Difference Between Isotope and Ion

Isotope vs Ion
 

Atoms are the small building blocks of all existing substances. There are variations between different atoms. Also, there are variations within the same elements. Isotopes are examples for differences within a single element. Moreover, atoms are hardly stable under natural conditions. They form various combinations between them or with other elements in order to exist. When forming these combinations they may produce ions.

Isotopes

Atoms of the same element can be different. These different atoms of the same element are called isotopes. They are different from each other by having different number of neutrons. Since the neutron number is different, their mass number also differs. However, the isotopes of the same element have the same number of protons and neutrons. Different isotopes present in varying quantities, and this is given as a percentage value called relative abundance. For example, hydrogen has three isotopes as protium, deuterium and tritium. Their number of neutrons and relative abundances are as follows.

¹H – no neutrons, relative abundance is 99.985%

²H- one neutron, relative abundance is 0.015%

³H- two neutrons, relative abundance is 0%

The number of neutrons a nucleus can hold differs from element to element. Among these isotopes, only some are stable. For instance, oxygen has three stable isotopes, and tin has ten stable isotopes. Most of the time simple elements have the same neutron number as the proton number. But in the heavy elements, more neutrons are there than the protons. The number of neutrons is important to balance the stability of the nuclei. When the nuclei are too heavy, they become unstable and, therefore, those isotopes become radioactive. For example, ²³⁸ U emits radiation and decays to much smaller nuclei. Isotopes may have different properties because of their different masses. For example, they may have different spins, thus their NMR spectra differs. However, their electron number is similar giving rise to a similar chemical behavior.

A mass spectrometer can be used to get information about isotopes. It gives the number of isotopes which an element has, their relative abundances and masses.

Ion

Most of the atoms (except nobel gases) are not stable in nature because they don’t have completely filled valence shells. Therefore, most atoms try to complete the valence shell by obtaining the nobel gas configuration. Atoms do this in three ways.

1. By gaining electrons
2. By donating electrons
3. By s haring electrons

Ions are produced because of the first two methods (gaining and donating electrons). Usually electropositive atoms, which are in s block and d block, tend to form ions by donating electrons. By this means, they produce cations. Most ectronegative atoms which are in the p block like to gain electrons and form negative ions. Usually negative ions are larger compared to the atom and positive ions are smaller. Ions can have a single charge, or multiple charges. For example, group I elements make +1 cations, and group II elements make +2 cations. But there are elements in the d block which can make +3,+4, +5 ions, etc. Since there is a change in the number of electrons when forming an ion, the number of protons is not equal to the number of electrons in an ion. Other than the above described polyatomic ions, there can be polyatomic and molecular ions also. When elemental ions are lost from molecules, polyatomic ions are formed (ex: ClO₃^–, NH₄⁺).