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The combined first four ionization energies of lead exceed those of tin, Lead's lighter carbon group congeners form stable or metastable allotropes with the tetrahedrally coordinated and covalently bonded diamond cubic structure.
The energy levels of their outer s- and p-orbitals are close enough to allow mixing into four hybrid sp orbitals.
Uranium–lead dating and lead–lead dating on this meteorite allowed refinement of the age of the Earth to 4.55 billion ± 70 million years.
Apart from the stable isotopes, which make up almost all lead that exists naturally, there are trace quantities of a few radioactive isotopes.
Lead has a magic number of protons (82), for which the nuclear shell model accurately predicts an especially stable nucleus.
Lead-208 has 126 neutrons, another magic number, which may explain why lead-208 is extraordinarily stable.
The Holsinger meteorite, the largest piece of the Canyon Diablo meteorite.
It is particularly problematic in children: even if blood levels are promptly normalized with treatment, permanent brain damage may result. The combined first and second ionization energies—the total energy required to remove the two 6p electrons—is close to that of tin, lead's upper neighbor in the carbon group.
This is unusual; ionization energies generally fall going down a group, as an element's outer electrons become more distant from the nucleus, and more shielded by smaller orbitals.
The similarity of ionization energies is caused by the lanthanide contraction—the decrease in element radii from lanthanum (atomic number 57) to lutetium (71), and the relatively small radii of the elements after hafnium (72).
This is due to poor shielding of the nucleus by the lanthanide 4f electrons.
Lead is a chemical element with symbol Pb (from the Latin plumbum) and atomic number 82.