the concept of an atom as a central positively charged nucleus consisting of protons and neutrons surrounded by a number of electrons. The number of electrons is equal to the number of protons: the whole entity is thus electrically neutral
atomic structure in American English
Physics
a conventionalized, hypothetical concept of an atom, regarded as consisting of a central, positively charged nucleus and a number of negativelycharged electrons revolving about it in various orbits: the number and arrangement of the electrons vary in the different elements