In the previous blog post, we have discussed on the Group Trends of the Halogens (Group VII elements).
Today, i shall discuss with you an exam-based multiple choice question (MCQ) that test you on your concepts on Group Trends.
Below is an exam-based question send in by one of Sec 3 (2011) O-Level Pure Chemistry student:
Question:
HELLO MR CHUA;
i have chem P2 on friday and i did my school’s past year paper. i asked my teacher this qn, but i don’t understand D:
the ans is D but i don’t understand why (:
Which is most likely to be the most stable compound?
A. NaCl
B. RbCl
C. NaF
D. RbF ? ? ? ? ? ? ? ? ? ? ? ? ? ? ( D )
Suggested Solution:
Before we start, you need to understand which topic they are testing you on. On the first look, it seemed to be question on Chemical Bonding topic.
But once you realised they asked you about “stability” of the compounds, you need to know they are in fact asking about the chemical reactivity of Group I and VII elements, and thus the stability of the ionic compound that is formed.
The most stable compound must be made up of the most reactive metal and the most reactive non-metal for an ionic compound.
Group I Trend: Reactivity increases down the Gp I i.e. Rb is more reactive than Na
Group VII Trend: Reactivity decreases down the Gp VII i.e. F is more reactive than Cl
As such, RbF (D) will be the most stable compound among the four choices.
Hope you are learning something useful here. Feel free to forward this blog post to your friends if you think they can benefit from it. Keep sharing =)