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In this situation, we have two 6z electrons – with coordinates r1 and r2 – orbiting a nucleus with. r charge Z = 2located at the point R. Now, for the hydrogen. atom we were able to ignore the motion of the nucleus by trans-forming to the center of mass.
(An atomic mass unit is defined as 1/12th the mass of a \(^{12}C\) nucleus.) In atomic mass units, the mass of a helium nucleus ( A = 4 ) is approximately 4 u. A helium nucleus is also called an alpha ( α ) particle.
The missing mass is the binding energy of the atom (almost all of that energy is in the nucleus). By expressing the mass defect in MeV/c2 (using 1 u = 931.5 MeV/c2), one gets a direct reading of the binding energy in MeV. For example with carbon-12, the mass defect of 0.098931 u converts to 92.15 MeV/c2. This corresponds to a binding energy of
The total amount of energy released for each conversion of four hydrogen nuclei into a helium nucleus is about 10 million times more than is produced by the chemical reaction when hydrogen combines with oxygen and burns to form water.
In addition, the helium nucleus contains two neutrons, particles with a mass comparable to that of the proton but with no electric charge. Moving around this nucleus are two electrons, so the total net charge of the helium atom is also zero (Figure \(\PageIndex{3}\)).
Write and interpret symbols that depict the atomic number, mass number, and charge of an atom or ion; Define the atomic mass unit and average atomic mass; Calculate average atomic mass and isotopic abundance
21 lis 2020 · Atomic mass of Helium is 4.0026 u. The atomic mass is the mass of an atom. The atomic mass or relative isotopic mass refers to the mass of a single particle, and therefore is tied to a certain specific isotope of an element.
