Definition

1. Noun:
   • A unique identifier for a chemical element: The atomic number is the number of protons found in the nucleus of an atom of that element. It defines the element's identity and its position in the periodic table.

Usage

• The is a fundamental property of an element. It is always an integer and is represented by the symbol Z.
• In a neutral atom (with no electric charge), the also equals the number of electrons orbiting the nucleus.
• The increases from left to right and top to bottom in the standard periodic table.

Examples

• Noun:
  • Hydrogen has an atomic number of 1, meaning each hydrogen atom has one proton.
  • The atomic number of carbon is 6.
  • Elements are arranged in the periodic table in order of increasing atomic number.

Advanced Usage

• "Atomic number Z": Often written as "atomic number (Z)" in scientific literature to distinguish it from the mass number (A).
  • The isotope is defined by its atomic number (Z) and mass number (A).
• Determining Element Identity: The solely determines what element an atom is, regardless of the number of neutrons or electrons.
  • Changing the atomic number creates a different element.

Variants and Related Words

• Proton number: A synonym for .
• Mass number (A): The total number of protons and neutrons in an atom's nucleus. This is different from the .
• Element: A substance whose atoms all have the same .

Synonyms

• Proton number

Notes

• The is not the same as the atomic mass or atomic weight.
• The concept of the was developed in the early 20th century and resolved inconsistencies in Mendeleev's original periodic table, which was based on atomic weights.

Noun

1. the order of an element in Mendeleyev's table of the elements; equal to the number of protons in the nucleus or electrons in the neutral state of an atom of an element