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A chemical element, often simply called an element, is a type of atom which has a specific number of protons in its atomic nucleus (i.e., a specific atomic number, or Z). [ 1 ] The definitive visualisation of all 118 elements is the periodic table of the elements , whose history along the principles of the periodic law was one of the founding ...
Of the 94 natural elements, eighty have a stable isotope and one more has an almost-stable isotope (with a half-life of 2.01×10 19 years, over a billion times the age of the universe). [15] [b] Two more, thorium and uranium, have isotopes undergoing radioactive decay with a half-life comparable to the age of the Earth.
In physics, natural abundance (NA) refers to the abundance of isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average, weighted by mole-fraction abundance figures) of these isotopes is the atomic weight listed for the element in the periodic table. The abundance of an isotope varies from ...
A chemical element is a chemical substance whose atoms all have the same number of protons.The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8, meaning each oxygen atom has 8 protons in its nucleus.
92 astatine-215: 100 astatine-216m: 100 protactinium-218: 113 lead-206m1: ... Lists of isotopes, by element; Notes External links. Radioactive isotope table ...
The abundance of the chemical elements is a measure of the occurrences of the chemical elements relative to all other elements in a given environment. Abundance is measured in one of three ways: by mass fraction (in commercial contexts often called weight fraction), by mole fraction (fraction of atoms by numerical count, or sometimes fraction of molecules in gases), or by volume fraction.
Natural isotopes are either stable isotopes or radioactive isotopes that have a sufficiently long half-life to allow them to exist in substantial concentrations in the Earth (such as bismuth-209, with a half-life of 1.9 × 10 19 years, potassium-40 with a half-life of 1.251(3) × 10 9 years), daughter products of those isotopes (such as 234 Th, with a half-life of 24 days) or cosmogenic ...
A large fraction of the chemical elements that occur naturally on the Earth's surface are essential to the structure and metabolism of living things. Four of these elements (hydrogen, carbon, nitrogen, and oxygen) are essential to every living thing and collectively make up 99% of the mass of protoplasm. [1]