chemistry questions under atom?

myGod25

3 months ago

An atom of element X has 81 electrons and 124 neutrons.
(a) How many protons has it?
(b) What would you expect the mass number to be

Draw a simple model of an atom to show the position of each of the constituents of the atom


Atom of the same element are alike in every aspect and differ from atoms of other elements. This is one of the ideas from Dalton's atomic theory.
(a) Which modern discovery rendered the idea invalid?
(b) How has the idea been modified by the modern atomic theory?