The first ionization enthalpies of Na, Mg and | vedclass

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(C) $Na, Mg, Al$ and $Si$ belong to the $3^{rd}$ period of the periodic table.Generally,the first ionization enthalpy increases across a period due to

Vedclass · Accepted Answer

$575$

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(C) $Na, Mg, Al$ and $Si$ belong to the $3^{rd}$ period of the periodic table.Generally,the first ionization enthalpy increases across a period due to an increase in effective nuclear charge.However,$Mg$ $(3s^2)$ has a fully-filled $s$-orbital,making it more stable than $Al$ $(3s^2 3p^1)$.Therefore,the first ionization enthalpy of $Al$ is lower than that of $Mg$ but higher than that of $Na$.Given values: $Na = 496 \ kJ \ mol^{-1}$,$Mg = 737 \ kJ \ mol^{-1}$,$Si = 786 \ kJ \ mol^{-1}$.The value for $Al$ must be between $496$ and $737 \ kJ \ mol^{-1}$.Thus,the correct value is $575 \ kJ \ mol^{-1}$.

The first ionization enthalpies of $Na, Mg$ and $Si$ are respectively $496, 737$ and $786 \ kJ \ mol^{-1}$. What would be the first ionization enthalpy of $Al$ in $kJ \ mol^{-1}$?

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