قواعد مربوط به جمع بستن اسم ها در انگلیسی 1- بیشتر اسمهای انگلیسی را می توان با اضافه کردن s با آخر آنها به جمع تبدیل کرد. door doors book books pen Pens cat cats 2- اسمهای مختوم به s – sh – ch –x – z – ss را بوسیله es به جمع تبدیل می کنیم. box boxes church churches bus buses glass glasses 3- اسمهای مختوم به y در صورتیکه حرف مافبل y یک حرف بی صدا باشد هنگام جمع بستن y حذف و مابقی کلمه ies می گیرد. lady ladies army armies ولی چنانچه حرف ماقبل y یکی از حروف صدادار باشد، کلمه هنگام جمع بستن فقط s می گیرد. boy boys valley valleys 4- کلماتی که به حرف f یا fe ختم می شوند در هنگام جمع بستن f یا fe به ves تبدیل می شوند. leaf leaves wife wives knife knives thief thieves یادآوری: roof و proof و برخی از کلمات دیگر از این قاعده مستثنا هستند و فقط s می گیرند. 5- برخی از کلمات مفرد را بوسیله تغییر حروف صدادار آنها به جمع تبدیل می کنیم. man men tooth teeth foot feet woman women 6- برخی از کلمات مفرد را با اضافه کردن حروفی غیر از s یا es به آخرشان به جمع تبدیل می کنیم. child children criterion criteria 7- مفرد بعضی از کلمات همانند جمع آن هاست. sheep sheep fish fish
کلمات پرسشی به دو دسته تقسیم می شوند :
الف) کلمات پرسشی دسته ی اول :
بعد از کلمات پرسشی دسته ی اول همواره جمله به شکل سوالی بکار می رود.
انواع کلمه (PARTS OF SPEECH)
در دستور زبان انگلیسی هشت نوع کلمه وجود دارد:
1- اسم (Noun). مثال: Ali - book - lion - umbrella
2- صفت (Adjective) مثال: large – good – hot - beautiful
3- ضمیر (Pronoun) مثال: him – them – We - They
4- فعل (Verb) مثال: go – come – read - watch
5- قید (Adverb) مثال: well – slowly – badly - rapidly
To realize The value of a sister Ask someone Who doesn't have one.
ارزش يک خواهر را، از کسي بپرس که آن را ندارد.
To realize The value of ten years: Ask a newly Divorced couple.
ارزش ده سال را، از زوج هائي بپرس که تازه از هم جدا شده اند.
To realize The value of four years: Ask a graduate.
ارزش چهار سال را، از يک فارغ التحصيل دانشگاه بپرس.
To realize The value of one year: Ask a student who Has failed a final exam.
ارزش يک سال را، از دانش آموزي بپرس که در امتحان نهائي مردود شده است.
To realize The value of one month: Ask a mother who has given birth to a premature baby.
ارزش يک ماه را، از مادري بپرس که کودک نارس به دنيا آورده است.
To realize The value of one week: Ask an editor of a weekly newspaper.
ارزش يک هفته را، از ويراستار يک مجله هفتگي بپرس.
To realize The value of one hour: Ask the lovers who are waiting to meet.
ارزش يک ساعت را، از عاشقی که منتظر ملاقات است بپرس.
To realize The value of one-second: Ask a person who has survived an accident.
ارزش يک ثانيه را، از کسي بپرس که از حادثه اي جان سالم به در برده است.
To realize The value of one millisecond: Ask the person who has won a silver medal in the Olympics.
ارزش يک ميلي ثانيه را، از کسي بپرس که در مسابقات المپيک، مدال نقره برده است.
Time waits for no one. Treasure every moment you have. You will treasure it even more when you can share it with someone special.
زمان براي هيچکس صبر نمي کند. قدر هر لحظه خود را بدانيد. قدر آن را بيشتر خواهيد دانست، اگر بتوانيد آن را با ديگران نيز تقسيم کنيد.
To realize the value of a friend: Lose one.
براي پي بردن به ارزش يک دوست، آن را از دست بده.
Forward this letter to friends, to whom you wish good luck. Peace, love and prosperity to all .
اين نوشته را به دوستان خود يا هر کسي که برايش آرزوي خوشبختي داريد، ارسال کنيد. صلح، عشق و کاميابي ارزاني همگان باد.
Discovery of Bromine
Bromine compounds have been used since ancient times.
In the first century AD Pliny describes one of the world’s first chemical industries: dye factories making Tyrian purple. Tyrian purple (or royal purple) is an ancient purple dye obtained from a marine mollusk. A major component of the dye is the compound 6,6′-dibromoindigo.
Three people are significant in the story of the element bromine’s discovery.
First there’s German chemist Justus von Liebig, one of most famous chemists of his time. Liebig could have been credited with the independent discovery of bromine, but he squandered the opportunity.
In 1825 a salt maker sent Liebig a sample of salt spring waters from the German town of Bad Kreuznach, asking for an analysis.
The sample had a relatively high amount of bromine in it, which Liebig isolated. Without considering the substance too seriously, he concluded it was a compound of iodine and chlorine.
Only when bromine’s existence had been announced did an anguished Liebig return to the red-brown liquid to study it closely.
He then placed the bottle in his ‘mistakes cupboard’ to remind himself that preconceived ideas ruined his chance of discovering something new and to try not to make the same mistake again.
The next name in the story of bromine is Carl Lðwig (Loewig), who discovered bromine in 1825, while still a chemistry student at Heidelberg University, Germany.
Lðwig’s home town was Bad Kreuznach, where Liebig’s sample had come from. Lðwig had taken water from a salt spring in Bad Kreuznach and added chlorine to the liquid. He shook the solution with ether and found a red-brown substance dissolved in the ether. Lðwig evaporated the ether to leave a red-brown liquid: bromine.
His professor at Heidelberg asked Lðwig to prepare more of this substance for testing. By the time Lðwig had done this it was 1826 and a final name – Antoine Balard – had taken over the story of bromine’s discovery.
In 1824 Antoine Balard, aged 21, was studying the plant life in a salt marsh in Montpellier, France. He became interested in salt deposits he saw and began investigating them.
He took brine (sea water in which salts have been concentrated by evaporation of water) and crystallized salt from it. He took the remaining liquid and saturated it with chlorine.
He then distilled the solution to leave a dark red liquid.
Alert to the possibility that he had found something very interesting, Balard gave the French Academy of Science a sealed envelope containing his initial results in 1824.
He finally published his results in 1826, providing evidence that the substance he had discovered was a new ‘simple body’ – i.e. an element, not a compound.
As first to publish, he became bromine’s discoverer. Ironically, like Liebig, his first idea was that the substance was a compound of chlorine and iodine.
The French Academy named the new element after the Greek bromos for ‘stench’ because bromine, quite simply, stinks.
Geber, Jabir ibn Hayyan, born in Persia (Iran) in the 6th Century A.D. Geber systemized and brought experimental methods to alchemy. He believed all metals were based on mercury mixed in different proportions and different purities with sulfur. If the mercury and sulfur were perfectly pure and mixed in perfect proportions, they would form gold.
The periodic table we use today is based on the one devised and published by Dmitri Mendeleev in 1869.
Mendeleev found he could arrange the 65 elements then known in a grid or table so that each element had:
1. A higher atomic weight than the one on its left. For example, magnesium (atomic weight 24.3) is placed to the right of sodium (atomic weight 23.0):
"If all the elements are arranged in the order of their atomic weights, a periodic repetition of properties is obtained. This is expressed by the law of periodicity."
Dmitri Mendeleev, Principles of Chemistry, Vol. 2, 1902, P. F. Collier, p17.
"We have here a proof that there is in the atom a fundamental quantity, which increases by regular steps as one passes from one element to the next. This quantity can only be the charge on the central positive nucleus, of the existence of which we already have definite proof."
Henry Moseley, Philosophical Magazine, Vol. 26, 1913, p1030.
"The chemistry of an atom depends only on the number of electrons, which equals the number of protons and is called the atomic number. Chemistry is simply numbers, an idea Pythagoras would have liked. If you are an atom with one proton, you are hydrogen; two, helium;....."
Carl Sagan, Cosmos, 1980, Random House, p223. Photo: NASA.
Discovery of Mercury
Mercury or quicksilver has been known since ancient times. We do not know who discovered it.
Mercury was known to the ancient Chinese, Egyptians and Hindus and has been found in Egyptian tombs dating back to about 1500 B.C.
In the fourth century B.C. we find Aristotle refers to mercury in writing as ‘hydro-argyros’ – which translates as liquid-silver or water-silver.
The Romans modified the Greek name slightly, referring to mercury as Hydragyrum, from which we get mercury’s modern chemical symbol Hg.
Our modern name for the element was provided by alchemists. Alchemists observed the element’s rapid, liquid flow, and likened it to the fastest moving planet, Mercury. (The planet had been named after the fast moving Roman messenger of the gods, Mercury.)
Alchemists believed mercury was the most important of all substances because it encompassed solid and liquid, earth and heaven, and life and death. They also believed it offered the path by which base metals could become gold and represented the quintessential property of fluidity. They were wrong, of course!
Chinese emperors used mercury to prolong their lives – although in all probability it had the opposite effect. (Despite the fact that mercury is now known to be highly toxic, some traditional Chinese medicines still appear to contain high levels of mercury.)
In 1759 Adam Braun and Mikhail Lomonosov working in St. Petersburg, Russia obtained solid mercury by freezing a mercury thermometer in a mixture of snow and concentrated nitric acid. This provided strong evidence that mercury had properties similar to other metals.
In 1772 and 1774, Swedish scientist Carl W. Scheele and English chemist Joseph Priestley heated mercury oxide and found it yielded a gas that made a candle burn five times faster than normal – they had discovered oxygen.
Priestley discovered several gases, such as nitrous oxide (laughing gas) because he collected them over a bath of mercury instead of the more usual water. Unlike water, the mercury did not dissolve the gases, leaving them available for discovery.
English chemist Humphry Davy used mercury in other discovery work. For example, Davy isolated calcium for the first time, using a mercury electrode to form an amalgam with the calcium
Discovery of Tungsten
In 1779 Irish chemist Peter Woulfe deduced the existence of a new element – tungsten – from his analysis of the mineral wolframite (an iron manganese tungstate mineral).
Tungsten was isolated as tungstic oxide (WO3) in 1781, in Sweden, by Carl W. Scheele from the mineral scheelite (calcium tungstate). However he did not have a suitable furnace to reduce the oxide to the metal.
Tungsten was finally isolated by brothers Fausto and Juan Jose de Elhuyar in 1783, in Spain, by reduction of acidified wolframite with charcoal.
The element name comes from the Swedish words ‘tung sten’ meaning heavy stone.
The chemical symbol, W, comes from the original name of the element, Wolfram.
Discovery of Uranium
In ancient times uranium oxide was used to produce yellow colored ceramic glazes.
Uranium was formally discovered in 1789, in Berlin, Germany by Martin Heinrich Klaproth.
Klaproth was studying the mineral pitchblende, which was then believed to be a zinc/iron ore.
Klaproth dissolved pitchblende in nitric acid, then added potash to obtain a yellow precipitate. Adding excess potash dissolved the yellow precipitate. Such reactions were not characteristic of any known element and Klaproth concluded he had discovered a new element.
He named it after the recently discovered planet Uranus.
In 1841, French chemist Eugene-Melchior Peligot isolated uranium metal by heating uranium tetrachloride with potassium.
Discovery of Argon
Argon was the first noble gas to be discovered.
The first hint of its existence came from English scientist Sir Henry Cavendish as far back as 1785. Cavendish was unhappy that so little was known about air. He was particularly unhappy about the lack of information about the fraction of air (the majority) which was not oxygen.
He knew the nitrogen in air could be reacted with oxygen to form, ultimately, nitrous acid. He aimed to find out if ALL of the air that was not oxygen or carbon dioxide could be converted to nitrous acid. If it could, he would know that air was entirely oxygen, carbon dioxide and nitrogen.
Cavendish used an electric spark in air to react the oxygen and nitrogen to form nitrogen oxides. He then added additional oxygen until all the nitrogen had reacted.
Nitrogen oxides are acidic. Cavendish used aqueous sodium hydroxide to remove them from the apparatus. [This would also, of course, have removed any carbon dioxide that was present.] He removed the remaining oxygen using potassium polysulfides.
A small bubble of gas remained [mostly argon]. Cavendish wrote that this bubble “was not more than one hundred and twentieth of the bulk of the phlostigated air [nitrogen].” So, Cavendish is saying that air is at least 99.3 percent nitrogen/oxygen/carbon dioxide with a maximum 0.7 percent of something else. We now know that the ‘something else’, argon, is very unreactive; this enabled Cavendish to find it, but it also prevented him finding out more about it. (The giant advances in spectroscopy made by Gustav Kirchhoff and Robert Bunsen lay 85 years in the future.)
In hindsight, we can say Cavendish slightly underestimated the part of air that isn’t oxygen, nitrogen, or carbon dioxide. Despite this, he was ahead of his time. After his experiment, more than 100 years passed until scientists again began to think that something about air didn’t quite add up.
In 1892 English physicist John William Strutt (better known as Lord Rayleigh) announced that no matter how it was prepared, oxygen was always 15.882 times denser than hydrogen. This very precise work had taken ten years to complete.
Continuing to work with great attention to detail, he found that the ‘nitrogen’ in air was always denser by about 0.5 percent than nitrogen sourced from nitrogen compounds. How could this be explained? In 1893 he wrote to Nature, announcing the problem to the world. Any scientist who responded to that challenge actually had the chance of discovering a new element. None did!
In April 1894 Rayleigh wrote an academic paper about the nitrogen problem. Funnily enough, Rayleigh viewed pure nitrogen, containing no argon, as ‘abnormally light nitrogen.’ He stored it for eight months and retested it to see whether its density would increase.
Rayleigh’s paper awakened the serious interest of Scottish chemist William Ramsay, who had already been aware of the problem.
Rayleigh and Ramsay carried out further experiments, keeping in touch with one another about their progress.
In August 1894 Ramsay took air and removed its components – oxygen, carbon dioxide and nitrogen. He removed the nitrogen by reacting it with magnesium. After removing all the known gases from air, he found gas remaining that occupied one-eightieth of the original volume. Its spectrum matched no known gas.
Rayleigh and Ramsay wrote a joint paper in 1895 notifying the world of their discovery. The new gas wouldn’t react with anything, so they named it argon, from the Greek ‘argos’, meaning inactive or lazy.
In his Nobel Prize winning address, Rayleigh said: “Argon must not be deemed rare. A large hall may easily contain a greater weight of it than a man can carry.”William Ramsay discovered or codiscovered most of the other noble gases: helium, neon, krypton and xenon.
He was responsible for adding an entire new group to the periodic table. Radon was the only noble gas he didn’t discover.
Discovery of Neon
Neon was discovered in 1898 by William Ramsay and Morris Travers at University College London.
This was not the first time Ramsay had discovered a new element.
In 1894, he and Lord Rayleigh had discovered argon. Then, in 1895, Ramsay obtained the world’s first sample of helium. (Cleve and Langlet independently also obtained helium.)
Ramsay and Travers were aware an element must sit between helium and argon in the periodic table. But how could they find it?
Having found helium in a radioactive mineral, Ramsay thought it was possible he could find the new element in another such mineral. He and Travers spent some time working with a number of minerals, trying unsuccessfully to drive out some of the as yet undiscovered gas.
Aware of the history of chemistry, Ramsay knew that sometimes one new element can hide another. For example, Berzelius discovered cerium in the mineral that came to be known as cerite. Some years later Mosander, one of Berzelius’s former students, who had continued to study cerite, discovered the new element lanthanum. Lanthanum had been present in the cerite all along, but Berzelius had not found it. Ramsay wondered about the possibility of finding small amounts of the elusive new element hiding in one of his earlier discoveries, argon.
Ramsay and Travers froze a sample of argon using liquid air. They then slowly evaporated the argon under reduced pressure and collected the first gas that came off.
To obtain the gas’s spectrum, Travers applied a high voltage to the gas in a vacuum tube and we may reasonably guess that his mouth fell open at what he saw.
He later commented, “the blaze of crimson light from the tube told its own story and was a sight to dwell upon and never forget… For the moment the actual spectrum of the gas did not matter in the least, for nothing in the world gave a glow such as we had seen.”
This was the first time anyone had seen the glow of a neon light. Ramsay named the newly discovered element ‘neon’ which is Greek for ‘new.’
Discovery of Sulfur
Sulfur has been known since ancient times. In the Bible it is called brimstone. It can be found in its elemental state around volcano vents.
The name may have been derived from the Arabic ‘sufra’ meaning yellow, or the Sanskrit ‘shulbari’ meaning enemy (ari) of copper (shulba).
The Sanskrit possibility is appealing, because it carries a message about people’s knowledge of chemistry from long ago: sulfur actually does react easily with many metals, including copper. (Sanskrit is one of the oldest Indo-European languages – over 3000 years old. Despite this, it is the human language most compatible with artificial intelligence. )
When sulfur burns it produces sulfur dioxide, a poisonous gas. At one time this gas was used in New York to fumigate buildings harboring infectious diseases.
The use of burning sulfur for fumigation began several thousand years ago. In Homer’s ‘The Odyssey’ which is about 2800 years old, Odysseus says, “Bring sulfur, old nurse, that cleanses all pollution, and bring me fire, that I may purify the house with sulfur…”)
In the year 808 a Chinese text provides us with possibly the first recipe for gunpowder, containing saltpeter, sulfur and carbon.
Sulfur is also believed to have been a component of ‘Greek Fire,’ a weapon similar to a flamethrower used by the Byzantine Empire.
Sulfur became a recognized chemical element in 1789, when Antoine Lavoisier included it in his famous list of the elements.
In 1823, German chemist Eilhard Mitscherlich discovered sulfur’s allotropy: he showed that the crystal shapes of sulfur obtained from cooling molten sulfur were different from those obtained when the element crystallized from a solution.
The sulfur obtained from molten sulfur is called monoclinic sulfur, while sulfur obtained from crystallizing a solution is called rhombic sulfur. Both forms consist of S8 rings. The difference between the forms is the way the rings are arranged within a crystal.
At this time the concept of allotropy – different structural forms of the same element – had not become a formal part of chemistry. It was not until 1841 that Berzelius introduced the term to explain sulfur’s monoclinic and rhombic forms.
By the 1800s sulfur, in the form of sulfuric acid, had become the best way to judge a country’s wealth. Countries had even gone to war over sulfur.
Here’s what the great German chemist Justus Liebig had to say about it in about 1843:
“It is no exaggeration to say, we may fairly judge the commercial prosperity of a country from the amount of sulfuric acid it consumes.
(Sulfur’s price affects the price of…) bleached and printed cotton stuffs, soap, glass, etc, and remembering that Great Britain supplies America, Spain, Portugal, and the East, with these, exchanging them for raw cotton, silk, wine, raisins, indigo, etc, we can understand why the English Government should have resolved to resort to war with Naples (in 1839) in order to abolish the sulfur monopoly, which the latter power attempted recently to establish.”
Discovery of Fluorine
In 1530, German mineralogist Georgius Agricola described the use of the mineral fluorspar in metal refining. Fluorspar (which we now know is mainly calcium fluoride) was very useful because it combined with the unwanted parts of metal ores, allowing the pure metal to flow and be collected.
The element fluorine had not yet been discovered and the ‘fluor’ in fluorspar came from the Latin word ‘fluere,’ meaning ‘to flow,’ because this is what it allowed metals to do. The element name fluorine ultimately came from the ‘fluor’ in fluorspar.
Several chemists carried out experiments on fluorspar in the early 1800s including Gay Lussac, Louis Jacques Thenard, Humphry Davy, Carl Wilhelm Scheele and Joseph Priestley.
Often they produced what they called fluoric acid – now named hydrofluoric acid – a highly reactive and potentially deadly acid. Even small splashes of this acid on skin can be fatal.Several early attempts to isolate fluorine led to blindings and fatalities. English chemist Humphrey Davy wrote: “[fluoric acid] is a very active substance, and must be examined with great caution.
In 1809, French scientist Andre-Marie Ampere proposed that fluoric acid was a compound of hydrogen with a new element. He exchanged letters with Humphry Davy, and in 1813 Davy announced the discovery of the new element fluorine, giving it the name suggested to him by Ampere.
Davy wrote: “… it appears reasonable to conclude that there exists in the fluoric compounds a peculiar substance, possessed of strong attractions for metallic bodies and hydrogen… it may be denominated fluorine, a name suggested to me by M. Ampere.”
Fluorine was finally isolated in 1886, by French chemist Henri Moissan – whose own work was interrupted four times by serious poisoning caused by the element he was pursuing.
Moissan isolated fluorine by electrolysis of dry potassium hydrogen fluoride and anhydrous hydrofluoric acid.
To limit corrosion he carried out his work in a platinum container and cooled the electrolytic solution in it to -23oF (-31 oC.) The stoppers were made out of fluorite (a more modern name for our old friend fluorspar, which we began this section with). Fluorine was produced at the positive electrode.
Henri Moissan received the 1906 Nobel Prize in Chemistry for his achievement.
Discovery of Phosphorus
Hennig Brand discovered phosphorus in 1669, in Hamburg, Germany, preparing it from urine. (Urine naturally contains considerable quantities of dissolved phosphates.)
Brand called the substance he had discovered ‘cold fire’ because it was luminous, glowing in the dark.
Brand was an alchemist and, like other alchemists, he was secretive about his methods.
He did not reveal his method publicly, choosing instead to sell it to Johann Daniel Kraft and Kunckel von Lowenstern.For further payment he also revealed his secret to Gottfried Wilhelm Leibniz, better known for discovering calculus independently of Isaac Newton.
Leibniz, also thinking as an alchemist, mistakenly believed Brand might be able to discover the philosophers’ stone by producing a large quantity of phosphorus.
Brand’s method is believed to have consisted of evaporating urine to leave a black residue that was then left for a few months. The residue was then heated with sand, driving off a variety of gases and oils which were condensed in water.
The final substance to be driven off, condensing as a white solid, was phosphorus.
This was a typically alchemical method – alchemists examined the properties of body fluids, hoping to better understand living things in their search for the philosophers’ stone, which they believed offered the prospect of eternal life.
Brand’s method became more widely known in 1737 when an unknown person sold it to the Academy of Sciences in Paris.
Phosphorus was produced by this method until the 1770s when Swedish scientist Carl Wilhelm Scheele – the discoverer of chlorine and one of oxygen‘s independent discoverers – found that phosphorus could be prepared from bone.
The name comes from the Greek word ‘phosphoros’ meaning bringer of light.
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