Isobars are atomic species having the same mass number but different atomic number e.g. ^{210}_{82}Pb, ^{210}_{83}Bi, ^{210}_{84}Po; ^{40}_{18}Ar, ^{40}_{20}Ca etc. they differ in chemical properties, however physical properties related to mass are same

Isotones are atoms having same number of neutrons but different mass number e.g.  ^{30}_{14}Si, ^{31}_{15}P, ^{31}_{16}Si. (All have 16 neutrons).

Isomers (nuclear) are atoms having the same mass number and same atomic number but with different radioactive properties e.g. ^{80}_{35}Br.

The above four terms may be summed up as:

Term No. of Protons No. of Neutrons Mass number Example
Isotopes Same Different Different ^{16}_{8}O, ^{18}_{8}O
Isobars Different Different Same ^{40}_{18}Ar, ^{40}_{18}Ca
Isotones Different Same Different ^{30}_{14}Si, ^{31}_{15}P, ^{32}_{16}S
Isomers Same Same Same ^{80}{35}Br


Isodiaphere: Have same (n – z) or (A – 2z) value


_9 F^{19}

n = 10

z = 9

n – Z = 10 -9 = (1)

A -2Z = 19 -18 = (1)



N = 20

Z = 19

n – Z = 20 -19 = (1)

A – 2Z = 39 -38 = (1)

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