atom

is: the basic building block of all normal solid, liquid or gas matter. [P7.1]

is: the smallest part of a chemical element that retains the fundamental chemical and physical properties of that element. [P8.1]

extends: over a diameter of approximately [P7.1, P8.1]

has: a dense, positively charged central nucleus with a diameter of order composed of neutrons and positively charged protons, surrounded by a cloud of negatively charged electrons equal in number to the number of protons, according to Rutherford's nuclear model and all 'realistic' models ever since. [P8.1]

has: zero electrical charge overall. [P8.1]

Contrast with ion.