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Protactinium is a chemical element; it has symbol Pa and atomic number 91. It is a dense, radioactive , silvery-gray actinide metal which readily reacts with oxygen , water vapor, and inorganic acids .
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 ...
This is a list of chemical elements and their atomic properties, ... a purely formal definition as number of electrons in the outermost shell has been ... 91.224(2) 1 ...
Each distinct atomic number therefore corresponds to a class of atom: these classes are called the chemical elements. [5] The chemical elements are what the periodic table classifies and organizes. Hydrogen is the element with atomic number 1; helium, atomic number 2; lithium, atomic number 3; and so on.
where Z is the atomic number, and α is the fine-structure constant, a measure of the strength of electromagnetic interactions. [96] Under this approximation, any element with an atomic number of greater than 137 would require 1s electrons to be traveling faster than c, the speed of light. Hence, the non-relativistic Bohr model is inaccurate ...
Yttrium is a chemical element; it has symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". [8] Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals and is never found in nature as a free ...
91 Protactinium: List: 211 Pa 212 Pa 213 Pa 214 Pa 215 ... Wikipedia: WikiProject Elements/Isotope tables/Element 91-100. Add languages ...
The figure buildup of actinides is a table of nuclides with the number of neutrons on the horizontal axis (isotopes) and the number of protons on the vertical axis (elements). The red dot divides the nuclides in two groups, so the figure is more compact. Each nuclide is represented by a square with the mass number of the element and its half ...