Final answer:
Neon (Ne) is the element with the core electron configuration 1s²2s²2p⁶. Sodium (Na) follows Neon in the periodic table, adding one electron in the 3s orbital for its valence shell.
Step-by-step explanation:
The element that has the core electrons 1s²2s²2p⁶ is Neon (Ne). This electron configuration represents the complete filling of the 1s and 2s orbitals, as well as the 2p orbital, which corresponds to the electron configuration of Neon. In the context of the periodic table, sodium (Na) is the alkali metal with atomic number 11 and has one additional electron in the 3s orbital beyond Neon's electron configuration, resulting in the electronic structure 1s²2s²2p⁶3s¹. Core electrons are the electrons in an atom that are not in the outermost shell (valence electrons) and correspond to the noble gas configuration of the immediately preceding noble gas, which in the case of sodium is neon ([Ne]).