# Three dements have the electron configurations 1s^2 2s^2 2p^6 3s^2 3p^5, 1s^2 2s^2 2p^8 3s^2 3p^8...

## Question:

Three elements have the electron configurations {eq}1s^2 2s^2 2p^6 3s^2 3p^5, 1s^2 2s^2 2p^8 3s^2 3p^8 4s^2 {/eq}, and {eq}[Ar]4s^2 3d^{10} 4p^2 {/eq}.

The first ionization energies of these elements (not in the same order) are 0.761. 0.590. and 1.256 MJ/mol. The atomic radii are 197.99. and 122 pm.

Identity the three elements, and match the appropriate values of ionization energy and atomic radius to each configuration.

## Chemical Periodicity:

The electron configuration of an atom or ion describes how electrons are distributed in its atomic orbitals. The Aufbau or building up principle dictates the order of how electrons fill the shells and subshells of the atom by filling up the orbital with the lowest energy first before the ones with the higher energy. Atomic radii decrease across a period and increase down a group in the periodic table. The trend of the first ionization energy increase across a period and decrease down a group in the periodic table. Elements that have the tendency to form cations have low first ionization energy.

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The three elements that correspond to the electron configurations below are:

{eq}1s^2 2s^2 2p^6 3s^2 3p^5 {/eq} - chlorine (Cl)

{eq}1s^2 2s^2...