Definition

1. Noun:
   • A chemical element: "atomic number 9" is the scientific term for the chemical element with the number 9 in the periodic table. It is a highly reactive, pale yellow gas at room temperature.
   • A specific element: It refers exclusively to the element fluorine.

Usage

• The term "atomic number 9" is used primarily in scientific, technical, and educational contexts to identify the element fluorine by its fundamental property—the number of protons in its nucleus.
• It is a precise identifier, often used in chemistry and physics to avoid ambiguity.

Examples

• Noun:
  • The periodic table lists fluorine as atomic number 9.
  • Atomic number 9 is essential for the production of many pharmaceuticals.

Advanced Usage

• In compound identification: While "atomic number 9" itself is not used in compounds, the element it denotes (fluorine) is a key component. For example, in discussing fluorocarbons, one might reference that they contain the element with atomic number 9.
• In nuclear contexts: The stability of an isotope can be discussed in relation to its atomic number; for instance, the only stable isotope of atomic number 9 is fluorine-19.

Variants and Related Words

• Fluorine (F): The common name for the element represented by atomic number 9.
  • Fluorine is added to drinking water to prevent tooth decay.
• Fluoride: A compound containing fluorine, often referring to the anion (F⁻).
  • Sodium fluoride is a common ingredient in toothpaste.

Synonyms

• Fluorine: The direct and most common synonym.
• F: The chemical symbol for the element.

Related Phrases

• Element 9: An informal, synonymous phrase.
  • Element 9 is the lightest halogen.
• Group 17, Period 2: Its location in the periodic table, often mentioned alongside its atomic number for full classification.

Noun

1. a nonmetallic univalent element belonging to the halogens; usually a yellow irritating toxic flammable gas; a powerful oxidizing agent; recovered from fluorite or cryolite or fluorapatite