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Potassium: Elements
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Potassium (K) is one of the most abundant elements in the Earth's crust (2.4% by mass). One out of every 10,000 Potassium atoms is radioactive Potassium-40 (K-40). These each have 19 protons and 21 neutrons in their nucleus. If one of these protons is hit by a beta particle, it can be converted into a neutron. With 18 protons and 22 neutrons, the atom has become Argon-40 (Ar-40), an inert gas. For every 100 K-40 atoms that decay, 11 become Ar-40.
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Potassium is a Block S, Group 1, Period 4 element. The electronic configuration is [Ar] 4s1. In its elemental form potassium's CAS number is 7440-09-7. The potassium atom has a radius of 227.2 .pm and it's Van der Waals radius is 275.pm.
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Potassium is one of the big 8 elements in the Earth's crust, being the seventh most abundant element at about 2.6% by weight. It is a constituent of many silicates including the orthoclase form of feldspar, one of the most abundant minerals on the earth. A silicate with aluminum, KAlSi3O8, forms the mineral microcline, which can be apple green to brown in color.
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Potassium is a very abundant element, ranking seventh among all the elements in the Earth's crust, 2.59% of which is potassium in combined form. Seawater contains 380 parts per million, making potassium the sixth most plentiful element in solution.
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