Question

\[\ce{^24_12Mg}\] and \[\ce{^26_12Mg}\] are symbols of isotopes of magnesium.

(a) Compare the atoms of these isotopes with respect to :
i. the composition of their nuclei
ii. their electronic configurations

(b) Give reasons why the two isotopes of magnesium have different mass numbers.

Answer 1

(a) i.

	\[\ce{^24_12Mg}\]	\[\ce{^26_12Mg}\]
No. of electrons	12	12
No. of protons	12	12
No. of neutrons	24 - 12 = 12	26 - 12 = 14

Hence, the composition of nuclei

\[\ce{_12Mg^24->(P,n),(12+12)_12Mg^26->(p,n)(12+14)}\]

ii. Electronic configuration = 2, 8, 2

(b) Mass numbers of two isotopes of magnesium are different because of the different number of neutrons, i.e. 12 and 14, respectively.