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

The number found in this way is one less than the atomic number.

From Project Gutenberg

Their principal food is the radio-active element, atomic number 109, as yet undiscovered on the planets.

From Project Gutenberg