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A helium atom is an atom of the chemical element helium. Helium is composed of two electrons bound by the electromagnetic force to a nucleus containing two protons along with two neutrons, depending on the isotope , held together by the strong force .
The Moon's surface contains helium-3 at concentrations on the order of 10 ppb, much higher than the approximately 5 ppt found in the Earth's atmosphere. [117] [118] A number of people, starting with Gerald Kulcinski in 1986, [119] have proposed to explore the Moon, mine lunar regolith, and use the helium-3 for fusion.
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.
In Earth's atmosphere, the ratio of 3 He to 4 He is 1.343(13) × 10 −6. [5] However, the isotopic abundance of helium varies greatly depending on its origin. In the Local Interstellar Cloud, the proportion of 3 He to 4 He is 1.62(29) × 10 −4, [6] which is ~121 times higher than in Earth's atmosphere.
Phase diagram for Helium-3. "Bcc" indicates a body-centered cubic crystal lattice. An important property of helium-3, which distinguishes it from the more common helium-4, is that its nucleus is a fermion since it contains an odd number of spin 1 ⁄ 2 particles. Helium-4 nuclei are bosons, containing an even number of spin 1 ⁄ 2 particles.
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 ...
The number of protons in an atom (which Rutherford called the "atomic number" [27] [28]) was found to be equal to the element's ordinal number on the periodic table and therefore provided a simple and clear-cut way of distinguishing the elements from each other. The atomic weight of each element is higher than its proton number, so Rutherford ...
Atomicity is the total number of atoms present in a molecule of an element. For example, each molecule of oxygen (O 2) is composed of two oxygen atoms.Therefore, the atomicity of oxygen is 2.