9900°F).
From Earth the Sun looks small, because it is far away. Its average distance from Earth is 150 million km (93 million mi). Light from the Sun takes about eight minutes to reach Earth. This light is still strong enough when it reaches Earth, however, to damage human eyes when viewed directly. The Sun is much closer to Earth than any other star is. The Sun’s nearest stellar neighbor, Proxima Centauri (part of the triple star Alpha Centauri), is 4.3 light-years from our solar system, meaning light from Proxima Centauri takes 4.3 years to reach the Sun. The Sun is so much closer to Earth than all other stars are that the intense light of the Sun keeps us from seeing any other stars during the day.
A Importance to Earth
Earth would not have any life on it without the Sun’s energy, which reaches Earth in the form of heat and light. This energy warms our days and illuminates our world. Green plants absorb sunlight and convert it to food, which these plants then use to live and grow. In this process, the plants give off the oxygen that animals breathe. Animals eat these plants for nourishment. All plant and animal life relies on the Sun’s presence
The Sun also provides—directly or indirectly—much of the energy on Earth that people use for fuel (see Solar Energy). Devices called solar cells turn sunlight into electricity. Sunlight can heat a gas or liquid, which can then be circulated through a building to heat the building. The energy stored in fossil fuels originally came from the Sun. Ancient plants used sunlight as fuel to grow. Animals consumed these plants. The plants and animals stored the energy of sunlight in the organic material that composed them. When the ancient plants and animals died and decayed, this organic material was buried and gradually turned into the petroleum, coal, and natural gas people use today. The Sun’s energy produces the winds and the movements of water that people harness to produce electricity (see Wind Energy; Water Power). The Sun heats Earth’s oceans and land, which in turn heat the air and make it circulate in the atmosphere as wind. The Sun fuels Earth’s water cycle, evaporating water from the oceans, seas, and lakes. This water returns to the ground in the form of precipitation, flowing back to the oceans through the ground and in rivers. The energy of water’s motion in rivers can be harnessed with dams.
B Role in the Solar System
The Sun’s gravitational pull holds the solar system together. The planets, asteroids, comets, and dust that make up our solar system are strongly attracted to the Sun’s huge mass. This gravitational attraction keeps these bodies in orbit around the Sun. The Sun also influences the solar system with its diffuse outer atmosphere, which expands outward in all directions. This expanding atmosphere fills the solar system with a constant flow of tiny, fast, electrically charged particles. This flow is called the solar wind. The region through which the solar wind blows is called the heliosphere. Estimates vary about the extent of the heliosphere, ranging from about 86 to about 100 times the distance between Earth and the Sun. Interstellar winds may give the heliosphere an egg shape. The solar wind spreads out as it leaves the Sun. The point at which the solar wind is so diffuse that it stops having an effect on its surroundings is called the heliopause. The heliopause marks the outer edge of the solar system. Within the heliosphere, the Sun provides most of the heat and light that are present, and the particles in the solar wind interact with the planets and satellites in the solar system. The solar wind causes auroras—displays of colored light—in the atmosphere of Earth’s polar regions. The solar wind also carries remnants of the Sun’s magnetic field, which affect the magnetic fields of the planets and larger satellites. The solar wind pushes the planets’ magnetic fields away from the Sun, turning them into elongated, windsock shapes. For more information, see the Solar Wind section of this article.
III THE SUN AS A STAR
The Sun is extremely important to Earth and to our solar system, but on the scale of the galaxy and the universe, the Sun is just an average star. It is one of hundreds of billions of stars in our galaxy, the Milky Way, which is just one of more than 100 billion galaxies in the observable universe
The Sun’s Place in the Milky Way
The Milky Way Galaxy contains about 400 billion stars. All of these stars, and the gas and dust between them, are rotating about a galactic center. Stars that are farther away from the center move at slower speeds and take longer to go around it.
The Sun is located in the outer part of the galaxy, at a distance of 2.6 × 1017 km (1.6 × 1017 mi) from the center. The Sun, which is moving around the center at a velocity of 220 km/s (140 mi/s), takes 250 million years to complete one trip around the center of the galaxy. The Sun has circled the galaxy more than 18 times during its 4.6-billion-year lifetime.
B Comparisons with Other Stars
A star is a ball of hot, glowing gas that is hot enough and dense enough to trigger nuclear reactions, which fuel the star. In comparing the mass, light production, and size of the Sun to other stars, astronomers find that the Sun is a perfectly ordinary star. It behaves exactly the way they would expect a star of its size to behave. The main difference between the Sun and other stars is that the Sun is much closer to Earth.Most stars have masses similar to that of the Sun. The majority of stars’ masses are between 0.3 to 3.0 times the mass of the Sun. Theoretical calculations indicate that in order to trigger nuclear reactions and to create its own energy—that is, to become a star—a body must have a mass greater than 7 percent of the mass of the Sun. Astronomical bodies that are less massive than this become planets or objects called brown dwarfs. The largest accurately determined stellar mass is of a star called V382 Cygni and is 27 times that of the Sun.The range of brightness among stars is much larger than the range of mass. Astronomers measure the brightness of a star by measuring its magnitude and luminosity. Magnitude allows astronomers to rank how bright, comparatively, different stars appear to humans. Because of the way our eyes detect light, a lamp ten times more luminous than a second lamp will appear less than ten times brighter to human eyes. This discrepancy affects the magnitude scale, as does the tradition of giving brighter stars lower magnitudes. The lower a star’s magnitude, the brighter it is. Stars with negative magnitudes are the brightest of all. Magnitude is given in terms of absolute and apparent values. Absolute magnitude is a measurement of how bright a star would appear if viewed from a set distance away. By convention, this distance is 10 parsecs, or 32.6 light-years. Apparent magnitude measures how bright a star appears from Earth. The Sun’s absolute magnitude is 4.8. The brightest known stars have absolute magnitudes of about -9 (lower magnitudes mean brighter stars), and the dimmest known stars have absolute magnitudes of about 20. The apparent magnitude of the Sun is -26.72. The apparent magnitude of the brightest star in Earth’s night sky, Sirius, is -1.46. The dimmest stars that can be seen from Earth with unaided eyes have apparent magnitudes of about 6.
Astronomers also measure a star’s brightness in terms of its luminosity. A star’s absolute luminosity or intrinsic brightness is the total amount of energy radiated by the star per second. Luminosity is often expressed in units of watts. The Sun’s absolute luminosity is 3.86 × 1026 watts. The absolute luminosity of stars ranges from one thousandth of the luminosity of the Sun to 10 million times that of the Sun.Another way of measuring brightness is to measure the amount of light that reaches an observer. This measurement is called apparent brightness or apparent luminosity. Apparent luminosity depends on the absolute luminosity of a star and the distance from the star to the observer. Apparent luminosity becomes smaller as distance from the star to the observer becomes larger. From Earth, the apparent luminosity of the Sun is 10 billion times greater than the apparent luminosity of the next brightest star, Sirius, because the Sun is so much closer to Earth. The radius of the Sun is about average among stars. The radii of most stars fall between 0.2 and 15 times the Sun’s radius, although some giant stars are hundreds of times larger than the Sun. Larger stars usually have larger absolute luminosities.We receive much more energy from the Sun than from other stars, because the Sun is so nearby. The Sun’s proximity also allows scientists to study its face in detail. A modest telescope can resolve solar structures that are 700 km (400 mi) across—about the distance from Boston, Massachusetts, to Washington, D.C. That level of detail is comparable to seeing the features on a coin from 1 km (0.6 mi) away. Other stars are so distant that the details on their surfaces remain unresolved with even the largest telescopes.
C Composition of the Sun
The Sun is a second-generation star, meaning that some of its material came from former stars. Some stars in our galaxy are nearly as old as the expanding universe, which scientists believe originated in the big bang explosion about 14 billion years ago (see Big Bang Theory). In contrast, the Sun is only 4.6 billion years old.The first stars were composed only of the hydrogen and helium produced in the early universe. These stars are called first-generation stars. Although hydrogen is also the main ingredient of the Sun, it contains heavier elements, such as carbon, nitrogen, and oxygen, as well. These elements formed inside first-generation stars that lived and died before the Sun was born. When these massive, short-lived stars used up their internal fuel, they exploded and ejected the heavier elements into interstellar space. The Sun formed from this material, making it a second-generation star.
D The Sun’s Remote Past and Distant Future
The Sun and planets in our solar system formed when a rotating cloud of dust and gas in space collapsed, or condensed, due to the gravitational attraction between the particles in the cloud. A nearby supernova explosion may have triggered the collapse, or a random fluctuation in the density of the cloud may have started the process. The Sun formed at the center of the spinning cloud, while the debris that condensed into planets formed a flattened disk revolving around the Sun. When the Sun reached its present size about 4.6 billion years ago, it was hot enough inside to ignite the nuclear reactions that make it glow.
The Sun cannot shine forever, because it will eventually use up its present fuel. The nuclear fusion reactions that make the Sun glow (for more information, see the section entitled The Sun’s Energy in this article) depend on the element hydrogen, but the hydrogen in the Sun’s core will eventually run out. Nuclear reactions have converted about 37 percent of the hydrogen originally in the Sun’s core into helium. Astronomers estimate that the Sun’s core will run out of hydrogen in about 7 billion years.
The Sun will grow steadily brighter as time goes on and more helium accumulates in its core. Even as the supply of hydrogen dwindles, the Sun’s core must keep producing enough pressure to keep the Sun from collapsing in on itself. The only way it can do this is to increase its temperature. The increase in temperature raises the rate at which nuclear reactions occur and makes the Sun brighter. In 3 billion years, the Sun will be hot enough to boil Earth’s oceans away. Four billion years thereafter, the Sun will have used up all its hydrogen and will balloon into a giant star that engulfs the planet Mercury. At this point in its life, the Sun will be a red giant star. The Sun will then be 2,000 times brighter than it is now, and hot enough to melt Earth’s rocks. At this time the outer solar system will get warmer and more habitable. The icy moons of the giant planets may warm enough to be covered by water instead of ice.
When the giant Sun uses up its fuel, it will no longer be able to support the weight of its inner layers, and they will begin to collapse toward the core, eventually producing a small, dense, cool star called a white dwarf. The Sun will then have about the same radius as Earth has, but it will be much denser and more massive than Earth. The Sun will become a white dwarf star about 8 billion years from now. After it becomes a white dwarf, it will cool slowly for billions of years, eventually becoming so cool that it will no longer emit light.
IV THE SUN’S ENERGY
The Sun produces an amazing amount of light and heat through nuclear reactions (Nuclear Energy). The process that produces the Sun’s energy is called nuclear fusion. In nuclear fusion, two atoms come together to produce a heavier atom. Fusion reactions release energy and tiny elementary particles.
A Scale of the Sun’s Energy
In just one second the Sun emits more energy than humans have used in the last 10,000 years. The Sun has been shining relatively steadily for 4.6 billion years. Until the early 20th century, humans did not know of any process that could explain the energy production of the Sun. Even if a fire, such as those that occur on Earth, were as large as the Sun, the fire would consume the mass of the Sun in a few thousand years.
Scientists now know that the Sun is mainly composed of hydrogen, the lightest and most abundant element in the universe. The Sun contains an enormous amount of hydrogen, however, which makes the Sun very massive. All matter inside the Sun is gravitationally attracted to all the other matter in the Sun, and this attraction tends to pull the Sun’s mass together. This inward pull creates high pressures and temperatures inside the Sun.
The center is so violent and hot that collisions between atoms break the hydrogen atoms apart into their subatomic ingredients. A hydrogen atom is made up of a nucleus that contains a positively charged proton, and a negatively charged electron that orbits the nucleus. In the Sun, collisions separate the electron from the nucleus, freeing each to move about the solar interior. The positively charged nuclei, or protons, are called ions. A gas in which particles are ionized, or have electric charges, is called plasma. Scientists often consider plasma, such as the material inside the Sun, to be a fourth state of matter—the three more familiar states of matter are gas, liquid, and solid. See also Atom.
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Tuesday, August 16, 2016
Introduction Definition And Major Branches Of Chemistry
Introduction Definition And Major Branches Of Chemistry
Chemistry,
Chemists, scientists who study chemistry, are more interested in the materials of which an object is made than in its size, shape, or motion. Chemists ask questions such as what happens when iron rusts, why iron rusts but tin does not, what happens when food is digested, why a solution of salt conducts electricity but a solution of sugar does not, and why some chemical changes proceed rapidly while others are slow. Chemists have learned to duplicate and produce large quantities of many useful substances that occur in nature, and they have created substances whose properties are unique.
Much of chemistry can be described as taking substances apart and putting the parts together again in different ways. Using this approach, the chemical industry produces materials that are vital to the industrialized world. Resources such as coal, petroleum, ores, plants, the sea, and the air yield raw materials that are turned into metal alloys; detergents and dyes; paints, plastics, and polymers; medicines and artificial implants; perfumes and flavors; fertilizers, herbicides, and insecticides. Today, more synthetic detergent is used than soap; cotton and wool have been displaced from many uses by artificial fibers; and wood, metal, and glass are often replaced by plastics.
A living organism is a complex chemical factory in which precisely regulated reactions occur between thousands of substances.
Chemistry is often called the central science, because its interests lie between those of physics (which focuses on single substances) and biology (which focuses on complicated life processes). A living organism is a complex chemical factory in which precisely regulated reactions occur between thousands of substances. Increased understanding of the chemical behavior of these substances has led to new ways to treat disease and has even made it possible to change the genetic makeup of an organism. For example, chemists have produced strains of food plants that are hardier than the parent strain.
Because the field of chemistry covers such a broad range of topics, chemists usually specialize. Thus, chemistry is divided into a number of branches, some of which are discussed at the end of this article. Nevertheless, the process of learning the properties of a substance and of taking it apart is fundamental to nearly all of chemistry.
The first step in investigating a complex material is to try to break it down into simpler substances. Sometimes this is easy. A mixture of brass and iron tacks, for instance, could be sorted with a magnet or even by hand. Getting the salt out of brine or seawater is a little harder, but the water can be evaporated, leaving the salt. Changes of this sort, which do not alter the fundamental nature of the components of the mixture but do modify their physical condition, are called physical changes. Grinding a rock, hammering a metal, or compressing a gas causes physical changes. Another example of physical change is the melting of ice, in which water changes from the solid to the liquid state.
Salt and water may not only be separated when in solution, but each may be broken down into other substances. This, however, involves a different kind of change—one that usually requires more energy than a physical change and that alters the fundamental nature of the material. This type of change is called a chemical change. By applying electrical energy, water can be broken down into two gases, hydrogen and oxygen. Hydrogen is a light gas that burns; oxygen is a gas that is necessary to sustain animal life. Salt can be broken down by melting it, then passing an electric current through it. This produces a pungent yellow-green gas called chlorine and a soft, silvery metal called sodium, which burns readily in air.
Some materials can be broken down simply by heating them. Other materials yield to attack by another substance; for example, iron oxide ore heated with coke yields metallic iron.
II ELEMENTS AND COMPOUNDS
More than 100 chemical elements—substances that cannot be decomposed or broken into more elementary substances by ordinary chemical means—are known to exist in the universe. However, several of these elements, such as the so-called transuranium elements, have not been found in nature and can only be produced artificially.
Russian chemist Dmitri Ivanovich Mendeleyev and German physicist Julius Lothar Meyer independently developed the periodic law of the chemical elements at about the same time in the late 19th century. Mendeleyev is generally credited with the findings, because he established the periodic law in 1869, and Meyer established this chemical law in 1870. Both discovered that arranging the elements in order of increasing atomic mass produced a table of chemical properties and reactivity patterns that were regularly repeated. This phenomenon—known as the periodic law—is most often represented in the periodic table of the elements (see Atom).
A Elements
Hydrogen, oxygen, chlorine, sodium, and iron are examples of elements. Elements cannot be resolved into simpler substances by ordinary heat, light, electricity, or attack by other substances. To say that elements can never be broken down would not be accurate, but breaking them down takes millions of times more energy than can be applied by ordinary means. It requires either special equipment, such as a particle accelerator, or temperatures like those in the interior of the sun. An element can therefore be defined as a substance that cannot be broken down into simpler substances by ordinary means.
Ninety elements are known to occur in nature, and 22 more have been made artificially. Out of this limited number of elements, all the millions of known substances are made.
Abbreviating the names of the elements is often convenient. For each element, a symbol has been chosen that consists of one or two letters. The symbols are derived from the names of the elements; for example, H stands for hydrogen, He for helium, C for carbon, and so on. The abbreviations are not always derived from the English names, however. The symbol Fe for iron comes from the Latin ferrum, and W for tungsten comes from the German wolfram. These symbols are internationally recognized and are used even by people whose native languages do not use the Roman alphabet, such as Russian and Japanese.
B Compounds Salt, water, iron rust, and rubber are examples of compounds. A compound is made up of elements, but it looks and behaves quite differently, as a rule, from any of its component elements. Iron rust, for example, does not look and feel like its components: oxygen gas and iron metal. Some synthetic fabrics, with fibers made from coal, air, and water, do not feel at all like any of the components that make them up. This individuality of properties, as well as other qualities, distinguishes a compound from a simple mixture of the elements it contains. Another important characteristic of a compound is that the weight of each element in the compound always has a fixed, definite ratio to the weight of the other elements in the compound. For example, water always breaks down into 2.016 parts of hydrogen by weight to 16.000 parts of oxygen by weight, which is a ratio of about 1 to 8, regardless of whether the water came from the Mississippi River or the ice of Antarctica. In other words, a compound has a definite, invariable composition, always containing the same elements in the same proportions by weight; this is the law of definite proportions.
Many elements combine in more than one ratio, giving different compounds. In addition to forming water, hydrogen and oxygen also form hydrogen peroxide. Hydrogen peroxide has 2.016 parts of hydrogen to 32 parts of oxygen; that is, 1.008 parts of hydrogen to 16 parts of oxygen. Water, as stated above, has 2.016 parts of hydrogen to 16 parts of oxygen. The figure 2.016 is twice 1.008. This example illustrates the law of multiple proportions: When two elements combine to form more than one compound, the element whose mass varies combines with a fixed mass of the second element weights in a simple whole-number ratio such as 2:1, 3:1, or 3:2.
C Atoms and Molecules
The concepts of atoms and of the groups of linked atoms called molecules are the foundation of all chemistry (see Atom). An atom is the smallest unit of an element that has the properties of the element; a molecule is the smallest unit of a compound or the form of an element in which atoms bind together that has the properties of the compound or element.
The idea of atoms is an old one. Greek philosopher Leucippus and his student Democritus appear to have originated the idea during the 4th and 5th centuries bc. According to them, matter consisted of small, indivisible particles called atoms. All atoms were made of the same basic material, but neither philosopher stated what this material was. The atomic theory was developed further by another Greek philosopher, Epicurus, who added the property of weight to the atoms and attributed a horizontal, as well as a vertical, motion to them in order to explain how atoms combine to form matter. These ideas were restated by Roman poet Lucretius in the 1st century bc.
In the 18th century ad, English schoolmaster John Dalton developed his well-known atomic theory, which explained the laws of definite and multiple proportions. Convincing proof that atoms exist, however, has only been generated since 1900. Much, but not all, of this proof came from the study of radioactivity and of energetic particles. When Lucretius watched dust particles dancing in a sunbeam and said that they were being battered by the invisible blows of restless atoms, he was basically right. True, most of the dancing was caused by air currents, yet even in still air, specks of dust or smoke are in constant motion, as are minute particles suspended in water. This constant random movement of particles is the so-called Brownian motion. Two thousand years after Lucretius, French scientist Jean-Baptiste Perrin, armed with a microscope and, more importantly, a mathematical theory, measured the random motions of suspended dye particles and calculated the number of the invisible molecules whose collisions were causing the visible dye particles to move. This way of counting molecules helped substantiate the existence of atoms and molecules.
Chemistry, Organic, branch of chemistry in which carbon compounds and their reactions are studied. A wide variety of classes of substances—such as drugs, vitamins, plastics, natural and synthetic fibers, as well as carbohydrates, proteins, and fats—consist of organic molecules. Organic chemists determine the structures of organic molecules, study their various reactions, and develop procedures for the synthesis of organic compounds. Organic chemistry has had a profound effect on modern life: It has improved natural materials and it has synthesized natural and artificial materials that have, in turn, improved health, increased comfort, and added to the convenience of nearly every product manufactured today.
The advent of organic chemistry is often associated with the discovery in 1828 by the German chemist Friedrich Wöhler that the inorganic, or mineral, substance called ammonium cyanate could be converted in the laboratory to urea, an organic substance found in the urine of many animals. Before this discovery, chemists thought that intervention by a so-called life force was necessary for the synthesis of organic substances. Wöhlers experiment broke down the barrier between inorganic and organic substances. Modern chemists consider organic compounds to be those containing carbon and one or more other elements, most often hydrogen, oxygen, nitrogen, sulfur, or the halogens, but sometimes others as well.
Chemistry, Physical, field of science that applies the laws of physics to elucidate the properties of chemical substances and clarify the characteristics of chemical phenomena. The term physical chemistry is usually applied to the study of the physical properties of substances, such as vapor pressure, surface tension, viscosity, refractive index, density, and crystallography, as well as to the study of the so-called classical aspects of the behavior of chemical systems, such as thermal properties, equilibria, rates of reactions, mechanisms of reactions, and ionization phenomena (see Chemical Reaction; Heat; Heat Transfer; Ionization). In its more theoretical aspects, physical chemistry attempts to explain spectral properties of substances in terms of fundamental quantum theory; the interaction of energy with matter; the nature of chemical bonding; the relationships correlating the number and energy states of electrons in atoms and molecules with the observable properties shown by these systems; and the electrical, thermal, and mechanical effects of individual electrons and protons on solids and liquids.
Chemistry, Inorganic, study of the structure, properties, and reactions of the chemical elements and their compounds. Inorganic chemistry does not include the investigation of hydrocarbons—compounds composed of carbon and hydrogen that are the parent material of all other organic compounds. The study of organic compounds is called organic chemistry.
Inorganic chemists have made significant advances in understanding the minute particles that compose our world. These particles, called atoms, make up the elements, which are the building blocks of all the compounds and substances in the world around us. Just as the entire English language is constructed from combinations of the 26 letters in the alphabet, all chemical substances are made from combinations of the 112 chemical elements found on the periodic table (see Periodic Law).
Ninety elements are known to occur in nature, and 22 more have been made artificially. Elements—which include substances such as oxygen, nitrogen, and sulfur—cannot be broken into more elementary substances by ordinary chemical means. The elements are arranged in the periodic table in rows from the lightest element (hydrogen) to the heaviest (ununbium). These rows are split so that elements with similar chemical properties fall in the same columns (for more information, see the Periodic Law section of this article).
The smallest representative unit of an element is an atom (see Atom). (For example, the smallest representative of the element helium (He) is a helium atom.) When atoms that come in close contact have a sufficiently large attractive force, a chemical bond, or binding link, forms between them. The combination of two or more atoms bonded together is called a molecule. A molecule is the smallest particle of a substance possessing the specific chemical properties of that substance. For example, an atom of oxygen (O) combines with two atoms of hydrogen (H) to form a water molecule (H2O). While molecules of H2O possess the properties of water, individual oxygen and hydrogen atoms do not.
Much of chemistry can be described as breaking substances apart and putting chemical components together to form new substances. This process is accomplished by breaking chemical bonds between atoms and creating new bonds, a process known as a chemical reaction.
Analytical Chemistry, one of the major branches of modern chemistry. It is subdivided into two main areas, qualitative and quantitative analysis. The former involves the determination of unknown constituents of a substance, and the latter concerns the determination of the relative amounts of such constituents. See Chemical Analysis.
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