Definition

Noun: * A white trivalent metallic element; sometimes classified in the rare earth group; occurs in the Scandinavian mineral thortveitite: This is the chemical element with the atomic number 21, known as Scandium (Sc). It is a soft, lightweight, silvery-white metal.

Usage

• The term 'atomic number 21' is the definitive, systematic identifier for the element scandium in scientific contexts, particularly in chemistry and physics. It refers specifically to the number of protons in the nucleus of one atom of this element.
• Example: "The periodic table lists atomic number 21 between calcium (20) and titanium (22)."
• Example: "Atomic number 21 corresponds to the element scandium."

Advanced Usage

• In technical writing, 'atomic number 21' is used for unambiguous identification, especially in databases, indices, or when discussing periodic trends.
• Example: "Elements with atomic number 21 and higher begin to fill the d-orbitals."

Variants and Related Words

• Scandium (Sc): The common name for the element identified by atomic number 21.
• Rare-earth element: A classification group to which scandium is often associated due to similar chemical properties and occurrence, though it is not a lanthanide.

Synonyms

• Scandium
• Sc (the chemical symbol)

Notes on Meaning

The term 'atomic number 21' has a single, precise scientific meaning: it is the unique identifier for the element scandium based on its proton count. All descriptive properties (white, trivalent, metallic, occurrence in thortveitite) are characteristics of that specific element.

Noun

1. a white trivalent metallic element; sometimes classified in the rare earth group; occurs in the Scandinavian mineral thortveitite