Atomic theory

In chemistry and physics, atomic theory is a scientific theory of the nature of matter, which states that matter is composed of discrete units called atoms. It began as a philosophical concept in ancient Greece and entered the scientific mainstream in the early 19th century when discoveries in the field of chemistry showed that matter did indeed behave as if it were made up of atoms; the word atom comes from the Ancient Greek adjective atomos, meaning "indivisible". 19th century chemists began using the term in connection with the growing number of irreducible chemical elements. Around the turn of the 20th century, through various experiments with electromagnetism and radioactivity, physicists discovered that the so-called "uncuttable atom" was a conglomerate of various subatomic particles which can exist separately from each other. In fact, in certain extreme environments, such as neutron stars, extreme temperature and pressure prevents atoms from existing at all. Since atoms were found to be divisible, physicists invented the term "elementary particles" to describe the "uncuttable", though not indestructible, parts of an atom.

The field of science which studies subatomic particles is particle physics, it is in this field that physicists hope to discover the true fundamental nature of matter. The idea that matter is made up of discrete units is a old idea, appearing in many ancient cultures such as Greece and India; the word "atom", meaning "uncuttable", was coined by the Pre-Socratic Greek philosophers Leucippus and his pupil Democritus. Democritus taught that atoms were infinite in number and eternal, that the qualities of an object result from the kind of atoms that compose it. Democritus's atomism was refined and elaborated by the Greek philosopher Epicurus, by the Roman Epicurean poet Lucretius. During the Early Middle Ages, atomism was forgotten in western Europe. During the 12th century, atomism became known again in western Europe through references to it in the newly-rediscovered writings of Aristotle. In the 14th century, the rediscovery of major works describing atomist teachings, including Lucretius's De rerum natura and Diogenes Laërtius's Lives and Opinions of Eminent Philosophers, led to increased scholarly attention on the subject.

Nonetheless, because atomism was associated with the philosophy of Epicureanism, which contradicted orthodox Christian teachings, belief in atoms was not considered acceptable by most European philosophers. The French Catholic priest Pierre Gassendi revived Epicurean atomism with modifications, arguing that atoms were created by God and, though numerous, are not infinite. Gassendi's modified theory of atoms was popularized in France by the physician François Bernier and in England by the natural philosopher Walter Charleton; the chemist Robert Boyle and the physicist Isaac Newton both defended atomism and, by the end of the 17th century, it had become accepted by portions of the scientific community. Near the end of the 18th century, two laws about chemical reactions emerged without referring to the notion of an atomic theory; the first was the law of conservation of mass associated with the work of Antoine Lavoisier, which states that the total mass in a chemical reaction remains constant.

The second was the law of definite proportions. First established by the French chemist Joseph Louis Proust in 1799, this law states that if a compound is broken down into its constituent chemical elements the masses of the constituents will always have the same proportions by weight, regardless of the quantity or source of the original substance. John Dalton studied and expanded upon this previous work and defended a new idea known as the law of multiple proportions: if the same two elements can be combined to form a number of different compounds the ratios of the masses of the two elements in their various compounds will be represented by small whole numbers; this is a common pattern in chemical reactions, observed by Dalton and other chemists at the time. Dalton himself discovered that oxygen will combine with a certain amount of nitrous gas to form nitric acid, or twice that amount to form nitrous acid — a ratio of 1:2. Joseph Proust discovered that 100 parts of iron will combine with either 42 parts of oxygen.

Dalton found that an atomic theory of matter could elegantly explain this pattern, as well as Proust's law of definite proportions. In the case of Proust's tin oxides, one tin atom will combine with either one or two oxygen atoms to form either the first or the second oxide of tin. Dalton believed atomic theory could explain why water absorbed different gases in different proportions - for example, he found that water absorbed carbon dioxide far better than it absorbed nitrogen. Dalton hypothesized this was due to the differences in mass and complexity of the gases' respective particles. Indeed, carbon dioxide molecules are larger than nitrogen molecules. Dalton proposed that each chemical element is composed of atoms of a single, unique type, though they cannot be altered or destroyed by chemical means, they can combine to form more complex structures; this marked the first scientific theory of the atom, since Dalton reached his conclusions by experimentation and examination of the results in an empirical fashion.

In 1803 Dalton orally presented his first list of relative atomic weights for a number of substances. This paper w

1990–91 Crystal Palace F.C. season

During the 1990–91 English football season, Crystal Palace F. C. competed in the Football League First Division. In their second consecutive season in the First Division, Crystal Palace finished an astonishing third, their highest league placing, due to Liverpool's ban from European competition being lifted, Palace did not qualify for the UEFA Cup. Palace won their first cup during the season, albeit the less significant Full Members' Cup. In the League Cup, Palace broke their record for a cup victory with an 8–0 over Southend United, in the second round first leg, with strikers Mark Bright and Ian Wright both scoring hat-tricks; the two claimed the match ball. At the end of the season, captain Geoff Thomas was named the Supporters' Player of the Year. Thomas was rewarded for his good form with a call-up to the England squad for a European Championship qualifying game against Turkey in May. Bukta remained Palace's kit manufacturers, introduced a new home kit for the season. English airline Fly Virgin remained.

Pld = Matches. Results summary Results by round Crystal Palace's score comes first Note: Flags indicate national team as defined under FIFA eligibility rules. Players may hold more than one non-FIFA nationality. Note: Flags indicate national team as defined under FIFA eligibility rules. Players may hold more than one non-FIFA nationality. Transfers in: £2,321,000 Transfers out: £850,000 Total spending: £1,471,000

Tholymis tillarga

Tholymis tillarga, the coral-tailed cloudwing, is a species of dragonfly in the family Libellulidae. It is found from tropical West Africa to Asia and the Pacific Islands. Common names include old world twister, evening skimmer, crepuscular darter, foggy-winged twister and twister, it is a medium sized dragonfly with yellowish red thorax and coral red abdomen. Its wings are transparent. Female lacks the cloudy-white patch in the hind-wings, it is a migrant with a permanent presence in humid parts of the tropics. It breeds in standing water-bodies, they are active at dawn, as well as during cloudy days. List of odonates of Sri Lanka List of odonates of India List of odonata of Kerala List of Odonata species of Australia Data related to Tholymis tillarga at Wikispecies Media related to Tholymis tillarga at Wikimedia Commons