Question

In which of the following sets do all species have the same number of electrons? Co,Co 2+

,Co 3+
Br,Kr 1
​
Sr 2+
C, N 3−
,O 2−
Mg 2+
,Sr 2+
,Ba 2+

Answer 1

The set Mg2+, Sr2+, Ba2+ are all isoelectronic, each possessing the electron configuration of neon (1s2 2s2 2p6) with 10 electrons in total. The size of isoelectronic ions is determined by the number of protons, with greater nuclear charge leading to a smaller radius.

Step-by-step explanation:

Atoms and ions that have the same electron configuration are said to be isoelectronic. Ions and atoms that are isoelectronic will have the same number of electrons. In the provided options, the set Mg2+, Sr2+, Ba2+ all have the same number of electrons, which is the electron configuration of the noble gas neon (Ne), or 1s22s22p6, meaning they are all isoelectronic with neon. This electron configuration indicates that these ions all have 10 electrons. The number of protons affects the size of these ions with the same electronic configuration. The more protons there are, the stronger the nuclear charge, which in turn makes the radius smaller for the series of isoelectronic ions and atoms. In this case, Mg2+ would be the smallest because it has the most protons (12), and Ba2+ would be the largest as it has the least protons (56).

Answer 2

The set containing Mg²⁻, Sr²⁻, and Ba²⁻ includes species that are isoelectronic; they all have the same number of electrons, as they are all two electrons short of the electron counts of Ne, Kr, and Xe respectively.

Step-by-step explanation:

The question is about finding a set of species in which all members have the same number of electrons, meaning they are isoelectronic. To be isoelectronic, species must have electron configurations that are identical. For example, N³⁻, O²⁻, and F⁻ all have the electron configuration of Ne (1s²2s²2p⁶). Therefore, we are looking for a list where every species shares a similar electron configuration and, thereby, their total count of electrons.

Out of the sets provided, the set containing Mg²⁻, Sr²⁻, and Ba²⁻ has species that all have the same number of electrons. Each of these species has 10 electrons less than their neutral atoms since they all have lost 2 electrons to achieve a charge of +2. The neutral atoms Mg, Sr, and Ba are from the second column of the periodic table and, in their neutral forms, would have 12, 38, and 56 electrons respectively. Subtracting 2 from each gives us 10, 36, and 54 electrons for Mg²⁻, Sr²⁻, and Ba²⁻, which are the same numbers of electrons as the noble gases Ne, Kr, and Xe respectively, making them isoelectronic.