Room-condition meaning of “gas on the periodic table”
The phrase “first gas on periodic table alphabetically” is most consistently interpreted using the physical state shown on many periodic tables at standard room conditions, approximately \(25^\circ\text{C}\) and \(1\ \text{atm}\). Under those conditions, only a small set of elements exist as gases; most elements are solids, and a few are liquids.
Gas status depends on temperature and pressure. The ordering below uses the common classroom convention of room temperature and 1 atm, matching how periodic tables label element states.
Alphabetical comparison among gaseous elements
The elements that are gases at room temperature include the noble gases (He, Ne, Ar, Kr, Xe, Rn) and several nonmetals (H, N, O, F, Cl). Alphabetical ordering is applied to element names (not symbols).
| Element name (alphabetical) | Symbol | Atomic number | Category (periodic table) | Common form at room temperature |
|---|---|---|---|---|
| Argon | Ar | 18 | Noble gas (Group 18) | Monatomic gas |
| Chlorine | Cl | 17 | Halogen (Group 17) | Diatomic gas, \(\mathrm{Cl_2}\) |
| Fluorine | F | 9 | Halogen (Group 17) | Diatomic gas, \(\mathrm{F_2}\) |
| Helium | He | 2 | Noble gas (Group 18) | Monatomic gas |
| Hydrogen | H | 1 | Nonmetal | Diatomic gas, \(\mathrm{H_2}\) |
| Krypton | Kr | 36 | Noble gas (Group 18) | Monatomic gas |
| Neon | Ne | 10 | Noble gas (Group 18) | Monatomic gas |
| Nitrogen | N | 7 | Nonmetal | Diatomic gas, \(\mathrm{N_2}\) |
| Oxygen | O | 8 | Nonmetal | Diatomic gas, \(\mathrm{O_2}\) |
| Radon | Rn | 86 | Noble gas (Group 18) | Monatomic gas |
| Xenon | Xe | 54 | Noble gas (Group 18) | Monatomic gas |
Result
Argon is the alphabetically earliest element among those that are gases at room temperature, so argon (Ar) is the first gas on the periodic table alphabetically.
Visualization of the alphabetical set of gases
Common source of confusion
“Gas” can be interpreted as “noble gas” only; the noble-gas subset is He, Ne, Ar, Kr, Xe, Rn under room conditions, and argon remains alphabetically earliest within that group.