Origin of the elements
The synthesis of elements needs nuclear reactions of which the most significant type is the fusion of two light nuclei to create one of higher charge and mass. The attractive strong interaction, that holds neutrons and protons together, and operates only over extremely short distances (approximately 10-15 m) and is opposed at longer range through the electrostatic repulsion among positively charged protons. To get two nuclei close sufficient together for fusion requires extremely high energies that are generally found only at high temperatures (above 107 K) in the interior of stars. Under such type of circumstances the chemical properties of elements are inappropriate, as no compounds can present, atoms being in highly ionized states stripped of their electrons.
It is an idea that the Universe began approximately 15 billion years ago in a state of extraordinarily extreme temperature and pressure termed as the big bang. It quickly cooled, and exotic elementary particles originally exists formed protons, electrons and neutrons. Some neutrons and protons combined to create nuclei of deuterium (2H, the heavy isotope of hydrogen;), that then fused to create 4He nuclei. Due to the fast falling temperature nuclear reactions ceased after about 3 min, and only extremely tiny amounts of elements heavier than helium were created. Calculations that are based on the assumed circumstances agree very well along with the observed abundance of hydrogen and helium in the Universe. The dominance of these elements creates one of the strongest pieces of proof for the big bang model.
Like hydrogen and helium cooled, local gas concentrations created and contracted within gravitational forces. Release of the gravitational potential energy heated the center of each concentration to the temperature (approximately 107 K) in which nuclear fusion reactions restarted. The energy output of all stars, with our Sun, comes from such type of reactions. Fusion of hydrogen nuclei creates helium, and forms the energy source for stars during most of their lifetime. While hydrogen is used up in the center of a star, additional gravitational contraction increases the temperature to about 108 K and 4He nuclei themselves begin to fuse. The major products of this stage are 12C and 16O, the mainly abundant nuclei in the
Universe after H and He. Exhaustion of He provides higher temperatures and additional fusion reactions, making elements up to approximately iron. 56Fe has the highest binding energy of all nuclei, fusion reactions producing heavier nuclei being endothermic. Elements such as Co and Ni just across Fe are produced in equilibrium at the extremely high temperatures (above 109 K) at the center of a star with in the final stages of its life, although across this point successive elements are formed through a process of neutron capture. Neutrons are produced like side results of some of the fusion reactions. They might be captured by nuclei, followed through a radioactive β decay process, that leads to an element of higher atomic number. Successive capture and decay procedures are thought to have produced all the heavy elements, possibly including a few transuranium elements which have consequently decayed.
When no additional exothermic nuclear reactions are feasible in the center of a star, it collapses within gravitational attraction, that releases sufficient energy to cause a gigantic explosion termed as a supernova, that throws most of the material 'cooked' through nuclear reactions into space. Studies of supernovae in close galaxies depict atomic spectral lines confirming the existence of these elements.
Calculations that are based on these ideas can account for the abundance of elements, and of their dissimilar isotopes, observed in the Universe. The nuclei prepared in greatest numbers are the most stable ones, usually having even numbers of neutrons and protons. Across 12C and 16O the most abundant are 20Ne, 24Mg, 28Si, 32S and 56Fe. Because of this reason (that has nothing to do with chemistry) elements within odd-numbered groups in the periodic table be likely to be less general than in even-numbered ones, a pattern that is visible in the composition of the whole Earth.