The phrase “noble gas below krypton on the periodic table” is answered by reading the periodic table as a grid: vertical columns are groups (families) and horizontal rows are periods.
Step-by-step identification
- Interpret “below” correctly. “Below” means directly under in the same column, so the element must be in the same group as krypton.
- Locate krypton (Kr). Krypton is a noble gas in Group 18 (the far-right column) and sits in Period 4.
- Move one period down within Group 18. The element directly below krypton in Group 18 (Period 5) is xenon (Xe).
- Confirm using chemical meaning of “noble gas.” Noble gases have filled valence shells; xenon’s valence shell is complete with \(5s^2 5p^6\), consistent with Group 18 behavior.
Result: The noble gas directly below krypton on the periodic table is xenon (Xe).
A common cross-check is xenon’s atomic number: \(Z = 54\), which comes after krypton’s \(Z = 36\) as the next noble gas down the column.
Group 18 (noble gases) around krypton
| Period | Noble gas (Group 18) | Symbol | Atomic number \(Z\) |
|---|---|---|---|
| 3 | Argon | Ar | \(18\) |
| 4 | Krypton | Kr | \(36\) |
| 5 | Xenon | Xe | \(54\) |
| 6 | Radon | Rn | \(86\) |
Visualization: moving “down the column” from Kr to Xe
Optional confirmation using electron configuration
Krypton ends Period 4 with a filled \(4p\) subshell; the next noble gas down completes the next \(p\) subshell in Period 5. Xenon can be written in condensed form as:
\[ \text{Xe: } [\text{Kr}]\,5s^2\,4d^{10}\,5p^6 \]
The completed \(5p^6\) valence subshell is the hallmark of a noble gas, matching xenon’s placement directly below krypton in Group 18.