Elements with atomic number less than 83 have at least one stable isotopes except technetium (Tc, Z = 41) and promethium (Pm, Z = 61). Elements with atomic number between 84 and 92 (inclusive) are present, but some only as decay products of uranium or thorium. This aspect is discussed in decay families.
Nuclides 2D, 4He, 6Li, 10B, 12C, 14N, 16O, 20Ne, 24Mg, 28Si, 32S, 36Ar, and 40Ca have equal number of protons and neutrons. All other nuclides have more neutrons than protons.
Only 2D, 6Li, 10B, and 14N have equal but odd number of protons and neutrons.
Heavy stable nuclides have more neutrons per proton than light ones have.
In our discussion of radioactive decay families, you have noticed that the stable element of three families is lead (Z = 82), and it has a magic number of protons. The stable nuclide for the fourth family is 209Bi83, and it has a magic number (126) of neutrons. This is the stable nuclide with the highest atomic number.
|Effect of Paring Nucleons|
|Z||N||No. of |
More than half (59%) of stable nuclides have even numbers of protons and neutrons. This fact suggests that pairing of protons and neutrons contributes to the stability of nuclides.
The effect of pairing also affects the abundance of the isotopes in elements, as well as the abundance of a nuclide on a planet, galactic or universal scale.
Nucleon pairing also affects the decay of unstable nuclides.
The sun has 99.9% of the mass of the solar system. Hydrogen atoms contribute 72%, and helium 4He 26% to all atoms in the Sun.
Taking as a whole, the most abundant element of the planet Earth is iron, which is the major component of the earth (molten) core. Additional evidence comes from the many iron meteorites, which are considered debris from outer space. However, the most abundant element of the Earth crust is oxygen in terms of number of atoms, but silicon is the most abundant element by mass.