SAT Descriptive Chemistry Problem with Solution

Today I would like to provide a solution to yesterday’s SAT Descriptive Chemistry Problem. Here is the question one more time, followed by an explanation:

Level 2 Descriptive Chemistry Question

Which of the following elements is the least chemically reactive?

A) F
B) S
C) Kr
D) Po
E) Mo

*Solution: The noble gases are the least reactive elements on the periodic table. Krypton, choice (C) is a noble gas.

Remarks: (1) The noble gases are named ‘noble’ because of their reluctance to react with the other elements of the periodic table.

(2) The elements in this problem are shaded on the periodic table below. From top to bottom, they are fluorine, sulfur, krypton, molybdenum, and polonium. Only krypton is a noble gas from this list.

Definitions: Noble gases make up the rightmost column of the periodic table. One of the important characteristics of noble gases is that their valence shell of electrons is full. Having a completed valence shell is the reason for their high stability and unwillingness to interact with other atoms.

A valence shell is the outermost shell of electrons for an atom. Valence shells are normally filled when they have eight electrons. See problem 27 in 320 SAT Chemistry Subject Test Problems for an illustrated analogy about shells.

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