Carbon

Purpose of carbon

Due to carbon's properties, it is a building block of life. All living things are made up of carbon. The whole field of organic chemistry is dedicated to carbon, that's one important element!

Now that I have sufficiently hyped up carbon, let's look at its properties, shall we?

Physical properties of carbon

Carbon has a melting point of 3,652 °C and a boiling point of 4,827 °C, so it is almost always present as a solid. It is soft and either dull grey or black. Some of its physical properties are dependent on the allotrope.

Two of the most common carbon allotropes are graphite and diamond.

Graphite is soft, light, and a good conductor of heat and electricity. It has a density of 2.26 g/cm³. Diamond, on the other hand, is hard, strong, and a poor conductor of electricity (but is a good conductor of heat). Its density is 3.51 g/cm³.

Not only are they different physically, but chemically as well. Graphite can react violently with strong oxidizing agents like fluorine, and graphite dust and air are explosive when ignited. Diamond doesn't react at all at room temperature, but can catch fire around 690 °C if put in an environment of pure oxygen.

These differences are dependent on how the carbon atoms are arranged. Below is a comparison between the two structures:

Fig. 1: Comparison of the structures of diamond and graphite. Wikimedia commons.

Diamond's atoms are arranged in a hexagonal lattice and have a crystalline structure. The atoms in graphite are also arranged hexagonally but are in flat sheets, which is why it's much weaker.

The different allotropes make carbon a jack-of-all-trades. While these two are the most common, there are many more. Here is a table with some more carbon allotropes:

Several of these allotropes (like diamine), only exist in certain conditions like high-pressure environments.

Atomic structure of carbon

To help us understand the chemical properties of carbon, we should first look at its Atomic Structure.

Carbon's entry on the periodic table tells us the basics about its structure:

Fig. 2: Carbon's entry on the periodic table

Looking at the atomic number, we know that carbon has 6 protons. Carbon has an atomic weight of 12.01 amu (atomic mass units), and its most common isotope has 6 neutrons.

For example, carbon-14 is an isotope of carbon that has 8 neutrons. It is also the isotope used in carbon dating.

Here is carbon's atomic structure:

Fig. 3: Neutral carbon's atomic structure. Wikimedia commons.

Carbon has two core electrons and four valence electrons.

Carbon's four valence electrons are a main reason why it is so important, which we will get to in the next section.

Chemical properties of carbon

Since carbon has four valence electrons, it can form 4 covalent bonds.

Carbon is incredibly versatile. It can perform 4 types of reactions:

1. Combustion: Carbon combines with oxygen to produce heat energy

$$CH_4+2O_2 \rightarrow CO_2 + 2H_2O$$

2. Oxidation: Oxygen is added to carbon

$$CH_3CH_2OH + O \rightarrow CH_3CHO + H_2O$$

3. Addition: An element/compound is added to an element/compound

$$HCCH + HI \rightarrow H_2CCHI$$

4. Substitution: An element/compound substituted in for another element/compound

$$CH_3Cl + OH \rightarrow Cl^- + CH_3OH$$

We currently know approx. 1 million hydrocarbon compounds and that number increases every year! While carbon can form a number of inorganic (non-C-H) molecules, there are a lot fewer of those. Carbon, in total, forms more compounds than all the other elements, combined. That's a lot of compounds!

Uses of carbon

Carbon has a a lot of uses. Here is just a small chunk of its uses:

• Used in fossil fuels (hydrocarbons).
• Used in pencils (graphite).
• Used in jewelry (diamond).
• Breathed in by plants and converted to oxygen (photosynthesis) (CO₂).
• Used in high tensile strength materials (fullerene/buckyball).
• 12% of the human body (elemental carbon).

There are a lot more uses, but these give you a good look into how widespread carbon is. They don't call it a building block of life for nothing!