Metals

Table of Contents

• Teaching Tip: Learn about Metals
• Science Projects: Experiments with Metals
• Technology: Fireworks & Chemistry
• Fabulous Facts
• Science Links

Teaching Tip: Learn about Metals

An element is a substance made up of all one kind of atom: for example, the element helium (the same stuff that fills balloons) is made up exclusively of helium atoms. Elements are generally classified as metals or nonmetals (although some elements have characteristics of both; these are called metalloids). The majority of elements listed in the periodic table are metals. These elements usually share three main properties:

• Luster: Metals are shiny when cut, scratched, or polished.
• Malleability: Metals are strong but malleable, which means that they can be easily bent or shaped. For centuries, smiths have been able to shape metal objects by heating metal and pounding it with a hammer. If they tried this with nonmetals, the material would shatter! Most metals are also ductile, which means they can be drawn out to make wire.
• Conductivity: Metals are excellent conductors of electricity and heat. Because they are also ductile, they are ideal for electrical wiring. (You can test this using some household items. See our metals science projects article for an activity.)

Metals are categorized in five different groups:

Noble Metals are found as pure metals because they are unreactive and don't combine with other elements to form compounds. Because they are so unreactive, they don't corrode easily. This makes them ideal for jewelry and coins. Noble metals include copper, palladium, silver, platinum, and gold.

Alkali Metals are very reactive. They have low melting points and are soft enough to be cut with a knife. Potassium and sodium are two alkali metals.

Alkaline Earth Metals are found in compounds with many different minerals. They are less reactive than alkali metals, as well as harder, and have higher melting points. This group includes calcium, magnesium, and barium.

Transition Metals are what we usually think of when we think of metals. They are hard and shiny, strong, and easy to shape. They are used for many industrial purposes. This group includes iron, gold, silver, chromium, nickel, and copper, some of which are also noble metals.

Poor Metals are fairly soft, and most are not used very much by themselves. They become very useful when added to other substances, though. Poor metals include aluminum, gallium, tin, thallium, antimony, and bismuth.

Alloys: Strong Combinations

The properties of these different metals can be combined by mixing two or more of them together. The resulting substance is called an alloy. Some of our most useful building materials are actually alloys. Steel, for example, is a mixture of iron and small amounts of carbon and other elements; a combination that is both strong and easy to use. (Add chromium and you get stainless steel. Check your kitchen pots and pans to see how many are made from stainless steel!)

Other alloys like brass (copper and zinc) and bronze (copper and tin) are easy to shape and beautiful to look at. Bronze is also used frequently in ship-building because it is resistant to corrosion from sea water. Titanium is much lighter and less dense than steel, but as strong; and although heavier than aluminum, it's also twice as strong. It's also very resistant to corrosion. All these factors make it an excellent alloy material. Titanium alloys are used in aircraft, ships, and spacecraft, as well as paints, bicycles, and even laptop computers!

Gold, as a pure metal, is so soft that it is always mixed with another metal (usually silver, copper, or zinc) when it's made into jewelry. The purity of gold is measured in karats. The purest you can get in jewelry is 24 karat, which is about 99.7% pure gold. Gold can also be mixed with other metals to change its color; white gold, which is popular for jewelry, is an alloy of gold and platinum or palladium.

• Go to our teaching tip to read about refining metal from ore, metal reactivity, and corrosion.

Science Projects: Experiments with Metals

How Well Does It Conduct?

Metals are excellent conductors of heat and electricity; heat energy and electrons travel very quickly through them. You can experiment with both heat and electricity conduction using items from around your house.

Collect a metal spoon, wooden spoon, and other kitchen implements to compare heat conductivity. Set them in a glass jar of hot, but not boiling, water. Which ones heat up fastest? The ends of the metal utensils should have felt hot first, because they conduct heat better. For a little more excitement, try this activity again using only metal utensils, with a dab of cold butter on top of each utensil. Which one loses its butter first? Why might that be? Look at each utensil's handle thickness and length as well as its top surface area (e.g., a wire whisk has less surface to heat the butter than a ladle does) for clues. Also, keep in mind that some metals conduct heat better than others do.

To test objects for electric conductivity, you'll need a C- or D-size battery, aluminum foil, and a flashlight or other 1.5- or 3-volt bulb. Make a long ribbon wire out of the foil by cutting a piece about 18" x 2". Fold the foil lengthwise in fourths so that you form a ribbon. Hold or tape one end of this wire to the flat end (negative terminal) of the battery and wrap the other end tightly around the "threaded" (screw) sides of the lightbulb. Now you're ready to test various objects around your house to see if they conduct electricity. Do this by pressing the positive terminal of the battery (the end with a bump) to one side of an object, and the metal end of the lightbulb to the other side. If the bulb lights up, a series circuit was formed: electric current can pass unobstructed through the wires from the battery to the lightbulb to the battery again.

What are some variables that could keep the lightbulb from shining even if the object it was touching was a metal? Even though a object may be metal and otherwise a great conductor of electricity, a plastic or paint coating on it could break the circuit connection.

Safety note: Remember never to insert wires or another object into electrical outlets! The electricity generated by the battery for this experiment is in a safe amount, however.

Copper-plating Fun

Try this experiment:   first clean pennies, then watch them oxidize and use them to cover (or plate) an iron nail with copper! Although newer pennies contain only a small amount of copper (2.5%), they still have enough for this project. Fill the bottom of a ceramic or plastic bowl with vinegar, stir in a teaspoon of salt, and then put 10-15 dull pennies in. Let them sit for five minutes, then take them out and set them on a paper towel to dry. (Don't dump out the vinegar and salt yet, though!) The pennies will be much shinier than before; this is because vinegar is an acid that "eats" away the oxide layer on the penny that is making it dull. However, if you don't rinse or dry the clean pennies, after a while you should see a blue layer appear on them. This is a copper oxide compound caused by copper and oxygen reacting with each other;   the vinegar (acetic acid) and salt promote the reaction of oxygen with the copper.

Now stick an ungalvanized iron nail in the vinegar solution. If you look closely, you will see tiny bubbles along the sides of the nail. Let it sit for 30 minutes and then check to see if there is a dark-brown layer of copper on it. How does that happen? The vinegar solution contains copper from the pennies that it cleaned. When the solution reacts with the nail, it makes a chemical exchange that leaves a copper coating on the nail. When you take the nail out of the solution, the copper will be somewhat sticky; you can set it on a paper towel to dry. Your nail might not be entirely coated, but it will have enough copper on it to see.

You might try this experiment again using only pennies made before 1982. These contain 95% copper. Did the nail get a copper coating more quickly or in the same amount of time? Was it a more complete coating?

Technology: Fireworks & Chemistry

If you watched fireworks this Fourth of July, you probably saw an exciting combination of colors and sparks. Did you wonder just how this amazing pyrotechnics display worked? There's a lot of chemistry involved in creating good fireworks!

One of the key ingredients for firecrackers, ground fireworks, and aerial fireworks (ones which explode in the sky) is black powder, invented by the Chinese about 1000 years ago. It's a blend of potassium nitrate (saltpeter), charcoal, and sulfur in a 75:15:10 ratio. Black powder is used to launch aerials and also causes the explosions necessary for special effects like noise or colored light.

In sparklers, black powder is mixed with metal powders and other chemical compounds in a form that will burn slowly, top to bottom. In simple firework rockets, black powder is confined in a tube around a fuse. When lit, the powder creates a force that results in an equal and opposite reaction, pushing the firework off the ground and then causing the compounds inside it to explode in the air. More complex fireworks shells are launched from a mortar, a tube with black powder that causes a lift-off reaction when lit. The firework shell's fuse is then lit as it goes up into the air, and at the right time an explosion inside the shell causes its special effects charges to burst.

The bright, colorful part of the fireworks display is caused by "excited" electrons in the atoms of different metal and salt compounds. These compounds are in little balls called stars, made of a similar compound to what makes a sparkler work. Different metals burn in different colors; for example, if a copper compound is lit, its flame will be a blue-green color. Calcium burns red-colored and potassium burns purple. In fireworks, metals are combined to create different colors.

When the star compounds inside a firework are heated, the excited atoms give off light energy. This light falls into two categories: incandescence and luminescence. Incandescence is light produced from heat:   in fireworks, reactive metals like aluminum and magnesium cause a burst of very bright light when they get hot €”sometimes at temperatures over 5000 ° F! Compounds that are less reactive don't get as hot, resulting in dimmer sparks. Luminescence, on the other hand, is produced from other sources and can occur even at cold temperatures. The electrons in the compound   absorb energy, making them "excited." The electrons can't maintain this high level, though, so they jump back to a lower level, releasing light energy (photons) in the process. Barium chloride is a chemical compound that gives fireworks a luminescent green color, and copper chloride makes a blue color. For either kind of light, it's important to use pure ingredients since traces of other compounds will obscure the color.

Fabulous Facts

Earth Riches. South Africa has the richest known deposit of gold in the world:   20-30% of the gold mined each year comes from there. It is  also one of the world's leading producers in platinum and diamonds.

Really Old Cans. Did you know that "tinned" foods have been around since the early 1800s? The process of canning meats, vegetables, and fruits was discovered during the reign of Napoleon, when both French and British armies needed better nutrition while on the move. Canned goods were packaged in tin-plated iron (for rust-resistance) containers, which were less breakable than glass jars.

Recycling. Steel is the most-recycled material in the United States; most of it comes from scrap vehicles. Aluminum from soda pop cans is another metal that gets recycled a lot. It takes just 4-5% of the energy to recycle aluminum as it does to extract it from its ore, bauxite. Both of these metal alloys - steel and aluminum - can be recycled over and over again! If you're looking for a field trip idea, see if you can get a tour of a local recycling center.

Science Links

Learn how different kinds of fireworks work and how fireworks are made.

Take a virtual tour of Montana's Stillwater palladium mine to discover more about mining and refining this valuable metal.

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