Some of these elements, notably bismuth (atomic number 83), thorium (atomic number 90), and uranium (atomic number 92), have one or more isotopes with half-lives long enough to survive as remnants of the explosive stellar nucleosynthesis that produced the heavy metals before the formation of our Solar System. Elements with atomic numbers 83 through 94 are unstable to the point that radioactive decay of all isotopes can be detected. Isotopes considered stable are those for which no radioactive decay has yet been observed. Of the 94 naturally occurring elements, those with atomic numbers 1 through 82 each have at least one stable isotope (except for technetium, element 43 and promethium, element 61, which have no stable isotopes). New atoms are also naturally produced on Earth as radiogenic daughter isotopes of ongoing radioactive decay processes such as alpha decay, beta decay, spontaneous fission, cluster decay, and other rarer modes of decay.
On Earth, small amounts of new atoms are naturally produced in nucleogenic reactions, or in cosmogenic processes, such as cosmic ray spallation. Almost all other elements found in nature were made by various natural methods of nucleosynthesis. The lightest chemical elements are hydrogen and helium, both created by Big Bang nucleosynthesis during the first 20 minutes of the universe in a ratio of around 3:1 by mass (or 12:1 by number of atoms), along with tiny traces of the next two elements, lithium and beryllium. The discovery and synthesis of further new elements is an ongoing area of scientific study. Save for unstable radioactive elements ( radionuclides) which decay quickly, nearly all of the elements are available industrially in varying amounts. The first 94 occur naturally on Earth, and the remaining 24 are synthetic elements produced in nuclear reactions. The periodic table summarizes various properties of the elements, allowing chemists to derive relationships between them and to make predictions about compounds and potential new ones.īy November 2016, the International Union of Pure and Applied Chemistry had recognized a total of 118 elements. This table organizes the elements by increasing atomic number into rows (" periods") in which the columns (" groups") share recurring ("periodic") physical and chemical properties. Much of the modern understanding of elements developed from the work of Dmitri Mendeleev, a Russian chemist who published the first recognizable periodic table in 1869. Attempts to classify materials such as these resulted in the concepts of classical elements, alchemy, and various similar theories throughout human history. The history of the discovery and use of the elements began with primitive human societies that discovered native minerals like carbon, sulfur, copper and gold (though the concept of a chemical element was not yet understood). Air is primarily a mixture of the elements nitrogen, oxygen, and argon, though it does contain compounds including carbon dioxide and water. Nearly all other naturally occurring elements occur in the Earth as compounds or mixtures.
Only a minority of elements, such as silver and gold, are found uncombined as relatively pure native element minerals. When different elements undergo chemical reactions, atoms are rearranged into new compounds held together by chemical bonds. This is in contrast to chemical compounds and mixtures, which contain atoms with more than one atomic number.Īlmost all of the baryonic matter of the universe is composed of chemical elements (among rare exceptions are neutron stars). For example, oxygen has an atomic number of 8, meaning that each oxygen atom has 8 protons in its nucleus. The basic particle that constitutes a chemical element is the atom, and each chemical element is distinguished by the number of protons in the nuclei of its atoms, known as its atomic number. A chemical element is a chemical substance that cannot be broken down into other substances.
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