1. She (go) to Italy five years ago. 2. When he (run) after the tram, he (fall) and (hurt) his leg. We (have) to carry him home. Now he (lie) in bed. The doctor just (leave). 3. He (look) through my album when I (enter). You (like) my photos? I (ask) him. They (be) very good. 4. What you (look) for? I (lose) my pen and (want) to find it. 5. My friend Robert (learn) French for the last three years and now he (study) German, too. 6. They (live) in that town for ten years and then (move) to the country.
Exercise 29. .
Our friend the dog.
Every boy and girl (know) that there (be) hundreds of different animals in the world. And yet, if you asked the question what your favourite animal is, almost every boy and girl (answer) without hesitation,the dog.
All (agree) that the dog (be) the best companion for children. Mr. Dog always (enter) so thoroughly into the games and enjoyment of his little master or mistress. He quickly (understand) what (require) of him.
You (ever/ see) St. Bernard dogs? Many years ago they were named so after a monastery high up in the Alps. After the monks (breed) them, the dogs were used to guide travellers through the snowbound passes. If a traveler (stay) from his pass and (become) lost in the snow drifts, the dogs (rescue) him. The dogs (work) in pairs. When they (find) the traveler who (lie) in the snow, they(try) to dig him out. If the dogs (not/ can/ help) the man, one of them (go) back to the monastery to fetch the monks while the other (remain) with the lost who perhaps (get) some injuries.
Since that time St. Bernard dogs (be) the most intelligent and devoted to their masters.
Exercise 30. Present Simple Present Continuous.
1. ... you that man over there?
a) Do... see b) Are... seeing
2. I'm hungry. I something to eat.
a) am wanting b) want
3. Work very important role in Japan.
a) plays b) is playing
4. It hard now, and the children at home all the time.
a) rains; are staying b) is raining; are staying
5. Can you see who in the park?
a) is sitting b) sits
6. ... you in God?
a) Are... believing b) Do... believe
7. I used to drink coffee but today I tea.
a) am preferring b) prefer
8. She a book now. Dont bother her.
a) reads b) is reading
9. ... she to a political party?
a) Is... belonging b) Does... belong
10. Who is that man? What he ?
a) does... do b) is... doing
ADDITIONAL READING
Chemistry Facts
ü Hydrogen is the first element on the periodic table. It has an atomic number of 1. It is highly flammable and is the most common element found in our universe.
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ü Liquid nitrogen boils at 77 kelvin (−196 C, −321 F).
ü Around 1% of the suns mass is oxygen.
ü Helium is lighter than the air around us so it floats, that's why it is perfect for the balloons you get at parties.
ü Carbon comes in a number of different forms (allotropes), these include diamond, graphite and impure forms such as coal.
ü Under normal conditions, oil and water do not mix. More oil facts.
ü Although it is still debated, it is largely recognized that the word 'chemistry' comes from an Egyptian word meaning 'earth'.
ü The use of various forms of chemistry is believed to go back as long ago as the Ancient Egyptians. By 1000 BC civilizations were using more complex forms of chemistry such as using plants for medicine, extracting metal from ores, fermenting wine and making cosmetics.
ü Things invisible to the human eye can often be seen under UV light, which comes in handy for both scientists and detectives.
ü Humans breathe out carbon dioxide (CO2). Using energy from sunlight, plants convert carbon dioxide into food during a process called photosynthesis.
ü Chemical reactions occur all the time, including through everyday activities such as cooking. Try adding an acid such as vinegar to a base such as baking soda and see what happens!
ü Above 4 C, water expands when heated and contracts when cooled. But between 4 C and 0 C it does the opposite, contracting when heated and expanding when cooled. Stronger hydrogen and oxygen bonds are formed as the water crystallizes into ice. By the time it's frozen it takes up around 9% more space.
ü Often formed under intense pressure over time, a crystal is made up of molecules or atoms that are repeated in a three dimensional repeating pattern. Quartz is a well-known example of a crystal.
ü Athletes at the Olympic Games have to be careful how much coffee they drink. The caffeine in coffee is a banned substance because it can enhance performance. One or two cups are fine but they can go over the limit with more than five. (update - as of 2004 caffeine has been taken back off the WADA banned list but its use will be closely monitored to prevent future abuse by athletes.)
Diamond Facts
Diamond is an allotrope (different form) of carbon.
The word diamond comes from the Greek word meaning unbreakable.
The carbon atoms in diamonds are arranged in a strong, tetrahedral structure.
Diamond is the hardest natural material known and is often used for industrial cutting and polishing tools.
Diamond has a hardness of 10 on Mohs scale of mineral hardness, with 1 being the softest (talc) and 10 being the hardest.
Diamond is the best known thermal conductor (heat transfer) among naturally occurring substances.
Under the normal pressures and temperatures we experience on the Earths surface, diamonds are actually thermodynamically unstable, slowly transforming into graphite. Yes, you read that correctly, diamonds are indeed turning into graphite, but thankfully for all those diamond owners out there its a process that is far too slow for humans to notice.
Most of the Earths natural diamond deposits are found in Africa.
Around 26,000 kilograms (57,000 lb) of diamonds are mined around the world every year. They are worth billions of dollars to the powerful companies that control their production.
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Diamonds have often been a source of conflict and controversy, the term blood diamond refers to a diamond mined in an unstable area and sold to finance war. This issue was brought to public attention in the 2006 movie named Blood Diamond (starring Leonardo DiCaprio and Jennifer Connelly).
Diamond is the worlds most popular and sought after gemstone. They are frequently worn as part of jewelry such as rings and necklaces. As well as their rarity, they are also well suited to jewelry because they polish well and can only be scratched by other diamonds.
Diamonds are cut with considerable precision to optimize the luster and attention gathering shine of each specific diamond.
Diamonds are valued according to their cut, color, carat and clarity.
Calcium Facts
v Calcium is found in many rocks such as limestone, chalk and marble as well as many dairy products and vegetables. Read on for more interesting facts about calcium's various properties and uses.
v Calcium is a chemical element with the symbol Ca and an atomic number of 20.
v The name calcium comes from the Latin word calx which means lime.
v Of all elements in the Earth's crust Calcium is the 5th most abundant. It makes up just over 3% of soil, air and oceans.
v Calcium is not naturally found in its elemental state but calcium compounds are common.
v Calcium compounds are most commonly found in sedimentary rocks such as limestone, chalk and marble where calcium carbonate minerals such as calcite and dolomite are present. Check out our calcium carbonate facts for more information.
v Calcium is also found in other minerals such as gypsum (calcium sulfate) and fluorite (calcium fluoride) and it occurs to a lesser extent in igneous and metamorphic rocks, mainly in silicate minerals.
v The element must be extracted using electrolysis. Once purified into a soft silvery-white metal calcium is reactive, it will rapidly form a gray-white oxide and nitride coating when exposed to air.
v Pure calcium metal reacts quite vigorously with water generating hydrogen gas.
v In powdered form, the reaction with water is extremely rapid and quite violent as the increased surface area of the powder accelerates the reaction.
v In the first century the Romans were preparing lime as calcium oxide but they did not recognize it as a metal.
v Calcium was not isolated as a metal until 1808 when Englishman Sir Humphry Davy electrolyzed a mixture of lime and mercuric oxide. Swedish chemists Berzelius and Pontin had created an amalgam of calcium by electrolyzing lime in mercury. Using their amalgam idea, Davy managed to isolate pure calcium metal.
v Calcium has a melting point of 1,548 F (842 C) and a boiling point of 2,703 F (1,484 C).
v Calcium is found in the human body as calcium ions, it is not present in its element form. It is the 5th most abundant element in our bodies. About one third of the mass of the human body is calcium after all water is removed.
v Calcium is very important for the human body. 99% of the body's calcium is stored in the bones and teeth, helping to strengthen them. The other 1% helps with muscle movement allowing nerves to carry messages between the brain and our body parts. It helps blood vessels move blood around and assists with the release of hormones and enzymes.
v We mainly get our body's calcium requirements through food. Vitamin D is needed to absorb this calcium. As a mineral, calcium is found in many foods, especially in dairy products such as milk, yogurt, and cheese. Vegetables like as broccoli, kale, and spinach are also high in calcium.
v Calcium compounds are used in the making of cement, glass, lime, bricks, paint, paper, sugar, removing non-metallic impurities from alloys, and as a reduction agent in the preparation of other metals.
v Calcium salts are used to produce a deep orange color in fireworks.
Oxygen Facts
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o Oxygen is an element with the chemical symbol O and atomic number 8.
o Oxygen is a very reactive element that easily forms compounds such as oxides.
o Under standard temperature and pressure conditions two oxygen atoms join to form dioxygen (O2), a colorless, tasteless and odorless gas.
o Oxygen is essential to human life, it is found in the air we breathe and the water we drink (H20).
o Oxygen makes up around 21% of the air you breathe. It is also the most common element in the Earths crust (around 47%) and the third most common element in the Universe (but far less than hydrogen and helium, the two most common).
o The large amount of oxygen on Earth is supported by the oxygen cycle which involves the movement of oxygen between the air, living things and the Earths crust. Photosynthesis (a process that converts carbon dioxide into organic compounds using sunlight) plays a major role in this cycle.
o Ozone (O3) is an allotrope (different form) of oxygen that combines three oxygen atoms together. While ground level ozone is an air pollutant, the ozone layer in the Earths upper atmosphere provides protection from the suns harmful rays by filtering UV light.
o The suns mass is made up of around 1% oxygen.
o Between 1770 and 1780, Swedish pharmacist Carl Wilhelm Scheele, British clergyman Joseph Priestley and French chemist Antoine Laurent Lavoisier researched, documented and helped discover oxygen. The name oxygen was first used by Lavoisier in 1777.
o Oxygen therapy is used as a common medical treatment. You may have seen patients on TV or in real life using an oxygen mask or nasal cannula (a plastic tube that fits behind the ears and delivers oxygen through the nostrils).
o Oxygen has a number of other practical uses such as smelting metal from ore, water treatment, as an oxidizer for rocket fuel and a number of other industrial, chemical and scientific applications.
o Concentrated oxygen promotes fast combustion. While a spark or heat is still needed to start a fire, having concentrated oxygen near various fuels can be very dangerous.
Nitrogen Facts
Ø Nitrogen is a chemical element with the symbol N and atomic number of 7.
Ø Under normal conditions nitrogen is a colorless, odorless and tasteless gas.
Ø Nitrogen makes up around 78% of the air you breathe.
Ø Nitrogen is present in all living things, including the human body and plants.
Ø Nitrogen gas is used in food storage to keep packaged or bulk foods fresh. It is also used in the making of electronic parts, for industrial purposes and has many other useful applications.
Ø Nitrogen gas is often used as an alternative to carbon dioxide for storing beer in pressurized kegs. The smaller bubbles it produces is preferred for some types of beer.
Ø Titan, the largest moon of Saturn, has an atmosphere nearly entirely made of nitrogen (over 98%). It is the only moon in our solar system known to have a dense atmosphere.
Ø Nitrogen is in a liquid state when at a very low temperature. Liquid nitrogen boils at 77 kelvin (−196 C, −321 F). It is easily transported and has many useful applications including storing items at cold temperatures, in the field of cryogenics (how materials behave at very low temperatures), as a computer coolant (a fluid used to prevent overheating), removing warts and much more.
Ø Decompression sickness (also known as the bends) involves nitrogen bubbles forming in the bloodstream and other important areas of the body when people depressurize too quickly from scuba diving. Similar situations can occur for astronauts and those working in unpressurized aircraft.
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Ø Nitrous oxide (also known as laughing gas or by its chemical formula N2O) is used in hospitals and dental clinics as an anesthetic (removing or reducing pain and general awareness for various surgeries).
Ø Nitrous oxide is also used in motor racing to increase the power of engine and speed of the vehicle. When used for this purpose it is often referred to as nitrous or NOS.
Ø Nitrous oxide is a considerable greenhouse gas and air pollutant. By weight is has nearly 300 times more impact than carbon dioxide.
Ø Nitroglycerin is a liquid used to create explosives such as dynamite. It is often used in the demolition and construction industries as well as by the military.
Ø Nitric acid (HNO3) is a strong acid often used in the production of fertilizers.
Ø Ammonia (NH3) is another nitrogen compound commonly used in fertilizers.
Hydrogen Facts
The chemical symbol of hydrogen is H. It is an element with atomic number 1, this means that 1 proton is found in the nucleus of hydrogen.
Hydrogen is the lightest, simplest and most commonly found chemical element in the Universe, making up around 75% of its elemental mass.
Hydrogen is found in large amounts in giant gas planets and stars, it plays a key role in powering stars through fusion reactions.
Hydrogen is one of two important elements found in water (H2O). Each molecule of water is made up of two hydrogen atoms bonded to one oxygen atom.
In 1766, during an acid metal reaction, Henry Cavendish first formally recognized hydrogen. In 1781 he also found that hydrogen produces water when burned. While Cavendish is usually given credit for the discovery of hydrogen as an element, it had been produced by earlier scientists who were unaware of hydrogen as a unique chemical element.
It wasnt until a few years later (1783) that hydrogen was given its name. The word hydrogen comes from the Greek word hydro (meaning water) and genes (meaning creator).
Hydrogen gas has the molecular formula H2. At room temperature and under standard pressure conditions, hydrogen is a gas that is tasteless, odorless and colorless.
Hydrogen can exist as a liquid under high pressure and an extremely low temperature of 20.28 kelvin (−252.87C, −423.17 F). Hydrogen is often stored in this way as liquid hydrogen takes up less space than hydrogen in its normal gas form. Liquid hydrogen is also used as a rocket fuel.
Under extreme compression hydrogen can also make a transition to a state known as metallic hydrogen. Laboratory research into this area is ongoing as scientists continue efforts to produce metallic hydrogen at low temperature and static compression.
Hydrogen is used to power a range of new alternate fuel vehicles. The chemical energy of hydrogen is converted by a combustion method similar to current engines or in a fuel cell which produces water and electricity by reacting hydrogen with oxygen.
Engineers and car manufacturers are researching the possibility of using hydrogen gas as an efficient and viable car fuel. One of the possibilities involves storing hydrogen as a solid state in car fuel tanks. While there are many challenges involved in this process it would allow for greater hydrogen storage in vehicles, allowing them to travel for longer before refueling.
Hydrogen peroxide is a chemical compound with the molecular formula H2O2. It is often used as a hair bleach or cleaner. At certain concentrations it can also be used to clean wounds.
Hydrogen was used for air travel from 1852 when the first hydrogen lifted airship was created by Henri Giffard. Later airships that used hydrogen were called zeppelins and while they were reliable and safe for the majority of the time their use was stopped soon after the Hindenburg disaster in 1937. The Hindenburg airship was destroyed in a midair fire over New Jersey that was both filmed and broadcast live on radio.
Hydrogen is commonly used in the petroleum and chemical industries and is also widely used for many physics and engineering applications such as welding or as a coolant.
Hydrogen can be potentially dangerous to humans due to fires that can start when it is mixed with air, our inability to breathe it in its pure oxygen free form and also in its extremely cold liquid state.
Oil Facts
Oil is a liquid at room temperature.
Under normal circumstances, oil does not mix with water.
A substance that allows oil and water to mix is called an emulsifier, a good example of this is detergent. Check out our oil and water mixing experiment for more.
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Vegetable oils are made from plants, examples include sunflower oil, coconut oil, corn oil, peanut oil and palm oil.
Some oils are used in cooking, such as olive oil.
Crude oil (petroleum) is a thick, black liquid found underground.
Crude oil comes from fossilized organic material such as plants and animals.
Oil has a wide variety of uses and is often used in cosmetics, medicine, paint, lubricants and as a fuel.
Crude oil is converted at oil refineries into a range of different fuels including gasoline (petrol), diesel, kerosene, jet fuel, liquefied petroleum gas (LPG) and more.
Fuels such as gasoline, diesel and jet fuel are used to help power engines in machines and vehicles such as cars, trucks and airplanes.
Artificially made synthetic oils are used in certain situations where their unique properties are advantageous, for example synthetic oils respond better to extreme temperatures and are used as lubricants in the jet engines of aircraft.
Carbon Facts
ü Carbon is a chemical element with the symbol C and atomic number 6.
ü The word carbon comes from the Latin word carbo, meaning coal.
ü Carbon forms a large number of compounds, more than any other element. Because of its willingness to bond to other nonmetallic elements it is often referred to as the building block of life.
ü While carbon forms many different compounds it is a relatively unreactive element.
ü There are several allotropes (different forms) of carbon with the three most well known being amorphous carbon (coal, soot etc), diamond and graphite.
ü The properties of diamond and graphite are very different with diamond being transparent and very hard while graphite is black and soft (soft enough to write on paper).
ü Graphite is used for its thermal insulation (lower rate of heat transfer) properties. It is also a very good conductor or electricity.
ü The carbon atoms in graphite are bonded in flat hexagonal lattices and layered in sheets.
ü Carbon is the 4th most common element in the Universe (after hydrogen, helium and oxygen). It is the 15th most common element in the Earths crust while it is the second most common element in the human body (behind oxygen).
ü Carbon has the highest melting point of all elements, around 3500 C (3773 K, 6332 F).
ü Hydrocarbons are organic compounds made entirely of molecules featuring just hydrogen and carbon. Organic chemistry involves the study of hydrocarbons.
ü The simplest hydrocarbon compound is methane (CH4).
ü Carbon was discovered by early human civilizations in the form charcoal and soot.
ü The term carbon footprint refers to the amount of greenhouse gas emissions caused by a country, organization or individual person.
ü The carbon cycle is the process in which carbon is exchanged between all parts of Earth and its living organisms. It is of vital importance to life on Earth, allowing carbon to be continually reused and recycled.
ü Carbon is found in the Earths atmosphere in the form of carbon dioxide (CO2). Although it only makes up a small percentage of the atmosphere it plays an important role, including being used by plants during photosynthesis.
ü Carbon monoxide (CO) is very toxic to both humans and animals. It forms in conditions when there is not enough oxygen to form carbon dioxide (CO2). In many countries around the world, carbon monoxide poisoning is the most common kind of fatal poisoning.
ü Carbon fiber is a strong material that consists of thin fibers made up largely of carbon atoms which are bonded together in microscopic crystals. It is very useful for applications needing high strength and low eight.
ü Fossil fuels such as methane gas and crude oil (petrol) play a large role in modern economies.
ü Plastics are made from carbon polymers. Carbon is used to form alloys with iron such as carbon steel.
ü Graphite and clay are combined to make the lead used in pencils.
ü Charcoal is commonly used for grilling food on barbeques.
Coal Facts
v Coal is made largely of carbon but also features other elements such as hydrogen, oxygen, sulfur and nitrogen.
v Coal starts off as plant matter at the bottom of water. It is eventually covered and deeply buried by sediments where over time metamorphosis (a change in form) takes place.
v Different types of coal contain different amounts of carbon. Lignite contains only around 60 to 75%, while anthracite contains more than 92%.
v Anthracite is a hard, shiny, black coal that burns with a blue, smokeless flame. While most forms of coal are associated with sedimentary rock, anthracite undergoes metamorphism and is linked to metamorphic rocks.
v Coal has long been burned to create electricity and heat. The use of coal is increasing every year, in 2006 the world consumed over 6,000,000,000,000 kilograms of coal!
v Coal is the worlds largest source of energy for the production of electricity.
v Coal is converted to electricity by being burned in a furnace with a boiler. The boiler water is heated until it becomes steam, with the steam then spinning turbines and generators to create the electricity.
v Nearly 70% of Chinas electricity comes from coal. In total, coal produces around 40% of the worlds electricity.
v Coal mining and the subsequent burning of coal can have many bad effects on both humans and the environment. Examples of this include waste products, acid rain, contaminated water, poisonous emissions, high levels of carbon dioxide and increased risks of lung cancer for coal plant workers.
v A popular saying among many cultures is that if you behave badly during the year, Santa will deliver you a lump of coal for Christmas.
Silicon Facts
Ø The chemical element Silicon has a symbol Si and atomic number 14.
Ø Silicon is a metalloid (or semimetal). This means it has some properties like a metal, for example, it looks like a metal and some like a non-metal, for example, it does not do conduct electricity very easily.
Ø Because silicon is a metalloid it is useful as a semiconductor which means it has electrical conductivity between metals and non-metal insulators like glass.
Ø Silicon is the 8th most abundant element in the universe by mass.
Ø Silicon is not found as a free element in nature, but rather it occurs as oxides and silicates in many minerals. Over 90% of the Earth's crust (about 28% by mass) is composed of silicate minerals, which is why silicon is the 2nd most common element on earth after oxygen.
Ø Sand is a compound of silicon known as silicon dioxide (silica) and of course glass is made by heating sand to a very high temperature.
Ø Some silicate minerals of interest include granite, asbestos, hornblende, feldspar, clay and mica.
Ø Certain types of meteorites called aerolites are predominately made of silicon.
Ø At room temperature Silicon is a solid its melting point is 2,577 F (1,414 C) and its boiling point is 5,909 F (3,265 C).
Ø Gay Lussac and Louis Jacques Thénard discovered an impure form of silicon in 1811. But Jöns Jacob Berzelius is credited with the discovery of silicon in 1824.
Ø People exposed to breathing in large amounts of silicon compounds such as miners and stonecutters have a high risk of developing a serious lung disease known as silicosis.
Ø Even though silicon is widely found as silicates very few living organisms have a need for it. Some form of ocean sponges have a silica structure in their skeletons and some plants like rice require silicon for growth.
Ø Elemental silicon has had a large impact on today's world economy. Most free silicon is used for steel refining, aluminum-casting, and in chemical industries. But it is the small portion (less than 10%) of highly purified silicon used in semiconductor electronics that is most critical for today's computer technology and electronic industries.
Ø Silicon's use as an important part of computer semiconductors and high-technology devices has seen its name used around the world as a nickname for areas that contain a number of technology-related companies and industries. The original being Silicon Valley in California, but there are over 10 other areas that have silicon in their name for example 'Silicon Roundabout' in North London.
Neon Facts
o Neon is a chemical element with the symbol Ne and atomic number 10.
o The name neon comes from the Greek word νέον meaning new.
o Neon is a colorless, odorless inert (not chemically reactive) gas. It is in a group called 'noble gases' in the periodic table.
o Neon has about two-thirds the density of air and is the second lightest noble gas after helium.
o Neon was discovered by British chemists Sir William Ramsay and Morris W. Travers in 1898. The pair were studying liquid air by chilling a sample of air until it became a liquid, then warming the liquid up and collecting the gases as they boiled off. Neon was the second of three new gases to be discovered by the pair the first being krypton and the third xenon.
o Neon has no true chemical compounds, meaning it forms no compounds to fix it to solids or join with other elements.
o The melting point of neon is -433.46 F (-258.59 C) and the boiling point is -410.94 F (-246.08 C).
o Neon is the fifth most abundant chemical element in the universe after hydrogen, helium, oxygen, and carbon. It is however, a rare gas in Earth's atmosphere, making up just 0.0018%.
o Stable isotope forms of neon are produced within stars.
o Neon gas emits a brilliant red-orange color when charged with electricity.
o In 1902, a French engineer Georges Claude began creating neon lighting with the surplus neon leftover from his air liquefaction company. He tried using neon tubes for indoor lighting, but the color put homeowners off. So instead, in 1912, his company began selling neon discharge tubes as advertising signs.
o Neon advertising signage was a success and in 1923 the concept was introduced to the U.S. when two large neon signs were put up by a Los Angeles Packard car dealership.
o While neon accounts for the bright reddish-orange light in advertising signs all other colors are generated by other noble gases or by colors of fluorescent lighting, yet they are still referred to as neon signs.
o Today, neon has uses in vacuum tubes, high-voltage indicators, lightning arrestors, wave meter tubes, television tubes, plasma tubes and helium-neon lasers.
o Liquid neon is also now commercially available and is used as a cryogenic refrigerant.
o Because neon is quite rare in our atmosphere both neon gas and liquid neon are relatively expensive costing more than 55 times that of liquid helium.
o If a balloon is filled with neon it will rise in the air but do so at a much slower rate than a balloon filled with helium.
Chlorine Facts
v The chemical element Chlorine has the symbol Cl and atomic number 17.
v On the periodic table Chlorine is in the halogen group and it is the 2nd lightest halogen gas after fluorine.
v In its standard form chlorine is a yellow-green gas, but its common compounds are usually colorless. Chlorine has a strong distinctive odor such as the smell of household bleach.
v The name Chlorine is from the Greek word chloros which means greenish yellow.
v Chlorine has a melting point of -150.7 F (-101.5 C) and a boiling point of -29.27 F (-34.04 C).
v Free chlorine is rare on Earth. Chlorine combines with nearly all elements to create chlorine compounds called chlorides, which are much more common.
v There are over 2000 naturally occurring organic chlorine compounds.
v The most common compound of chlorine has been known about since ancient times, it is sodium chloride we know it better as 'common salt'.
v Swedish chemist, Carl Wilhelm Scheele, discovered Chlorine in 1774 believing it contained oxygen. In 1810, Sir Humphry Davy tried the same experiment and concluded that Chlorine was in fact an element, and not a compound.
v Chlorine is the 3rd most abundant element in Earth's oceans (about 1.9% of the mass of seawater is chloride ions) and the 21st most common chemical element in the Earth's crust.
v Chlorine's high oxidizing properties saw it used to purify water in the U.S as early as 1918. Today chlorine and its various compounds are used in most swimming pools throughout the world to keep them clean and in many household cleaning products such as disinfectants and bleaches.
v Chlorine is also used in a range of other industrial and consumer products such as the making of plastics, whitening of textiles, pharmaceuticals, in chloroform, insecticides, paper products, solvents, dyestuffs and paints.
v In high concentrations chlorine is extremely dangerous and poisonous. It is also heavier than air, so can fill up enclosed spaces. Because of these facts chlorine was the first gaseous chemical used as a weapon in warfare when both sides at times dispersed it in low-lying foxholes and trenches of World War I.
Helium Facts
Helium is a chemical element with the symbol He and atomic number 2.
Helium is a colorless, tasteless and odorless gas.
Helium is the second most common element in the Universe (after hydrogen), making up around 24% of its mass.
Helium is part of a group of chemical elements called noble gases, the other five that occur naturally are neon, argon, krypton, xenon and radon. Under normal conditions they share similar properties, including being less likely to participate in chemical reactions due to their outer shell of electrons being full. Helium is the second least reactive element after neon.
French and English astronomers Pierre Janssen and Norman Lockyer are jointly credited with discovering helium after spectral analysis of sunlight following a solar eclipse in 1868.
The word helium comes from the Greek word meaning sun (helios). It was named by Lockyer and English chemist Edward Frankland.
The USA is the worlds largest supplier of helium, with many reserves found in large natural gas fields.
The rate at which helium is currently being used by humans is much faster than the rate at which the reserves are being replenished. New technologies for obtaining or recycling helium are one way for gas companies to help slow this problem.
Because helium is lighter than air it is commonly used to fill airships, blimps and balloons. As it doesnt burn or react with other chemicals, helium is relatively safe to use for this purpose.
While hydrogen is 7% more buoyant than helium it has a much higher fire risk.
You might notice the helium balloon you got from the amusement park slowly falling to the ground after a few days, this happens as the helium gradually leaks from the balloon.
Helium has a lifting force of around one gram per liter. A balloon that holds 10 liters of helium should therefore lift an object weighing 10 grams. Unfortunately youll need around 5000 of these balloons if you weigh around 50kgs and want to get off the ground.
The balloon boy hoax from October 15, 2009 led people to believe that a six year old boy had floated away in a home made helium balloon when in fact he was hiding at his house the whole time.
Because helium is less dense than normal air, when inhaled from a source such as a helium balloon it briefly changes the sound of a persons voice, making it much sound much higher. However, breathing in too much helium can be very dangerous, potentially choking people due to a lack of oxygen.
Helium can be in a liquid and even solid state but they can only occur at temperatures near absolute zero.
Liquid helium is used to cool metals for superconductivity use. The European Organization for Nuclear Researchs (CERN) Large Hadron Collider uses liquid helium to maintain an extremely low temperature.
Helium is often used in space programs, displacing fuel in storage tanks and having other rocket fuel applications.
Radon Facts
o Being one of the heaviest gases, radon tends to accumulate in low lying areas such as house basements, but is a gas that is very hard to detect.
o Radon is a chemical element, its symbol is Rn and it has an atomic number of 86.
o Radon is a radioactive noble gas, it is colorless, odorless and tasteless.
o When radon is cooled below its freezing point of −96 F (−71 C) it emits a bright radiating luminescence that starts out yellow and as the temperature lowers becomes a orangey red color.
o Radon has a melting point of -95 F (-71 C) and a boiling point of -79 F (-61.7 C).
o Under normal conditions radon is one of the densest and is the heaviest of known gases.
o The radioactive health risk of radon and the fact it costs a lot has made it hard for experimental chemical research to be performed. Therefore very few radon compounds have been found.
o In 1900, German physicist Friedrich Ernst Dorn discovered radon when he found that radium compounds emit a radioactive gas which he called Radium Emanation. In 1908, William Ramsay and Robert Whytlaw Gray isolated radon and figured out its density.
o The naturally occurring decay of the two most common radioactive elements uranium and thorium, produces radium. Decay of radium then produces radon. As radon decays, it produces more radioactive elements called radon daughters or decay products.
o Radon gas and its decay particles can reach very high concentrations inside buildings. This is especially true in lower levels such as basements due to the heaviness of the gas. Thus, radon is considered a significant contaminant to indoor air quality.
o There is a clear link between breathing high concentrations of radon and incidence of lung cancer. After smoking, radon is the 2nd most frequent cause of lung cancer with over 21,000 lung cancer deaths per year in the US alone.
o In the 1940s and 50s very little ventilation in mines meant incidents of lung cancer due to radon exposure was high among miners of uranium and other hard rock materials, especially in the Czech Republic and U.S. This lead to an overhaul of mining ventilation systems around the world.
o Radon naturally occurs in some hot springs and other spring waters.
Sulfur (Sulphur) Facts
Sulfur (also spelt sulphur) in its element form is found in volcanic and hot spring areas and is usually a yellow color.
Sulfur or sulphur is a chemical element with symbol S and atomic number 16.
The element has traditionally been spelt 'sulphur' in the United Kingdom and most of the Commonwealth countries, while the United States used 'sulfur'. The term sulfur is now the standard name used in most contexts.
Because sulfur is so abundant in its native form the element has been known since ancient times. The Bible refers to sulfur as brimstone meaning 'burn stone' or 'stone that burns'. There have also been recorded uses of sulfur in ancient India, Greece, China and Egypt.
Elemental sulfur has a bright yellow color at room temperature and is a non-metal flaky crystalline solid. When burned, sulfur melts to a blood-red liquid and burns a bright blue.
In 1777, French chemist Antoine Lavoisier managed to convince the scientific community that sulfur was not a compound but in fact a basic element.
The melting point of sulfur is 247.3 F (119.6 C) and the boiling point is 832.3 F (444.6 C).
Sulfur is non-toxic in its pure element form and in the sulphate form. But its compounds such as carbon disulphide, hydrogen sulphide and sulfur dioxide are all toxic.
Mineral collectors like elemental sulfur crystals for their distinct, brightly colored polyhedron (multisided) shapes.
Sulfur compounds can naturally occur as sulfide minerals such as pyrite, cinnabar, galena, sphalerite and stibnite. Or as sulfate minerals such as gypsum, alunite and barite.
Pure elemental sulfur is found near hot springs/pools and volcanic areas, most notably in countries around the Pacific Ring of Fire such as Indonesia, Chile, and Japan where these deposits are often mined.
The pungent smell referred to as "sulfur" that is very distinctive in volcanic areas comes mainly from the compound hydrogen sulfide. In fact hydrogen sulfide and other sulfur forms produced by living organisms are responsible for the awful smell from skunks, rotton eggs and burning hair or feathers.
Sulfur is an essential element of all living forms. It is one of the top 8 most abundant elements in the human body. For example, a person weighing 70 kg's has about 140 grams of sulfur in them.
Sulfur is used commercially in fertilizers, in the manufacture of sulfuric acid (one of the most important industrial chemicals), in matches and traditionally in black gunpowder. 'Dusting sulfur' (powdered elemental sulfur) is used in pesticides, insecticides and fungicides and sprayed over fruit and vegetable crops.
Many meteorites contain sulfide compounds and Jupiter's volcanic moon Io has colorful areas formed by molten, solid and gaseous sulfur.
The burning of fossil fuels such as coal and oil produces sulfur dioxide which is largely responsible for incidents of acid rain that have been known to occur near industrial areas.
