Isotopes of Carbon

Carbon is one of the most important elements on Earth and forms the chemical basis of life. It is the fifteenth most abundant element in the Earth's crust and the fourth most abundant element in the entire universe, in terms of mass.

What is an Isotope?
The identity of a distinct chemical element is established by its unique atomic number. Atomic number is the number of protons in an atomic nucleus. Another property is the atomic mass of the element, which is the sum of protons and neutrons in the nucleus or the mass of the atomic nucleus. The nuclei of same chemical element may have the same atomic number but different atomic mass numbers. Such nuclei are called the isotopes of the element. Since, the chemical properties depend on the atomic number, these isotopes are chemically similar, but differ in certain physical properties.

How Many Isotopes of Carbon Exist?
Just how many carbon isotopes are there? Carbon has as many as 15 isotopes! They all have an atomic number of 6, but differ in their atomic masses. Though they all have the same number of protons (6), each one differs in the number of neutrons, in the nucleus. Most of them are radioactive. Radioactivity indicates that these nuclei are unstable and decay by emitting ionizing radiation. Here is a list of all the isotopes, along with some of their most important properties.

Carbon Isotope	Neutron Number	Atomic Weight (in amu)	Half Life
C8	2	8.037675	2.0 x 10-21 sec
C9	3	9.0310367	126.5 millisec
C10	4	10.0168532	19.290 sec
C11	5	11.0114336	20.334 min
C12	6	12	Stable (Non-Radioactive)
C13	7	13.0033548378	Stable (Non-Radioactive)
C14	8	14.003241989	5.70 x 103 years
C15	9	15.0105993	2.449 sec
C16	10	16.014701	0.747 sec
C17	11	17.022586	193 msec
C18	12	18.02676	92 msec
C19	13	19.03481	46.2 msec
C20	14	20.04032	16 msec
C21	15	21.04934	Less than 30 ns
C22	16	22.05720	6.2 msec

Which are the most Stable Isotopes?
As you can see in the table above, almost all but three of the carbon isotopes are unstable and exist for very short periods of time, before they decay. Out of the 15, 13 are radioactive isotopes. The three most stable are C¹², C¹³ and C¹⁴. These are also the naturally occurring isotopes, while others are created through artificial transmutation of elements. Of these three, C¹⁴ is radioactive, while the other two aren't. C¹² is the most abundant on Earth, constituting about 98.93% of the atoms in one mole of carbon, C¹³ is about 1.07% and C¹⁴ is the rarest (1 part in trillion).

What are They Used For?
Uses of carbon are many. C¹² being the most abundant of the three carbon isotopes and this element being the backbone of life on Earth, the uses of carbon are endless. All metabolic processes including the life sustaining processes of respiration and photosynthesis, are made possible by carbon based compounds. The fossil fuels are created from dead carbon based organic matter. All our energy needs are satisfied by carbon based crude oil and natural gas deposits.

C¹³ has applications in NMR (Nuclear Magnetic Resonance), as it has a nuclear spin, which can respond to a radio frequency signal (as opposed to C¹² which hasn't). Protein structure determination using NMR is made possible with the labeling of proteins with C¹³ atoms. In Earth science, C¹³ is used to determine identity of water sources by studying its ratio with respect to other carbon isotopes.

C¹⁴ is the radioactive isotope of carbon that is primarily used in radiocarbon dating technique. Using this technique, archaeologists can determine the age of carbon containing materials which are up to 60,00 years old. A knowledge of the half life of C¹⁴, along with the current ratio of C¹² to C¹⁴, helps in determining the age of archeological objects.

Carbon is the most versatile of all elements when you analyze its wide range of applications in nature. Being the fourth most abundant element in the universe, most galactic systems and most stars with solar systems are bound to have a carbon based life, similar to life based on Earth!