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In which part of a pencil would you find metallic bond?
Question Date: 2005-04-09
Answer 1:

Great question! It turns out, that something as simple as a pencil has many interesting types of bonds within it, including metallic bonds. In a pencil, there are 4 major components: the wood, the"lead", the eraser, and the metal band that holds the eraser, which is most likely made up of aluminum. Before the 1800s lead metal was used in pencils, but it has now been replaced with a non-toxic material called graphite.

The wood, graphite, and the eraser all contain "covalently bonded" molecules. A covalent bond is a bond in which electrons are shared between 2 or more atoms making up the molecule. The way these covalently bonded molecules are arranged gives the different materials that make up the wood, the graphite and the eraser different properties. For example, think of some bricks. If you were to toss bricks into a random, messy pile, this would be similar to the way that the molecules are arranged in the wood. The technical name for this is "amorphous". If you were to stack them nicely like in a brick wall, they would be arranged like they are in the graphite, which is technically called a "covalent crystal".

If the bricks were lined up like railroad tracks, they would be like the molecules in the eraser, which is technically called a "polymer". All of these materials, however, are covalently bonded, not metallic. A metallic bond is a continuous, long reaching bond between thousands of atoms in 3 dimensions, like a large 3-D cube made of bricks.

Because of this type of bonding, the electrons in a metallic bond can move all around in the piece of metal, which is what gives metal the ability to conduct electricity. It also makes metal very strong!

So nowadays, since the replacement of lead with graphite in 1820s, the only place metallic bonding occurs in a pencil is in the shiny aluminum piece that hold on your eraser. One interesting experiment--try touching the aluminum part of a pencil and compare that to touching the wood. Why does the aluminum part feel colder? Metal also turns out to be a good conductor of heat, so it takes the heat from your finger and makes your finger feel cold. This is also because of the way the atoms are bound together-in 3 dimensions.

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