An element X has electron configuration 1s2 2s2 2p6 3s2 3p5. Which of the following statements is correct about the element?
lt has a completely filled p-orbital
lt has 5 electrons in its outermost shell.
lt belongs to group ll on the periodic table
lt is a halogen
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1s2 ( shell 1), 2s2 and 2p6 (shell 2), 3s2 & 3p5 ( shell 3).
the element has 3 shells and therefore can be found in period 3.
K=2 L = 8. M =7 (outermost shell).
the element has 7 valence electrons in it's outermost shell and therefore can be found in group 7. All group 7 elements are halogen.
The number "3" is the last principal shell of the atom. Seeing that 3 has two subshells s and p, we add up the number of electrons in those two subshells to give 7, and that is the number of electrons in the outermost shell (since the outermost shell has principal quantum number 3). Therefore the element is in group 7 (a halogen)
