sentence: Isotopes vary in the number of neutrons present in the nucleus.
sentences_before: By this stage the main elements of the atom were clear, plus the discovery that atoms of an element may occur in isotopes.
sentences_after: Although this model was well understood, modern physics has developed further, and present-day ideas cannot be made easy to understand. Some idea of present-day atomic physics can be got from the links in the table below.
concept_name: isotope
headings: Atomic theory Lord Rutherford atomic model
categories: Nuclear physics Chemistry