Periodic Trends

AP Chemistry· difficulty 4/5

Among Na, Mg, Al, and Si, the atom with the LARGEST first ionization energy is

  • A

    Si (highest ZeffZ_{eff} across the period)

  • B

    Na (lowest ZeffZ_{eff})

  • C

    Al (3p electron easier to remove)

  • D

    Mg (filled 3s subshell stability)

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Explanation

Across period 3, IE generally rises with ZeffZ_{eff}, but Mg (3s23s^2) and P (3p33p^3) have anomalously high IEs from filled/half-filled stability. Among Na, Mg, Al, Si: Mg > Si > Al > Na. (Al has a 3p electron easier to remove than Mg's filled 3s.)

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