It is used as an inert shield for arc welding, to pressurize the fuel tanks of liquid fueled rockets and in supersonic windtunnels. Helium gas is used to inflate blimps, scientific balloons and party balloons. Helium is commercially recovered from natural gas deposits, mostly from Texas, Oklahoma and Kansas. This newly formed helium can eventually work its way to the atmosphere through cracks in the crust. An alpha particle can become a helium atom once it captures two electrons from its surroundings. Alpha decay, one type of radioactive decay, produces particles called alpha particles. The earth's atmospheric helium is replaced by the decay of radioactive elements in the earth's crust. This trace amount of helium is not gravitationally bound to the earth and is constantly lost to space. Helium makes up about 0.0005% of the earth's atmosphere. Two Swedish chemists, Nils Langlet and Per Theodor Cleve, independently found helium in clevite at about the same time as Ramsay. He then sent a sample of these gases to two scientists, Lockyer and Sir William Crookes, who were able to identify the helium within it. He exposed the clevite to mineral acids and collected the gases that were produced.
Sir William Ramsay, a Scottish chemist, conducted an experiment with a mineral containing uranium called clevite. The hunt to find helium on earth ended in 1895. This unknown element was named helium by Lockyer. It was hypothesized that a new element on the sun was responsible for this mysterious yellow emission. Sir Norman Lockyer, an English astronomer, realized that this line, with a wavelength of 587.49 nanometers, could not be produced by any element known at the time. Pierre-Jules-César Janssen, a French astronomer, noticed a yellow line in the sun's spectrum while studying a total solar eclipse in 1868. This fact has key implications for the building up of the periodic table of elements.Helium, the second most abundant element in the universe, was discovered on the sun before it was found on the earth. The ordering of the electrons in the ground state of multielectron atoms, starts with the lowest energy state (ground state) and moves progressively from there up the energy scale until each of the atom’s electrons has been assigned a unique set of quantum numbers. It is the Pauli exclusion principle that requires the electrons in an atom to occupy different energy levels instead of them all condensing in the ground state. In the periodic table, the elements are listed in order of increasing atomic number Z. The number of electrons in each element’s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. The configuration of these electrons follows from the principles of quantum mechanics. The chemical properties of the atom are determined by the number of protons, in fact, by number and arrangement of electrons. See also: Atomic Number – Does it conserve in a nuclear reaction? Atomic Number and Chemical PropertiesĮvery solid, liquid, gas, and plasma is composed of neutral or ionized atoms.
It is the electrons that are responsible for the chemical bavavior of atoms, and which identify the various chemical elements. In a neutral atom there are as many electrons as protons moving about nucleus. The total electrical charge of the nucleus is therefore +Ze, where e (elementary charge) equals to 1,602 x 10 -19 coulombs. Total number of protons in the nucleus is called the atomic number of the atom and is given the symbol Z. The nucleus is composed of protons and neutrons. The atom consist of a small but massive nucleus surrounded by a cloud of rapidly moving electrons.
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