* Proper nouns are specific names for people, places, or things. They are always capitalized. Examples: John, London, Mount Everest.

* Elements and gases are general categories. They refer to groups of substances, not specific individuals.

Examples:

* Element: Oxygen (not Oxygen)

* Gas: Helium (not Helium)

However, some names of specific gases *are* proper nouns:

* Laughing gas (a specific name for nitrous oxide)

* Mustard gas (a specific name for a chemical weapon)

Key Takeaway: While specific names of gases can be proper nouns, the general terms "element" and "gas" are not.