Isobars

Isotopes are chemically same and physically different. But the converse is true in isobars. That is isobars are elements, which are chemically different but physically same. So, isobars are atoms of different elements having the same atomic mass but different atomic number. Since their number of electrons is different, their chemical properties are different. The light nuclei have unstable isobars. Heavy nuclei have stable isobars and these occur in pairs. Suppose the number of protons of one isobar matches with that of another they are called as mirror-nuclides of each other.

Examples of isobars are

Since isobars are different elements they appear in different places in the periodic table.

Isotones

Isotones are elements having the same number of neutrons. Examples of isotones are Chlorine - 37 and Potassium - 39. Both have 20 neutrons in their nuclei.