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.
Discovery of Nitrogen
In 1674 the English physician John Mayow demonstrated that air is not a single element, it is made up of different substances. He did this by showing that only a part of air is combustible. Most of it is not.
Almost a century later, Scottish chemist Joseph Black carried out more detailed work on air. After removing oxygen and carbon dioxide, part of the air remained.
Black used burning phosphorus as the final step in oxygen removal. (Burning phosphorus has a very high affinity for oxygen and is efficient at removing it completely.) Black then assigned further study of the gases in air to his doctoral student, Daniel Rutherford.
Rutherford built on Black’s work and in a series of steps thoroughly removed oxygen and carbon dioxide from air. He showed that, like carbon dioxide, the residual gas could not support combustion or living organisms. Unlike carbon dioxide, however, nitrogen was insoluble in water and alkali solutions. Rutherford reported his discovery in 1772 of ‘noxious air,’ which we now call nitrogen.
Swedish pharmacist Carl Scheele discovered nitrogen independently, calling it spent air.
Scheele absorbed oxygen in a number of ways, including using a mixture of sulfur and iron filings and burning phosphorus. After removing the oxygen, he reported a residual gas which would not support combustion and had between two-thirds and three-quarters of the volume of the original air. Scheele published his results in 1777, although it is thought the work was carried out in 1772.
Although Rutherford and Scheele are now jointly credited with nitrogen’s discovery, it appears to have been discovered earlier by Henry Cavendish, but not published.
Prior to 1772 (the precise date is unknown – Priestley refers to it in his work “Experiments and Observations Made in and Before the Year 1772″) Cavendish wrote to Joseph Priestley describing ‘burnt air’.
The ‘burnt air’ had been prepared by passing air repeatedly over red hot charcoal (removing the oxygen) and then bubbling the remaining gas through a solution of caustic potash (potassium hydroxide) which would have removed the carbon dioxide.
Cavendish wrote: “The specific gravity of this air was found to differ very little from that of common air; of the two, it seemed rather lighter. It extinguished flame, and rendered common air unfit for making bodies burn in the same manner as fixed air, but in a less degree, as a candle which burnt about 80″ in pure common air, and which went out immediately in common air mixed with 6/55 of fixed air, burnt about 26″ in common air mixed with the same portion of this burnt air.”
In 1790 the French chemist Jean-Antoine-Claude Chaptal named the element ‘nitrogen’ after experiments showed it to be a constituent of nitre, as potassium nitrate was called then.
Discovery of Silicon
Quartz (crystalline silicon dioxide) has been known to people for many thousands of years. Flint is a form of quartz, and tools made from flint were in everyday use in the stone age.
In 1789, the French chemist Antoine Lavoisier proposed that a new chemical element could be found in quartz. This new element, he said, must be very abundant. He was right, of course. Silicon accounts for 28% of the weight of Earth’s crust.
It is possible that in England, in 1808, Humphry Davy isolated partly pure silicon for the first time, but he did not realize it.
In 1811, French chemists Joseph L. Gay-Lussac and Louis Jacques Thénard may also have made impure silicon by reacting potassium with silicon tetrafluoride to produce a reddish brown solid which was probably amorphous silicon. They did not, however, attempt to purify this new substance.
In 1824, Swedish chemist Jöns Jakob Berzelius produced a sample of amorphous silicon, a brown solid, by reacting potassium fluorosilicate with potassium and purifying the product with repeated washing. He named the new element silicium.
At that time the concept of semiconductors lay a century in the future. Unaware that such materials existed and that silicon was an excellent example of a semiconductor, scientists debated whether the new element should be classed as a metal or a nonmetal.
Berzelius believed it was a metal, while Humphry Davy thought it was a nonmetal. The problem was that the new element was a better conductor of electricity than nonmetals, but not as good a conductor as a metal.
Silicon was given its name in 1831 by Scottish chemist Thomas Thomson. He retained part of Berzelius’s name, from ‘silicis,’ meaning flint. He changed the element’s ending to on because the element was more similar to nonmetals boron and carbon than it was to metals such as calcium and magnesium. (Silicis, or flint, was probably our first use of silicon dioxide.)
In 1854, Henri Deville produced crystalline silicon for the first time. He did this by electrolyzing an impure melt of sodium aluminum chloride to produce aluminum silicide. The aluminum was removed with water, leaving silicon crystals.
Discovery of Boron
Boron compounds such as borax (sodium tetraborate, Na2B4O7·10H2O) have been known and used by ancient cultures for thousands of years. Borax’s name comes from the Arabic buraq, meaning “white.”
Boron was first partially isolated in 1808 by French chemists Joseph L. Gay-Lussac and L. J. Thénard and independently by Sir Humphry Davy in London. Gay-Lussac & Thénard reacted boric acid with magnesium or sodium to yield boron, a gray solid. They believed it shared characteristics with sulfur and phosphorus and named it bore.
Davy first tried to produce boron by electrolysis of boric acid, but was not satisfied with the results.
He enjoyed greater success reacting boric acid with potassium in a hydrogen atmosphere.
The result was a powdery substance.
Davy commented the substance was, “of the darkest shades of olive. It is opake, very friable, and its powder does not scratch glass.” After carrying out a number of chemical reactions to verify the uniqueness of the substance, Davy wrote, “there is strong reason to consider the boracic basis as metallic in nature, and I venture to propose for it the name of boracium.”
Neither party had, in fact, produced pure boron. Their samples were only about 60% pure.
In 1909, American chemist Ezekiel Weintraub was able to produce 99% pure boron, by reducing boron halides with hydrogen.
Almost a century later, in 2004, Jiuhua Chen and Vladimir L. Solozhenko produced a new form of boron, but were uncertain of its structure.
In 2009, a team led by Artem Oganov was able to demonstrate the new form of boron contains two structures, B12 icosohedra and B2 pairs. Gamma-boron, as it has been called, is almost as hard as diamond and more heat-resistant than diamond.
Talking about boron’s part metal, part non-metal properties, Oganov said, “Boron is a truly schizophrenic element. It’s an element of complete frustration. It doesn’t know what it wants to do. The outcome is something horribly complicated.”
Discovery of Aluminum
People have used alum since ancient times for dyeing, tanning and to stop bleeding. Alum is potassium aluminum sulfate.
In the 1750s German chemist Andreas Marggraf found he could use an alkali solution to precipitate a new substance from alum. Marggraf had previously been the first person to isolate zinc in 1746.
The substance Marggraf obtained from alum was named alumina by French chemist Louis de Morveau in 1760. We now know that alumina is aluminum oxide – chemical formula Al2O3.
De Morveau believed alumina contained a new metallic element, but, like Marggraf, he was unable to extract this metal from its oxide.
In 1807 or 1808, English chemist Humphry Davy decomposed alumina in an electric arc to obtain a metal. The metal was not pure aluminum, but an alloy of aluminum and iron.
Davy called the new metal alumium, then renamed it aluminum.
Aluminum was first isolated in 1825 by Hans Christian Ørsted (Oersted) in Copenhagen, Denmark who reported, “a lump of metal which in color and luster somewhat resembles tin.”
Ørsted produced aluminum by reducing aluminum chloride using a potassium-mercury amalgam. The mercury was removed by heating to leave aluminum.
German chemist Friedrich Wöhler (Woehler) repeated Ørsted’s experiment but found it yielded only potassium metal. Wöhler developed the method further two years later, reacting volatalized aluminum trichloride with potassium to produce small amounts of aluminum. In 1856 Berzelius stated that it was Wöhler who had succeeded in 1827. Wöhler is therefore usually given credit for the discovery.
More recently, Fogh repeated the original experiments and has shown that Ørsted’s method can give satisfactory results.
This has strengthened the priority of Ørsted’s original work and his position as discoverer of aluminum.
For almost three decades, aluminum remained a novelty, expensive to produce and more valuable than gold, until in 1854 Henri Saint-Claire Deville in Paris, France found a way of replacing potassium with much cheaper sodium in the reaction to isolate aluminum. Aluminum then became more popular but, because it was still quite expensive, was used in ornamental rather than practical situations.
Finally, in 1886 American chemist Charles Martin Hall and French chemist Paul Héroult independently invented the Hall-Héroult process, which inexpensively isolates aluminum metal from its oxide electrolytically.
Aluminum is still manufactured using the Hall-Héroult process today.
Discovery of Silver
Silver has been in use since prehistoric times. We do not know who its discoverer was, although the discovery would almost certainly have been of native silver.
Nuggets of native silver metal can be found in minerals and sometimes in rivers; but they are rare. Despite native silver’s rarity, very large pieces of it have been found, such as “pieces of native silver as big as stove lids and cannon balls” found in the early 1900s in Northern Ontario, Canada.
Silver has a special place in the history of the elements because it is one of the first five metals discovered and used by humans. The others were gold, copper, lead and iron.
Silver objects dating from before 4000 BC have been found in Greece and from slightly later in Anatolia (in modern Turkey). Silver artifacts have been found in the Sumerian city of Kish dating from about 3000 BC.
Silver and lead often appear together in nature, for example in the mineral galena which is mainly lead sulfide. Galena actually looks metallic (see image) and would have caught the eyes of people looking for metals.
The silver objects found in Greece, Turkey and Kish were made of silver that was refined from lead-containing ores such as galena. (Humans have been successful chemists for a surprisingly long time.)
First the ore was smelted under reducing conditions to obtain a mixture of silver and lead. The metals then went through cupellation: the metals were heated to about 1000 oC in a strong stream of air. Under these conditions lead reacts with oxygen forming lead oxide, leaving liquid silver metal floating on top.
Our name for the element is derived from the Anglo-Saxon for silver, ‘seolfor,’ which itself comes from ancient Germanic ‘silabar.’
Silver’s chemical symbol, Ag, is an abbreviation of the Latin word for silver, ‘argentum.’ The Latin word originates from argunas, a Sanskrit word meaning shining.
The historical association between silver and money is still found in some languages. The French word for silver is argent, and the same word is used for money. The Romans used the word ‘argentarius’ to mean banker (silver trader).
Discovery of Zinc
Zinc ores have been used to make brass (a mixture of copper and zinc) and other alloys since ancient times.
A zinc alloy comprising 87.5% zinc was discovered in an ancient site in Transylvania.
Zinc smelting began in the 12th century in India by reducing calamine (zinc carbonate, ZnCO3) with wool and other organic materials.
The element name is reported to come from the old German word ‘zinke’ meaning pointed; a reference to the sharp pointed crystals formed after smelting.
Credit for isolating the metal is usually given to Andreas Marggraf in 1746, in Berlin. He heated a mixture of calamine ore and carbon in a closed vessel without copper to produce the metal.
Discovery of Nickel
Nickel is present in metallic meteorites and so has been in use since ancient times.
Artifacts made from metallic meteorites have been found dating from as early as 5000 BC – for example beads in graves in Egypt
Iron is the most abundant element in metallic meteorites, followed by nickel.
It was not until the 1750s that nickel was discovered to be an element.
In the 1600s, a dark red ore, often with a green coating, had been a source of irritation for copper miners in Saxony, Germany. They believed the dark red substance was an ore of copper, but they had been unable to extract any copper from it.
In frustration, they had named it ‘kupfernickel’ which could be translated as ‘goblin’s copper’ because clearly, from the miners’ point of view at any rate, there were goblins or little imps at work, preventing them extracting the copper.
Between 1751 and 1754, the Swedish chemist Axel Cronstedt carried out a number of experiments to determine the true nature of kupfernickel. (We now know that kupfernickel is nickel arsenide, NiAs.)
After finding that its chemical reactions were not what he would have expected from a copper compound, he heated kupfernickel with charcoal to yield a hard, white metal, whose color alone showed it could not be copper. Its properties, including its magnetism, led him to conclude that he had isolated a new metallic element.
Cronstedt named the new element nickel, after the kupfernickel from which he had isolated it.
There is a satisfying symmetry in this discovery. Cronstedt was a pupil of George Brandt, who had discovered cobalt, which sits immediately to the left of nickel in the periodic table.
The names of both elements have their origins in the frustrations of miners caused by metal-arsenic ores: nickel arsenide and cobalt arsenide. Cobalt’s name is derived from the German ‘kobold’ meaning ‘goblin’ – a close relative of the creature from which nickel’s name was derived.
In cobalt’s case, miners mistakenly thought the ore contained silver, and called the ore kobold in frustration at the wicked goblins who they believed were preventing them getting silver from the ore.
In the early twentieth century, Ludwig Mond patented a process using nickel carbonyl to purify nickel. This process is still used today.
Discovery of Cobalt
Since ancient times cobalt compounds have been used to produce blue glass and ceramics.
The element was first isolated by Swedish chemist George Brandt in 1735. He showed it was the presence of the element cobalt that caused the blue color in glass, not bismuth as previously thought.
In about 1741 he wrote, “As there are six kinds of metals, so I have also shown with reliable experiments… that there are also six kinds of half-metals: a new half-metal, namely cobalt regulus in addition to mercury, bismuth, zinc, and the reguluses of antimony and arsenic.”
The word cobalt is derived from the German ‘kobold’, meaning goblin or elf.
Discovery of Iron
Iron has been known since ancient times.
The first iron used by humans is likely to have come from meteorites.
Most objects that fall to earth from space are stony, but a small proportion, such as the one pictured, are ‘iron meteorites’ with iron contents of over 90 percent.
Iron corrodes easily, so iron artifacts from ancient times are much rarer that objects made of silver or gold. This makes it harder to trace the history of iron than the less reactive metals.
Artifacts made from meteorite iron have been found dating from about 5000 BC (and so are about 7000 years old) – for example iron beads in graves in Egypt.
In Mesopotamia (Iraq) there is evidence people were smelting iron around 5000 BC.
Artifacts made of smelted iron have been found dating from about 3000 BC in Egypt and Mesopotamia.
In those times, iron was a ceremonial metal; it was too expensive to be used in everyday life. Assyrian writings tell us that iron was eight times more valuable than gold.
The iron age began about 1300-1200 BC when iron became cheap enough to replace bronze.
Adding carbon to iron to make steel was probably accidental at first – a coming together of molten iron and charcoal from the smelting fire. This probably happened about 1000 BC. Until this happened there were few technological reasons for the bronze age to give way to the iron age; the techniques of improving iron by adding carbon (to make steel) and coldworking were needed before iron would be wholly preferred to bronze.
Iron was used commonly in Roman times. In the first century Pliny the Elder said, “It is by the aid of iron that we construct houses, cleave rocks, and perform so many other useful offices in life.”
The origin of the chemical symbol Fe is from the Latin word ‘ferrum’ meaning iron. The word iron itself comes from ‘iren’ in Anglo-Saxon.
Discovery of Chromium
Chromium was discovered in 1780 by French chemist Nicolas Louis Vauquelin in Paris. He discovered the element in a mineral sample of ‘Siberian red lead’- now known as crocoite (lead chromate).
He boiled the crushed mineral with potassium carbonate to produce lead carbonate and a yellow potassium salt solution of chromic acid.
Vauquelin was convinced by further experiments on the solution that he had found a new metal.
In 1781 he succeeded in isolating the metal. Initially he removed the lead from the mineral sample by precipitation with hydrochloric acid. Vauquelin then obtained the oxide by evaporation and finally isolated chromium by heating the oxide in a charcoal oven.
Vauquelin also identified small amounts of chromium in ruby and emerald stones.
Vauquelin went on to discover Beryllium in 1798.
Chromium was named from the Greek word ‘chroma’, meaning color because it forms a variety of colorful compounds.
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