Topic of Discussion: Atomic Structure – Isoelectronic Configurations
We have all learned Isotopes in Basic Chemistry syllabus such as the Cambridge Singapore GCE O-Level Chemistry (and other equivalents such as IGCSE, etc).
In Advanced Chemistry syllabus such as the Cambridge Singapore GCE A-Level H2 Chemistry, we need to understand another important term known as Isoelectronic Configurations.
It is defined as:
Species (atoms, ions or even molecules) have the same electronic configurations. i.e. same number of electrons.
Let me give you an example. All the following species have isoelectronic configurations.
N3- nitride ion: 1s22s22p6
F– fluoride ion: 1s22s22p6
Ne neon atom: 1s22s22p6
Na+ sodium ion: 1s22s22p6
If you fine with the above concepts, let’s take a look at a potential exam-based question that i shared with my JC A-Level H2 Chemistry Tuition Classes in Singapore.
Question 1:
Which of the following chemical species has an electronic configuration that is NOT isoelectronic with hydrogen sulfide?
A. Argon gas
B. Ca2+ ion
C. Fluorine gas
D. Oxide ion
Suggested Solution:
Hydrogen sulfide is a covalent molecule with a total of 2(1) + 16 = 18 electrons. Thus, it has an electronic configurations of 1s22s22p63s23p6.
Option A: Argon gas exists as a monatomic element has has 18 electrons. Thus, it has an electronic configurations of 1s22s22p63s23p6 and is isoelectronic with H2S.
Option B: Calcium atom has 20 electrons and Ca2+ ion will thus have 20 – 2 = 18 electrons. Thus, it has an electronic configurations of 1s22s22p63s23p6 and is isoelectronic with H2S.
Option C: Fluorine gas exists as diatomic molecule F2 with a total of 2(9) = 18 electrons. Thus, it has an electronic configurations of 1s22s22p63s23p6 and is isoelectronic with H2S.
Option D: Oxygen atom has 8 electrons and O2- ion will thus have 8 + 2 = 10 electrons. Thus, it has an electronic configurations of 1s22s22p6 and is NOT isoelectronic with H2S.
Thus, answer is (Option D).
I am sure you have learned something useful today.
Feel free to share it with your friends who need help in Advanced Chemistry such as GCE A-Level H2 Chemistry in their Junior Colleges (JC).
Cheers! 🙂