atomic number

[ uh-tom-ik nuhm-ber ]

noun

1. the number of positive charges or protons in the nucleus of an atom of a given element, and therefore also the number of electrons normally surrounding the nucleus. : at. no.; : Z

atomic number

noun

1. the number of protons in the nucleus of an atom of an element at. no. Z Also calledproton number

atomic number

1. The number of protons in the nucleus of an atom. In electrically neutral atoms, this number is also equal to the number of electrons orbiting about the atom's nucleus. The atomic number of an element determines its position in the Periodic Table, and is usually denoted by the letter Z and written as a subscript before an element's symbol, as in 92 U.

atomic number

1. The number of protons or electrons normally found in an atom of a given chemical element . The higher the atomic number, the heavier the atom is. In a neutral atom, the number of protons and electrons is the same. ( See atomic weight and periodic table of the elements .)

Word History and Origins

Origin of atomic number¹

First recorded in 1815–25

Example Sentences

Thus, they exposed the secrets of this extremely rare lanthanide, whose atomic number is 61, in a series of meticulous experiments.

From Science Daily

In HAADF-STEM images, signal intensity correlates with the square of the atomic number, making it particularly useful for analyzing heavy elements.

From Science Daily

Lighter elements -- generally those with an atomic number of 20 or lower on the periodic table -- often have an equal number of protons and neutrons.

From Science Daily

And for the individual metals the team could detect, the star also displayed sharply differing abundances for elements with odd and even atomic numbers—a telltale sign of a pair-instability supernova.

From Science Magazine

Katie Hafner: Uranium is the last of the naturally occurring elements on the periodic table, with an atomic number of 92.

From Scientific American