Why is carbon called the element of life?

PROFESSOR DAVE: Hey, it's Professor Dave. Let's talk about carbon.

[THEME SONG] He knows a lot about the science stuff. Professor Dave Explains.

PROFESSOR DAVE: You may have heard that carbon is the element of life. But what does that mean? What determines whether an atom of carbon in the first place? An atom consists of positively charged protons, neutrons, which have no charge, and negatively charged electrons. And element is defined by the number of protons in the nucleus. One proton is hydrogen, two is helium, three, lithium, four, beryllium, five, boron, and six is carbon.

The number of neutrons and electrons can change. But by definition, any atom with six protons is a carbon atom. How do they form? Hydrogen, the simplest and most abundant of all elements, accumulates into clumps due to gravity, which become stars. The tremendous inward pressure triggers nuclear fusion, which is when protons and neutrons smash together and fuse. Many elements, including carbon, and larger ones like iron are made in stars. Much larger ones need the immense energy of a supernova explosion or particle accelerators here on earth.

So what's so special about carbon? Let's look at the electrons. Carbon atoms have six. The first two are in the inner shell, and the other four are the so-called valence electrons in the outer shell. These are the ones available for bonding with other atoms, which happens when two atoms share two electrons. Because elements in this part of the periodic table want to have eight electrons in their outermost shell, carbon has a tendency to make four bonds. These can be single, double, or triple bonds, and with many different elements. In addition, while an atom that's bound to two or three other atoms will adopt a linear or flat shape, a carbon atom that's bound four other atoms will take on a three-dimensional shape because that's how the electron clouds on the four atoms can be as far away from each other as possible.

So it's the ability of carbon to bond in a wide variety of shapes with so many elements, including itself, that makes it so special. Also, carbon-carbon bonds are strong enough to be stable, but not so strong that they can't break and rearrange, which makes them excellent building blocks. When by itself, carbon has many allotropes, or ways an element can be arranged-- there's the graphite in your pencil, which consists of slippery sheets of carbon that rub off easily; there's diamond, the hardest substance known. And we can even make interesting structures like nanotubes and fullerenes.

That's just carbon by itself. When combined with hydrogen, oxygen, nitrogen, and a few other elements, it makes all the diverse structures in your body, including carbohydrates, proteins, and DNA. We can take nature a step further and synthesize novel materials with an array of purposes. Putting carbons in the empty spots of an iron lattice makes it stronger. We call this steel, which is used in most of the large structures we know today. Teflon, carbon-fluorine polymer, is a nonstick substance that's highly resistant to chemical degradation. And carbon-based synthetic drugs like inhibitors, that can silence a faulty enzyme, hold the prospect of curing so many diseases.

That's a lot of reasons to love carbon. It really is the element of life.