Definition

Noun: - A soft, silver-white, ductile metallic element that is liquid at normal temperatures. It is the most electropositive and alkaline metal. This element is identified by the symbol Cs and has the atomic number 55 on the periodic table.

Usage

The term "atomic number 55" is the formal, scientific identifier for the chemical element cesium (or caesium, chiefly British English). It is used primarily in scientific, technical, and educational contexts to specify the element unambiguously by its fundamental property—the number of protons in its nucleus.

Examples

• Scientific Context:
  • The sample was confirmed to contain atoms of atomic number 55.
  • Atomic number 55, cesium, is used in atomic clocks due to its precise vibrational frequency.

Advanced Usage

• In Periodic Table Classification: The phrase "atomic number 55" categorizes the element definitively within the periodic table, placing it in Group 1 (alkali metals) and Period 6.
• In Nuclear Physics: It specifies the fundamental nuclear charge of the element, which is critical in equations and descriptions of atomic behavior.

Variants and Related Words

• Cesium (Cs) (n): The common name for the element with atomic number 55.
• Caesium (n): The IUPAC and chiefly British English spelling for cesium.
• Alkali Metal (n): The family of elements to which atomic number 55 belongs, characterized by high reactivity and electropositivity.

Synonyms

• Cesium (chiefly North American English)
• Caesium (chiefly British English and IUPAC)

Related Phrases/Idioms

This term is a specific scientific identifier; it does not have idiomatic or phrasal verb uses in everyday language.

Noun

1. a soft silver-white ductile metallic element (liquid at normal temperatures); the most electropositive and alkaline metal