From thermometers to utensils, from vehicles to ornaments, elements are everywhere. So, let us understand what this so important “elements” are.An element is a substance that is made entirely from one type of atom. For example, graphite. The tip of the pencil contains graphite, and graphite is made up of carbon atoms. Under the microscope the carbon atoms look like this.
All the elements have atoms with certain number of protons and neutrons. These elements are either seen in nature or are manmade (which are made in laboratory with the help of certain nuclear reactions). These elements have been arranged in the periodic table as per the number of protons present in them (which is also called atomic number). Out of these elements some are called metals, some are called non metals and some are called metalloids.
Just like our birth these elements also are born in some parts of the universe at some time during some processes. Let’s know about some of those processes.
Our sun is a star and like most stars the major source of energy produced by them is by the nuclear fusion (i.e. merging of lighter elements to give a heavier element) where the hydrogen is converted to helium. Research say that 73 % of all materials present in the universe is hydrogen and 25 % is helium and the rest 2 % is all other elements. Hydrogen and helium mostly came to the picture during big bang. As per this big bang theory, at first there were no matter but only energy. Slowly, the electrons, protons and other particles formed. As the universe slowly cooled down as it expanded, elements like hydrogen formed and then helium formed via a process called radiative capture where neutrons and protons merge with the nucleus of an atom to make another atom. Then heavier elements like lithium, beryllium and boron formed slowly. Two helium nuclei come together to make beryllium. Adding another helium gives carbon using the triple alpha process and yet another gives oxygen. These nuclear fusions happen inside the stars. After this these types merging of lighter elements to make heavier elements till iron in the periodic table started happening.
Elements till zinc could be made by adding helium to other lighter elements. But elements heavier than iron are less stable than iron. We can understand this using the following graph. Iron is the most stable element of all because it has higher binding energy of all elements. This is the reason why most stars have iron core. Then, what is binding energy? Binding energy is the energy required to separate an atomic nucleus completely into its constituent protons and neutrons. So, higher binding energy would mean that it is difficult to separate or very high amount of energy is required to separate iron nucleus into protons and neutrons completely. When elements lighter than iron combine to form a heavier element (but lighter than iron), they give out energy. When elements heavier than iron disintegrate to give lighter elements (but heavier than iron), they give out energy. It can be simply thought of as the energy when we subtract the corresponding binding energy of the elements in the graph. If we get positive result then the conversion will give off energy and if we get negative result then the conversion will require energy to happen.
So neutron capture is used to build such elements. Neutron capture is again divided into two parts- slow neutron capture and rapid neutron capture. Slow neutron capture (s-process) occurs in stars with 0.6 to 10 solar mass. Neutron is captured by iron to produce cobalt then nickel and so on. The rapid neutron capture (r-process) occurs in colliding neutron star or supernovae (explosion of stars after death).
Lithium, beryllium and boron are also produced when cosmic rays disintegrate the larger elements like carbon, nitrogen and oxygen respectively. Very heavy elements after Bismuth occur by p-process. But this process is very less understood. Elements like Tc, Po, At, Rn, Fr, Ra, Pm, Ac, Pa, Np, Pu are produced using decay of uranium and thorium. Others origin have not been found in nature and hence are called synthetic or man-made elements. The main reason of they being not found elsewhere is there very low stability (i.e. they can disintegrate to lighter element within seconds). But there is every possibility that we can find these elements as we become technically more advanced.
Till then be curious and keep learning. Who knows you might be the next one to discover the origin of elements.
Barnali Das, IISER, Kolkata
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