Production of Conduction

Finally, let's talk about a metal's amazing ability to conduct electricity. Do you know what metal the wires in your house are made of? Here's a hint - they're probably brown. That's right - copper! Copper isn't actually the best metallic conductor of electricity. Silver is, but it's too expensive to use for wiring.

You can easily compare the conducting ability of metal to that of some other common materials using a flashlight. The best kind for this experiment is a cylindrical flashlight with a removable cap on one end. When you take the cap off, you should see the end of one of the batteries. First, make sure that the flashlight turns on! Then remove the cap, and place a small piece of aluminum foil on top of the battery you can see. Replace the cap, and turn the flashlight on. Does it still work? Open it up again, take the foil out, and put a small piece of paper in. Close it up again. What happens now? Try other materials you have around the house, like a small coin, plastic wrap, waxed paper, or any other thin solid that fits.

What you found was that the flashlight would only light up when you put a piece of metal in. Other materials didn't work. That's because those other things are insulators, which don't let electricity flow.

So how are metals different from insulators? The answer has to do with their electrons (not so surprising, considering that we're talking about electrical conduction!). In insulators, the electrons are stuck between the atoms of the material, and can't move around easily. But in metals, the electrons are free to move around, traveling from the area around one atomic nucleus to another. They're said to be delocalized, and the metal nuclei are sometimes described as being in a "sea of electrons". Normally, they just mill around in an unorganized way. But when the metal is hooked up to a battery or other source of electrical power, suddenly the electrons all start moving in one direction, creating an electrical current. Here's an animation that illustrates this.

Liquid Metals

You may know that metals will melt if you get them hot enough, and may have seen pictures of molten steel being formed into useful objects. Do you know how how steel is? It's about 2500^oF (1370^oC)! Yikes, that's hot! But steel is nowhere near being the highest-melting metal. That distinction goes to tungsten (6200^oF or 3400^oC).

OK, so what's the lowest-melting metal? You may know the answer to this. It's a liquid, silvery metal that is sometimes used in thermometers - mercury! It's not so common to find mercury thermometers today. This metal is very poisonous, so people avoid using it whenever possible. Most thermometers now use a kind of alcohol (usually a red or green liquid) instead. But this is beside the point - what is mercury's melting point? Brrr... it's a chilly -40^oF, which oddly enough, happens to also be -40^oC. But there's another metal, called gallium, that would liquefy on a warm enough day. Its melting point is 86^oF (30^oC). The photo above shows a small sample of gallium actually melting in Dr. B's hand!

Steel Away!

One of the most common metals used in today's world is steel. Steel is mostly iron, but it also contains other elements. As we've already seen, this kind of metal mixture is called an alloy. Most steel contains carbon in addition to iron. Stainless steel also has some chromium, and it doesn't rust. Other types include elements such as molybdenum, vanadium, tungsten, nickel, silicon, manganese, or boron. Different types of steel are used for different purposes. Some are good at high temperatures; others are hard and good at cutting.

The next time you're in a hardware or home-improvement store, take a look at the tools. How many different kinds of steel can you find?

All About Alloys

There are some familiar metals that are actually mixtures of several different types of metals - they are called alloys (AL-oise). Here are a few you've probably heard of (and some that are likely new to you):

• Steel: mixture of iron and one or more other metals (there will be a separate post about steel later)
• Brass (copper and zinc): a shiny yellow metal that looks a little like gold
• Bronze (copper and tin): a dark gold to brown metal that gets darker in color as it ages
• Pewter (copper, tin, and lead): a dark gray metal used for bowls, flatware, jewelry and other decorative items
• Solder (lead and usually tin): an alloy that melts at a relatively low temperature; used to make electrical circuits
• Nitinol (nickel and titanium): this alloy remembers its original shape; used to make eyeglass frames
• Electrum (gold and silver): also known as white gold; used in jewelry
• Alnico (aluminum, nickel, and copper): used to make magnets
• Amalgam (silver, tin, copper, zinc, and mercury): a soft alloy that has been used to fill dental cavities
• Nichrome (nickel and chromium): an alloy that glows orange-red and gives off heat when an electrical current is passed through it; used in toasters and electric burners

Take a look around your house and see how many examples of alloys you can find!

Leaf It!

Have you ever heard of gilding? This is the process of applying a thin gold coating to an object, to make it look like it is made of pure gold. The gold comes in very thin sheets called gold leaf; they are so thin that you'd have to stack about a million of them to make a pile one inch high! Most materials can't be made so thin. Imagine trying to pound a solid piece of wood or plastic that thin; it would break way before it got to 1/1,000,000 of an inch! The ability of metals, and gold in particular, to be made into extremely thin sheets is referred to as malleability (MAL-ee-ah-bill-i-tee).

With an adult's help, you can gild something using a gold leafing kit you can find at a crafts store for about $10. Maybe a picture frame or a piece of jewelry? What are your ideas?

Properties of Metals

If you look around you, you'll see metals used to make a lot of different things. Metals can do lots of interesting things that other materials can't. Some of these properties are:

• Malleability (MAL-ee-ah-bill-i-tee) and ductility (duck-TILL-i-tee): the ability of metals to be pounded into very thin sheets (malleability) or stretched out into wires (ductility) without breaking.
• Luster: metals tend to be shiny
• Electrical conductivity: the ability of metals to let electrical currents pass through
• Thermal conductivity: the ability of metals to transport heat
• Chemical reactivity: some metals react easily; others hardly react at all

You'll do some activities and experiments that illustrate these properties as this month goes on.

Explosive Metals

So, now you know that elements like sodium and potassium are metals. But, you might be thinking, isn't table salt also known as sodium chloride? Is salt a metal? And don't bananas and oranges contain a lot of the nutrient potassium? Do these fruits contain pieces of metal?

Well, no. Chemical elements come in different forms, depending on whether they're pure substances or in compounds, with two or more elements combined. Pure sodium and pure potassium are metals. They're gray and shiny, like most metals. They can be cut with a kitchen knife, which is kind of weird. But they are definitely metals. However, when sodium combines with chlorine (another element), it makes sodium chloride, a compound with properties very different from those of the original elements.

One more thing about the alkali metals, which include sodium and potassium, but also lithium, rubidium, cesium, and francium - they explode and burn when they contact water! This is much too dangerous for you to try on your own, but here's a link to a video in which you can see the Mythbusters playing with sodium and potassium.

Test Your Metal!

Quick - name fifteen metals!!

What did you come up with? You probably started with iron, gold, silver, aluminum, tin, lead, and/or copper; they're pretty easy. After thinking a little harder, you might come up with magnesium, titanium, chromium, nickel, zinc, platinum, and vanadium. That's still not fifteen! There are actually over 50 chemical elements that are metals. You may know some of them, even if you didn't come up with their names right away - cobalt, mercury palladium, cadmium, tungsten, iridium. Some metallic elements have familiar names - sodium, potassium, calcium, barium - but we rarely see them in metallic form. And there are some metals that are kind of rare and/or exotic, and you may have never heard of them - ruthenium, rhenium, yttrium, hafnium, bohrium, meitnerium. This month, we'll learn about some of the common and not so common metals in your world!

PS: Did you say "steel" for one of your metals? Steel is a combination of iron (mostly) and other elements, so it's not a pure metal by itself. We'll talk more about steel later.

Make a Magnet!

We tend to think that some things are magnetic, and that some just aren't. But there are some non-magnetic materials that can be magnetized - they can be turned into magnets, and sometimes very simply. Here's an example:


What you'll need:
Screwdriver
Small magnet (not the flexible kind)
Metal paper clips


Hold the tip of the screwdriver near a small pile of paper clips. Does it pick them up? Probably not, because a normal screwdriver isn't a magnet (if your screwdriver is already magnetic, find another one for this experiment).


Hold the screwdriver tightly by the handle in one hand. With the other hand, rub the magnet along the metal part (blade) of the screwdriver, starting near the handle and moving along the blade to the tip. Keep rubbing for about one minute. Now try picking up some paper clips. What happens?


Wow - the screwdriver is now a magnet! But it's made out of the same metal as at the beginning of the experiment. So, some materials can be turned into magnets! How did this happen? The actual explanation is pretty complicated, but here's a simple way to think of this. You probably know that the ends of a magnet are different - it has both a "north" and a "south" pole. The atoms in the screwdriver blade act like little tiny magnets, with itsy-bitsy north and south poles. If the blade is not magnetized, the magnetic atoms are very disorganized, going every which way at once, pulling in every direction. When you rub the metal with a magnet, you help to line up these atoms so that they all point in the same direction. Now they all work together, and the screwdriver acts like a magnet.


Try magnetizing things made out of other materials, such as plastic, wood, or other kinds of metal. You'll find that only certain kinds of metals can be easily magnetized in this way - these metals are called ferromagnetic. This word comes from the Latin name for iron, "ferrum", because the most common magnetizable metal is iron (and steel). However, a few other metals, such as nickel and cobalt, are also referred to as ferromagnetic, even though they're not iron.