element: Atomic Number and Mass Number
Atomic Number and Mass Number
Regardless of how many atoms the element is composed of, each atom has the same number of protons in its nucleus, and this is different from the number in the nucleus of any other element. Thus this number, called the atomic number (at. no.), defines the element. For example, the element carbon consists of atoms all with at. no. 6, i.e., all having 6 protons in the nucleus; any atom with at. no. 6 is a carbon atom. By 2016, 118 elements were known, ranging from hydrogen with an at. no. of 1 to oganesson with an at. no. of 118.
Sections in this article:
- Introduction
- Discovery of the Elements
- Evolution of Modern Concepts
- Greek Concept of the Elements
- The Elements through the Ages
- Official Symbols and Names for the Elements
- Properties of the Elements
- Atomic Mass and Atomic Weight
- Isotopes
- Atomic Number and Mass Number
- The Atom
- Bibliography
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2024, Columbia University Press. All rights reserved.
See more Encyclopedia articles on: Chemistry: General