follow Dictionary.com

How Well Do You Know English Slang?

mass number

in nuclear physics, the sum of the numbers of protons and neutrons present in the nucleus of an atom. The mass number is commonly cited in distinguishing among the isotopes of an element, all of which have the same atomic number (number of protons) and are represented by the same literal symbol; for example, the two best known isotopes of uranium (those with mass numbers 235 and 238) are designated uranium-235 (symbolized 235U) and uranium-238 (238U).

Learn more about mass number with a free trial on Britannica.com
Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
Cite This Source

Word of the Day

Word Value for atomic

10
12
Scrabble Words With Friends

Nearby words for atomic mass number