Four elements of the third period have valence configurations (i) $3 s^{1}$ , (ii) $3 s^{2} 3 p^{1}$ , (iii) $3 s^{2} 3 p^{3}$ and (iv) $3 s^{2} 3 p^{5}$ . Which has the highest first ionisation enthalpy? (Data in $kJ mo l^{- 1}$ : Na 496, Al 577, P 1012, Cl 1251.)

A(i)
B(iv)
C(ii)
D(iii)

Answer: B

The configurations correspond to Na, Al, P and Cl respectively. With data values 496, 577, 1012 and 1251 the highest is Cl, configuration (iv). This agrees with the general increase across a period caused by greater effective nuclear charge.

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Four elements of the third period have valence configurations (i) 3s1, (ii) 3s23p1, (iii) 3s23p3 and (iv) 3s23p5. Which has the highest first ionisation enthalpy? (Data in kJ mol−1: Na 496, Al 577, P 1012, Cl 1251.)

Answer: B

More questions on Modern periodic table and classification of elements

Four elements of the third period have valence configurations (i) $3 s^{1}$ , (ii) $3 s^{2} 3 p^{1}$ , (iii) $3 s^{2} 3 p^{3}$ and (iv) $3 s^{2} 3 p^{5}$ . Which has the highest first ionisation enthalpy? (Data in $kJ mo l^{- 1}$ : Na 496, Al 577, P 1012, Cl 1251.)