In the 3rd period, the first ionisation potential is of the order

Question

In the 3rd period, the first ionisation potential is of the order (A) Na > Mg > Al > Si > P (B) Mg > Na > Si > P > Al (C) Na < Mg < Al < Si < P (D) Na < Al < Mg < Si < P

Tardigrade Admin · Accepted Answer

Ionisation potential increases across a period with increasing atomic number. But

M g (1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2})

has higher ionisation enthalpy than

A l (1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{1})

due to stable fully filled orbitals of magnesium. Thus, the correct order is :
1st

I . E (k J m o l^{- 1}) : 496 N a < 577 A l < 737 M g < 786 S i < 1011 P

Q. In the $3^{r d}$ period, the first ionisation potential is of the order

$N a > M g > A l > S i > P$

$M g > N a > S i > P > A l$

$N a < M g < A l < S i < P$

$N a < A l < M g < S i < P$

Q. In the 3rd period, the first ionisation potential is of the order

Na>Mg>Al>Si>P

Mg>Na>Si>P>Al

Na<Mg<Al<Si<P

Na<Al<Mg<Si<P

Ionisation potential increases across a period with increasing atomic number. But Mg(1s22s22p63s2) has higher ionisation enthalpy than Al(1s22s22p63s23p1) due to stable fully filled orbitals of magnesium. Thus, the correct order is : 1st I.E(kJmol−1):496Na​<577Al​<737Mg​<786Si​<1011P​

Q. In the $3^{r d}$ period, the first ionisation potential is of the order

$N a > M g > A l > S i > P$

$M g > N a > S i > P > A l$

$N a < M g < A l < S i < P$

$N a < A l < M g < S i < P$