as the number of protons is not equal to electrons. It is anion (negatively charged) with charge equal to excess electrons = – = . Symbol is . Note : Before using the notation A Z X, find out whether the species is a neutral atom, a cation or an anion.
If it is a neutral atom, equation ( . ) is valid, i.e., number of protons = number of electrons = atomic number. If the species is an ion, determine whether the number of protons are larger (cation, positive ion) or smaller (anion, negative ion) than the number of electrons. Number of neutrons is always given by A–Z, whether the species is neutral or ion.
. . Drawbacks of Rutherford Model As you have learnt above, Rutherford nuclear model of an atom is like a small scale solar system with the nucleus playing the role * Classical mechanics is a theoretical science based on Newton’s laws of motion. It specifies the laws of motion of macroscopic objects.
of the massive sun and the electrons being similar to the lighter planets. When classical mechanics * is applied to the solar system, it shows that the planets describe well-defined orbits around the sun. The gravitational force between the planets is given by the expression G. m m r where m and m are the masses, r is the distance of separation of the masses and G is the gravitational constant.
The theory can also calculate precisely the planetary orbits and these are in agreement with the experimental measurements. The similarity between the solar system and nuclear model suggests that electrons should move around the nucleus in well defined orbits. Further, the coulomb force (k q q / r where q and q are the charges, r is the distance of separation of the charges and k is the proportionality constant) between electron and the nucleus is mathematically similar to the gravitational force. However, when a body is moving in an orbit, it undergoes acceleration even if it is moving