8th Grade Chemistry Ms. Mudd Carbon Chemistry 8th Grade Chemistry Ms. Mudd

Key concepts Key Terms How is carbon able to form such a huge variety of compounds? What are four forms of pure carbon? Diamond Graphite Fullerene Nanotube Properties of Carbon

Carbon Atoms and Bonding The atomic number of carbon is 6, which means the nucleus of a carbon atom contains 6 protons. Surrounding the nucleus is 6 electrons. Four are valence electrons-electrons available for bonding. A bond is a chemical force that holds two atoms together. Two atoms gain, lose, or share valence electrons in a way to make the atoms more stable. The transfer or sharing of valence electrons creates chemical bonds. Atoms of most elements form chemical bonds.

Carbon Atoms and Bonding Carbon is unique. Few elements have the ability of carbon to bond with both itself and other elements in so many different ways. With four valence electrons, each carbon atom is able to form four bonds. It is possible to form molecules made of thousands of carbon atoms. By comparison, hydrogen, oxygen, and nitrogen can only form one, two, or three bonds. Carbon atoms can form straight chains, branched chains, and rings. Sometimes two or more rings can join together.

Forms of Pure Carbon Because of the ways that carbon forms bonds, the pure element can exist in many forms. Diamond, graphite, fullerenes, and nanotubes are the four forms of the element carbon.

Diamond The hardest mineral, diamond, forms deep within Earth. At very high temperatures and pressures, carbon atoms form crystals. Each carbon atom is bonded strongly to form other carbon atoms. The result is a solid that is extremely hard and nonreactive. The melting point of diamond is more than 3,500 C˚- as hot as some stars. Diamonds are prized for their brilliance and clarity when cut as gems. Chemists are able to make fake diamonds, but they are not considered beautiful enough to use as gems. Diamonds work well in cutting tools, such as drills.

Fullerenes In 1985 scientists made a new form of carbon. It consists of carbon atoms arranged in the shape of a hollow sphere. This form of carbon was named fullerene, for the architect Buckminster Fuller, who designed dome-shaped buildings called geodesic domes. One type of fullerenes has been nicknamed “buckyballs.”

Graphite Very time you write with a pencil, you leave a layer of carbon on the paper. The “lead” in a lead pencil is actually mostly graphite. In graphite, each carbon atom is bonded tightly to three other carbon atoms in flat layers. The bonds between the layers are very weak, so the layers slide past one another easily. If you run your finger over the pencil marks, you can feel how slippery graphite is. This also makes it a great lubricant in machines. Graphite reduces friction between the moving parts.

Nanotubes In 1991, another form of carbon was made-the nanotube. In a nanotube, carbon atoms arranged in the shape of a long hollow cylinder, or tube. You can think of a nanotube as a sheet of graphite rolled into a tube. Only a few nanometers wide in diameter, nanotubes are tiny, light, flexible, and extremely strong. Nanotubes are also good conductors of electricity and heat. Scientists are looking for ways to use the unique properties of fullerenes and nanotubes. Possibly delivery of medicines molecules into cells. Conductors in electronic devices and super strong cables.