What does the 4 stand for in helium-4?
Answers
Answer:
The 4 in helium-4 represents the atomic mass of one atom of the helium-4 element. The mass number is equal to the total number of protons and neutrons in the nucleus of the atom.
Explanation:
The helium atom is the second simplest atom (hydrogen is the simplest), but the extra electron introduces a third "body", so the solution to its wave equation becomes a "three-body problem", which has no analytic solution. However, numerical approximations of the equations of quantum mechanics have given a good estimate of the key atomic properties of helium-4, such as its size and ionization energy.
The size of the 4He nucleus has long been known to be in the order of magnitude of 1 fm. In an experiment involving the use of exotic helium atoms where an atomic electron was replaced by a muon, the nucleus size has been estimated to be 1.67824(83) fm.
The nucleus of the helium-4 atom is identical to an alpha particle. High-energy electron-scattering experiments show its charge to decrease exponentially from a maximum at a central point, exactly as does the charge density of helium's own electron cloud. This symmetry reflects similar underlying physics: the pair of neutrons and the pair of protons in helium's nucleus obey the same quantum mechanical rules as do helium's pair of electrons (although the nuclear particles are subject to a different nuclear binding potential), so that all these fermions fully occupy 1s orbitals in pairs, none of them possessing orbital angular momentum, and each canceling the other's intrinsic spin. Adding another of any of these particles would require angular momentum, and would release substantially less energy (in fact, no nucleus with five nucleons is stable). This arrangement is thus energetically extremely stable for all these particles, and this stability accounts for many crucial facts regarding helium in nature.
Find the attachment below for the diagram of helium 4 isotope.