Minggu, 30 Mei 2010


99% of the mass of the human body is made up of only six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Every organic molecule contains carbon. Since 65-90% of each body cell consists of water (by weight), it isn't surprising that oxygen and hydrogen are major components of the body.

Here's is a look at the major elements in the body and what these elements do.

1. Oxygen is necessary for respiration. You will find this element in the lungs, since about 20% of the air you breathe is oxygen.

2. Carbon is ingested in food that is eaten and breathed in as a component of air. It is found in the lungs as a waste product of respiration, carbon dioxide.

3. Hydrogen is a component of the water molecules in the body, as well as most other compounds.

4. Nitrogen gas is found in the lungs, since most of the air you breathe consists of this element. Nitrogen is a component of proteins, nucleic acids, and other organic compounds.

5. Calcium is also found in the nervous system, muscles, and the blood where it is integral in proper membrane function, conducting nerve impulses, regulating muscle contractions, and blood clotting.

6. Phosphorus is part of nucleic acids, energy compounds, and phosphate buffers. The element is incorporated into the bones, combines with other elements including iron, potassium, sodium, magnesium and calcium. It is necessary for sexual function and reproduction, muscle growth, and to supply nutrients to the nerves.

7. Potassium is important for membrane function, nerve impulses, and muscle contractions. Potassium cations are found in cellular cytoplasm. The electrolyte helps to attract oxygen and remove toxins from the tissues.

8. Sodium is important for proper nerve and muscle function. It is excreted in perspiration.

9. Chlorine is a part of hydrochloric acid, used to digest food. It is involved in proper cell membrane function.

10. Magnesium is needed for strong teeth and bones.

11. Sulfur is a component of many amino acids and proteins.

Sabtu, 29 Mei 2010


Periodic Table

The first periodic table was devised by Dmitri Mendeleev and published in 1869.

Mendeleev found he could arrange the 65 elements that were then known in a grid or table so that each element had:

1. A higher atomic weight than the one on its left.

2. Similar chemical properties to other elements in the same column.

He realized that the table in front of him lay at the very heart of chemistry. In his table he noted gaps - spaces where elements should be but none had yet been discovered.

In fact, just as Adams and Le Verrier could be said to have discovered the planet Neptune on paper, Mendeleev could be said to have discovered germanium (which he called eka-silicon because he observed a gap between silicon and tin), gallium (eka-aluminum) and scandium (eka-boron) on paper, for he predicted their existence and their properties before their actual discoveries.

Although Mendeleev had made a crucial breakthrough, he made little further progress because the Rutherford-Bohr model of the atom had not yet been formulated.

In 1913, Henry Moseley, who worked with Rutherford, showed it is atomic number (charge) and not (as Mendeleev had proposed) atomic weight that is most fundamental to the chemical properties of any element. Like Mendeleev, Moseley was able to predict correctly the existence of new elements based on his work.

And today the elements are still arranged in order of increasing atomic number (Z) as you go from left to right across the table. We call the horizontal rows periods and the vertical rows groups.

We also know an element's chemistry is determined by the way its electrons are arranged - its electron configuration.

The noble gases are found in group 18, on the far right of each period. The reluctance of the noble gases to undergo chemical reactions indicates that the atoms of these gases strongly prefer their own electron configurations - featuring a full outer shell of electrons - to any other.

In contrast to the noble gases, the elements with the highest reactivity are those with the greatest need to gain or lose electrons in order to achieve a full outer shell of electrons.

Elements sitting in the same group (e.g. the alkali metals in Group 1) all have the same number of outer electrons, leading to similar chemical properties.

Likewise the halogens in Group 17 also have similar properties to one another. When halogens react, they gain an electron to form negatively charged ions. Each ion has the same electron configuration as the noble gas in the same period. The ions are therefore more chemically stable than the elements from which they formed.

There is a progression from metals to non-metals across each period.

The block of elements in groups 3 - 12 contains the transition metals. These are similar to one another in many ways; they produce colored compounds, have variable valency and are often used as catalysts. The rare earth elements can be divided into lanthanides (elements 58 - 71) and actinides (elements 90 - 103). The naturally occurring rare earths are found on earth in only very small amounts. The actinides include most of the well-known elements that take part in or are produced by nuclear reactions. No element with atomic number higher than 92 occurs naturally. These elements are produced artificially in nuclear reactors or particle accelerators.



* 1 quart milk (any kind)
* 1/4 to 1/2 cup non-fat dry milk (optional)
* 2 tablespoons existing yogurt with live cultures (or you can use freeze-dried bacteria instead)


1. Heat milk to 185F (85C). Using two pots that fit inside one another, create a double boiler or water jacket effect. This will prevent your milk from burning, and you should only have to stir it occasionally. If you cannot do this, and must heat the milk directly, be sure to monitor it constantly, stirring all the while. If you do not have a thermometer, 185F (85C) is the temperature at which milk starts to froth.

2. Cool the milk to 110F(43C). The best way to achieve this is with a cold water bath. This will quickly and evenly lower the temperature, and requires only occasional stirring. If cooling at room temperature or in the refrigerator, you must stir more frequently. Don't proceed until the milk is below 120F(49C), and don't allow it to go below 90F (32C). 110F (43C) is optimal.

3. Warm the starter. Let the starter yogurt sit at room temperature while you are waiting for the milk to cool. This will prevent it from being too cold when you add it in.

4. Add nonfat dry milk, if desired. Adding about 1/4 cup to 1/2 cup nonfat dry milk at this time will increase the nutritional content of the yogurt. The yogurt will also thicken more easily. This is especially helpful if you are using nonfat milk.

5. Add the starter. Add 2 tablespoons of the existing yogurt, or add the freeze-dried bacteria.

6.Put the mixture in containers. Pour your milk into a clean container or containers. Cover each one tightly with a lid or plastic wrap.

7.Allow the yogurt bacteria to incubate. Keep the yogurt warm and still to encourage bacteria growth, while keeping the temperature as close to 100F (38C) as possible. An oven with a pilot light is one option; see Tips for others. After seven hours you will have a custard-like texture, a cheesy odor, and possible some greenish liquid on top. This is exactly what you want. The longer you let it sit beyond seven hours, the thicker and more tangy it will become.

8.Refrigerate the yogurt. Place the yogurt in your fridge for several hours before serving. It will keep for 1-2 weeks. If you are going to use some of it as starter, use it within 5-7 days, so that the bacteria still have growing power. Whey, a thin yellow liquid, will form on the top. You can pour it off or stir it in before eating your yogurt.

9.Add optional flavorings. Experiment until you develop a flavor that your taste buds fancy.

10.Use yogurt from this batch as starter for the next batch.


Have you ever wondered what makes certain things glow under black lights?

For this experiment you will need:

• a black light
• petroleum jelly
• a piece of paper

First we’ll use the petroleum jelly as a kind of invisible ink. Dip your finger into the jelly, then use your finger to write a message on the piece of paper. Use more jelly if you need to – but this probably isn’t the time to write a long speech! When you’re finished, wipe any remaining jelly off your finger. Have the black light ready, then turn off the room lights and turn on the black light.

Can you see the message? Why is something that you couldn’t see in room light now visible when you can’t see any light?

First, let’s talk about the light. The reason black lights are called "black lights" is because they give off very little light that our eyes can see. Visible light contains a spectrum of colors ranging from red, through orange, yellow, green, and blue, to violet or purple. Beyond violet light in the spectrum is ultraviolet light, which our eyes cannot detect.

You may have heard of ultraviolet light if you know about sunburn. Sunburn is caused by a type of ultraviolet light, which scientists call “ultraviolet B” (UV-B). UV-B is higher in energy than the light from black lights, which is called “ultraviolet A” (UV-A). Black lights will not give you a sunburn.

If we can't see ultraviolet light, why does the petroleum jelly glow under the black light?

Most of the time when we look at an object, we see light reflected from the surface of the object. But with a black light, there isn't much visible light, so simple reflection of light doesn't account for how bright the jelly glows. Petroleum jelly contains substances called phosphors. A phosphor absorbs radiation and emits it as visible light. So the phosphors in the jelly are absorbing the invisible ultraviolet radiation from the black light and emitting visible light.

Can you find anything else in your home that glows under black light?

One thing that usually glows brightly under black lights is a white shirt. Most laundry detergents contain “bluing agents” that are advertised as making the whites “whiter.” In fact, these agents are phosphors that respond to the UV-A radiation in normal light. The black light emphasizes their presence.

Another example of phosphors can be found on new $20 bills. As part of the government’s program to make currency harder to counterfeit, $20 bills issued since October, 2003, have a “security thread” that glows under ultraviolet light. The security thread is being introduced into $50 and $100 bills as well.

Glowing Hands

Can you think of a way to make your hands glow in the dark?

For this experiment you will need:

• a black light
• petroleum jelly
• latex gloves if you don't want to get your hands messy (caution: some people are allergic to latex gloves!)
• someone to turn on the black light for you.

If you have Latex gloves, put them on your hands. Reach into the jar of petroleum jelly and scoop out enough jelly to cover both hands. Rub the jelly well over both hands, and then ask someone to turn off the lights in the room, and to turn on the black light. Hold your hand under the black light.

What do you see? Can you think of a way you could use this trick when telling ghost stories at night?


1. 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.

2. Liquid nitrogen boils at 77 kelvin (−196 °C, −321 °F).
Around 1% of the sun’s mass is oxygen.

3. Helium is lighter than the air around us so it floats, that's why it is perfect for the balloons you get at parties.

4. Carbon comes in a number of different forms (allotropes), these include diamond, graphite and impure forms such as coal.

5. Although it is still debated, it is largely recognized that the word 'chemistry' comes from an Egyptian word meaning 'earth'.

6. 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.

7. Things invisible to the human eye can often be seen under UV light, which comes in handy for both scientists and detectives.

8. Humans breathe out carbon dioxide (CO2). Using energy from sunlight, plants convert carbon dioxide into food during a process called photosynthesis.

9. 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!

10. Water expands as it drops in temperature, by the time it is frozen it takes up about 9% more space.

11. 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.

12. 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.)


Creating firework colors is a complex endeavor, requiring considerable art and application of physical science. Excluding propellants or special effects, the points of light ejected from fireworks, termed 'stars', generally require an oxygen-producer, fuel, binder (to keep everything where it needs to be), and color producer. There are two main mechanisms of color production in fireworks, incandescence and luminescence.


Incandescence is light produced from heat. Heat causes a substance to become hot and glow, initially emitting infrared, then red, orange, yellow, and white light as it becomes increasingly hotter. When the temperature of a firework is controlled, the glow of components, such as charcoal, can be manipulated to be the desired color (temperature) at the proper time. Metals, such as aluminum, magnesium, and titanium, burn very brightly and are useful for increasing the temperature of the firework.


Luminescence is light produced using energy sources other than heat. Sometimes luminescence is called 'cold light', because it can occur at room temperature and cooler temperatures. To produce luminescence, energy is absorbed by an electron of an atom or molecule, causing it to become excited, but unstable. When the electron returns to a lower energy state the energy is released in the form of a photon (light). The energy of the photon determines its wavelength or color.

Sometimes the salts needed to produce the desired color are unstable. Barium chloride (green) is unstable at room temperatures, so barium must be combined with a more stable compound (e.g., chlorinated rubber). In this case, the chlorine is released in the heat of the burning of the pyrotechnic composition, to then form barium chloride and produce the green color. Copper chloride (blue), on the other hand, is unstable at high temperatures, so the firework cannot get too hot, yet must be bright enough to be seen.


Pure colors require pure ingredients. Even trace amounts of sodium impurities (yellow-orange) are sufficient to overpower or alter other colors. Careful formulation is required so that too much smoke or residue doesn't mask the color. With fireworks, as with other things, cost often relates to quality. Skill of the manufacturer and date the firework was produced greatly affect the final display (or lack thereof).

firework colorants

open this link to view a fireworks video : http://www.youtube.com/watch?v=Aip619LJMDo


Radiation-free nuclear fusion could be possible in the future claim a team of international scientists. This could lead to development of clean and sustainable electricity production.

Despite the myriad of solutions to the energy crisis being developed, nuclear fusion remains the ultimate goal as it has the potential to provide vast quantities of sustainable and clean electricity. But nuclear energy currently comes with a serious environmental and health hazard side effect - radiation. For fusion to gain widespread acceptance, it must be able to produce radiation-free energy but the key to this has so far remained elusive, explains Heinrich Hora at the University of New South Wales in Sydney, Australia.

Conventionally, the fusion process occurs with deuterium and tritium as fuel. The fuel is spherically compressed - meaning compression occurs from all directions - with laser irradiation to 1000 times its solid state density. This ignites the fuel, producing helium atoms, energy and neutrons which cause radiation. Fusion is also possible with hydrogen and boron-11, and this could produce cleaner energy as it does not release neutrons, explains Hora. But this fuel requires much greater amounts of energy to initiate and so has remained unpopular.

Now, a team led by Hora has carried out computational studies to demonstrate that new laser technology capable of producing short but high energy pulses could be used to ignite hydrogen/boron-11 fuel using side-on ignition. The high energy laser pulses can be used to create a plasma block that generates a high density ion beam, which ignites the fuel without it needing to be compressed, explains Hora. Without compression, much lower energy demands than previously thought are needed. 'It was a surprise when we used hydrogen-boron instead of deuterium-tritium. It was not 100 000 times more difficult, it was only ten times,' says Hora.

'This has the potential to be the best route to fusion energy,' says Steve Haan, an expert in nuclear fusion at Lawrence Livermore National Laboratory in California. However, he also points out that it is still only potential at this point, 'there's a fair amount of work to do before this technology is at hand.'

Hora agrees that much more work is needed to fully understand this radical new approach. Its achievement will depend on continued advances in laser optics, target physics and power conversion technology, he concludes.


What Is Chemistry?

Chemistry is the study of matter and energy and the interactions between them. This is also the definition for physics, by the way. Chemistry and physics are specializations of physical science. Chemistry tends to focus on the properties of substances and the interactions between different types of matter, particularly reactions that involve electrons. Physics tends to focus more on the nuclear part of the atom, as well as the subatomic realm. Really, they are two sides of the same coin.

The formal definition of chemistry is probably what you want to use if you're asked this question on a test.

Why Study Chemistry?

Because understanding chemistry helps you to understand the world around you. Cooking is chemistry. Everything you can touch or taste or smell is a chemical. When you study chemistry, you come to understand a bit about how things work. Chemistry isn't secret knowledge, useless to anyone but a scientist. It's the explanation for everyday things, like why laundry detergent works better in hot water or how baking soda works or why not all pain relievers work equally well on a headache. If you know some chemistry, you can make educated choices about everyday products that you use.

What Fields of Study Use Chemistry?

You could use chemistry in most fields, but it's commonly seen in the sciences and in medicine. Chemists, physicists, biologists, and engineers study chemistry. Doctors, nurses, dentists, pharmacists, physical therapists, and veterinarians all take chemistry courses. Science teachers study chemistry. Fire fighters and people who make fireworks learn about chemistry. So do truck drivers, plumbers, artists, hairdressers, chefs... the list is extensive.

What Do Chemists Do?

Whatever they want. Some chemists work in a lab, in a research environment, asking questions and testing hypotheses with experiments. Other chemists may work on a computer developing theories or models or predicting reactions. Some chemists do field work. Others contribute advice on chemistry for projects. Some chemists write. Some chemists teach. The career options are extensive.

Where Can I Get Help With a Chemistry Science Fair Project?

There are several sources for help. A good starting point is the Science Fair Index on this website. Another excellent resource is your local library. Also, do a search for a topic that interests you using a search engine, such as Google.

Where Can I Find Our More About Chemistry?

Start with the Chemistry 101 Topic Index or list of Questions Chemistry Students Ask. Check out your local library. Ask people about the chemistry involved in their jobs.

Where Can I Get Answers to Chemistry Questions?

The Chemistry Forum is a great place for quick answers from scientists, teachers, students, and other people interested in chemistry.