Atom A constituent of matter consisting of z negatively charged electrons bound predominantly by the Coulomb force to a tiny, positively charged nucleus consisting of Z protons and (A – Z) neutrons. Z is the atomic number, and A is the mass or nucleon number. The atomic mass unit is u = 1.6605397 x 10-24
Bohr’s model of the atom Neil Bohr in 1913 observed that basic features of Rutherford’s atomic model namely presence of nucleus and revolving electrons were correct but that the electrons revolved round the nucleus in certain allowed circular orbits and that the electrons did not radiate and therefore its energy remained constant. However, the electron
ATOMS Law of constant composition: This states that “A chemical compound (if pure) always contains the same elements combined together in the same proportion by mass regardless of bow the compound is prepared or from where it is obtained”. Law of conservation of mass: This is defined as “In every chemical reaction, the total mass