This method works on once-living organisms, including objects made of wood or other plant material. Carbon-14 has a half-life of 5,730 years, meaning that after that time, half of the carbon-14 in a sample decays away, according to the University of Arizona.īecause organisms stop taking in carbon-14 after death, scientists can use carbon-14's half-life as a sort of clock to measure how long it has been since the organism died. Animals incorporate carbon-14 into their bodies by eating plants or other plant-eating animals. Plants take it up in respiration, in which they convert sugars made during photosynthesis back into energy that they use to grow and maintain other processes, according to the Iowa State University Center for Nondestructive Evaluation. Carbon-14 is naturally occurring in the atmosphere. Coal is also a key component in steel production, while graphite, another form of carbon, is a common industrial lubricant.Ĭarbon-14 is a radioactive isotope of carbon used by archaeologists to date objects and remains.

Carbon as coal is still a major source of fuel worldwide, providing about 37% of the world's electricity, according to the World Coal Association. The element was known to prehistoric humans in the form of charcoal. (Image credit: Nandalal Sarkar via Shutterstock)Ĭarbon's discovery is lost to history. This illustrations shows the atomic structure of Carbon-12, Carbon-13 and Carbon-14. Carbon's incredible ability to bond with many other elements is a major reason that it is crucial to almost all life.Ĭarbon isotopes come in three forms. And it uses them: Nearly 10 million carbon compounds have been discovered, and scientists estimate that carbon is the keystone for 95% of known compounds, according to the website Chemistry Explained. (It can also bond stably to fewer atoms by forming double and triple bonds.) Carbon has four empty spaces in its outer shell, enabling it to bond to four other atoms.

When atoms bond, they share electrons in their outermost shell. Carbon has two electron shells, with the first holding two electrons and the second holding four out of a possible eight spaces. Chemists conceive of these distances as shells, and define the properties of atoms by what is in each shell, according to the University of California, Davis. Atoms are arranged as a nucleus surrounded by an electron cloud, with electrons zinging around at different distances from the nucleus. It can also bond with up to four other atoms because of its electron arrangement. It can link to itself, forming long, resilient chains called polymers. The extent of the deflection depends on the mass-to-charge ratio of the ion.Carbon is a pattern maker. When an electric field is applied, the ions are accelerated into a separate chamber where they are deflected from their initial trajectory by a magnetic field, like the electrons in Thomson’s experiment. First, electrons are removed from or added to atoms or molecules, thus producing charged particles called ions.

The technique is conceptually similar to the one Thomson used to determine the mass-to-charge ratio of the electron. Scientists can measure relative atomic masses very accurately, however, using an instrument called a mass spectrometer. Although the difference in mass is small, it is extremely important because it is the source of the huge amounts of energy released in nuclear reactions.īecause atoms are much too small to measure individually and do not have charges, there is no convenient way to accurately measure absolute atomic masses. For example, the ratio of the masses of 1H (hydrogen) and 2H (deuterium) is actually 0.500384, rather than 0.49979 as predicted from the numbers of neutrons and protons present. Once the masses of atoms were determined, the amu could be assigned an actual value:ġ amu = 1.66054 x 10 -24 grams conversely: 1 gram = 6.02214 x 10 23 amuĪlthough the masses of the electron, the proton, and the neutron are known to a high degree of precision ( Table 2.3.1), the mass of any given atom is not simply the sum of the masses of its electrons, protons, and neutrons. Thus, the mass of the hydrogen atom ( 1H) is 1.0080 amu, and the mass of an oxygen atom ( 16O) is 15.995 amu. The atomic mass unit ( amu) was not standardized against hydrogen, but rather, against the 12C isotope of carbon ( amu = 12). As we saw earlier, it is convenient to use a reference unit when dealing with such small numbers: the atomic mass unit. We now know that a hydrogen atom has a mass of 1.6735 x 10 -24 grams, and that the oxygen atom has a mass of 2.6561 X 10 -23 grams. Thus, oxygen was assigned an atomic mass of 16. Hydrogen, the lightest element, was assigned a relative mass of '1', and the other elements were assigned 'atomic masses' relative to this value for hydrogen.

Atomic mass of carbon