Chemistry
Answer
Mass number is slightly less than the actual atomic mass because it is calculated by taking the mass of each proton and neutron as exactly 1 a.m.u. and by neglecting the mass of electrons.
However, the actual atomic mass is determined experimentally and includes the true masses of protons, neutrons and electrons. Since protons and neutrons are each slightly heavier than 1 a.m.u., and electrons also add a very small mass, the actual atomic mass is slightly greater than the mass number.
Related Questions
State the incorrect statement from the list given below:
- Modern atomic theory differs from Dalton's atomic theory with inference to isotopes.
- On supplying energy initially to an atom, an electron may move from K shell to L shell of the atom.
- An atom 'X' having equal no. of protons & neutrons in its atom, has electronic configuration-2, 8, 10.
- Atoms of the same element having atomic mass 39 & 41 respectively, have the same electronic configuration.
Give reasons:
An electron in K shell has the minimum energy.
Give reasons:
Noble gases are almost inert to chemical reactions.
Give reasons:
Nitrogen molecule has no lone pair of electrons, while ammonia molecule has one lone pair.