1/3/2024 0 Comments Potassium element card![]() The melting point of potassium is very low for a metal. Chemically, though, that's not a good idea (see "Chemical properties" below). That means that potassium metal can float on water. Its density is 0.862 grams per cubic centimeter, less than that of water (1.00 grams per cubic centimeter). ![]() Potassium is a soft, silvery-white metal with a melting point of 63 ☌ (145 ☏) and a boiling point of 770 ☌ (1,420 ☏). Davy named these two elements after their much older names: potassium for "potash" and sodium for "soda ash." Physical properties A few days later he repeated his experiment with soda ash and produced pure sodium metal. The droplet was the first piece of potassium and sodium ever to be seen by a human.ĭavy had his first success with potassium using this approach on October 6, 1807. He was amazed to see a tiny liquid droplet of metal formed in each case. Then he passed an electric current through the molten (melted) substances. Instead, he melted a sample of potash and a sample of soda ash. He decided to use no water in his experiment. Then Davy thought of another way to separate potash and soda ash into their elements. The free element can never be recovered by this method. But as soon as the element is formed, it reacts immediately with the water. Both elements are freed when an electric current is passed through a water solution of potash or soda ash. What Davy did not know was how active the elements potassium and sodium are. The first method that Davy tried was to pass an electric current through a water solution of one compound or the other. They tried to think of ways to break these compounds down into their elements. It was not until the eighteenth century that chemists understood the difference between potash (vegetable alkali) and soda ash (mineral alkali).īy the late 1700s, chemists were reasonably sure that both potash and soda ash contained elements they had never seen. The main difference between them was the source from which they came. For example, they could both be used as cleaning materials. The two materials looked and acted very much alike. The modern chemical name for soda ash is sodium carbonate (Na 2CO 3).įor many centuries, people had trouble telling "vegetable alkali" and "mineral alkali" apart. "Mineral alkali" was also called soda ash. This material was made from certain kinds of rocks. Early humans also knew about a similar substance called mineral alkali. The chemical name for potash is potassium carbonate (K 2CO 3). ![]() Common household lye (such as Drano) is a typical alkali. The word alkali means a strong, harsh chemical that can be used for cleaning. That name comes from the origin of the material ("vegetable" plants that contain wood) and the most important property of the material, alkali. Potash was often called vegetable alkali. It was then recovered by evaporating the water. PRONUNCIATION poe-TAS-see-um Discovery and namingĮarly humans were familiar with potash, a potassium compound that forms when wood burns. However, compounds of potassium have many important applications, the most important of which is as a fertilizer. There are very few uses for potassium as a pure element. (See sidebar on Davy in the calcium entry in Volume 1.) The electrical current breaks the compound into its elements. In electrolysis, an electric current is passed through a molten (melted) compound. Davy used a new method of isolating elements that he had invented, electrolysis. It was first prepared in pure form in 1807 by English chemist Sir Humphry Davy (1778-1829). It always occurs in compounds, combined with other elements. Potassium is so active that it never occurs free in nature. The alkali metals also include lithium, sodium, rubidium, cesium, and francium. The periodic table is a chart that shows how chemical elements are related to one another. The alkali metals are the elements that make up Group 1 (IA) of the periodic table. Note: This article, originally published in 1998, was updated in 2006 for the eBook edition. ![]()
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