Number of protons in all nucleus, in the atom of an element is always found same and also number of negatively charged electrons are identical in the surrounding electrons. That's why they have same physical properties. But, isotopes in an element have different number of neutrons in each atomic nucleus of it.
There are 16 protons and 16 electrons are found in each atom of element sulphur. sulphur has four stable isotopes- (32) S (95.02%), (33) S (0.75%), (34) S (4.21%) and (36) S. The mass number shown here combines the total number of protons and neutrons (protons are always 16 and left are neutrons). (32) S (95.02%) and (34) S (4.21%) are most common isotopes. Out of these, the prior one contains 16 neutrons and the second one contains 18 neutrons. Both these isotopes have have same chemical properties and they behave identical while reacting with other elements, because of the identical number of electrons in both isotopes. Although, there's small difference in their mass (6.25%) due to the additional number of neutrons in (34) S, they have slightly differently during the chemical reaction.
The different ratios [S.sup.34]/[S.sup.32] of sulphur from different sources is a result of fractionation of their isotopes. A sulphur crystal always incorporate heavier isotope preferentially in order be enriched in heavy isotope than liquid. The slight difference in the ratios can be found in sulphur from volcanic processes and sulphur found in and seawater. Hydrothermal springs (volcanic sulphur) has lower ratio ([S.sup.34]/[S.sup.32]) than seawater's sulphur. Same with other sulphur crystals. Another example is sodium hydroxide (NaOH) reaction with sulphur dioxide (SO2), in which sulphur isotopes are enriched through reflux system. Also in the formation of sodium hydrogen sulfite (NaHSO3), heavier isotopes are attracted and reacted with H2SO4 (sulphuric acid) and form hydrogen sulfate and sulphur dioxide.
Among all other isotopes of sulphur 35S (t1/2 = 87.2 days) has most limited application.
Ratio of 32S and 34S are looked at most often in isotopic studies, due to the large mass differences between isotopes.
The sulphur isotope ratio standard was based on triolite which is 22:22 stated by Bowen and Attendorn in 1997. Still it's reported relative to Cañon Diablo triolite. The new standard was developed by IAEA (International Atomic Energy Agency) because of the scarcity and lackness of homogeneityin Canon Diablo triolite standard. This new standard is used in sample analysis.
There are many processes which reacts the isotopic composition & global cycling of sulphur due to its reactive nature.
Cycling of sulphur includes the weathering of rocks which are eventually deposited into the sea. It is obtained from the sea spray and rained over the land through nature. Cosmogenic 35S and anthropogenic fluxes also comes in the atmosphere. Again, it comes back to the sea
sulphur fractionation occurs by two processes-
1. 34S is concentrated in the compounds with greatest bond strength or highest oxidation state. This is equilibriaum fractionation which occurs in inorganic reaction between sulphur bearing ions, solids and molecules.
2. Occurs by inorganic or biogenic processes, through reduction of sulfate ions. This fractionation takes place due to the bonds of 32S, weaker than 34S, and which results in the depletion of reduced product in 34S up to 73%. Some external factors are responsible for the inorganic reduction fractionation. Due to these factors S-O bonds are weaken and broken. This process is done very slowly low pH and high temperature.
|Z(p)||N(n)||isotopic mass (u)||half-life||nuclear |
|range of natural |
|43mS||319(5) keV||480(50) ns||(7/2-)|
|47S||16||31||47.00859(86)#||20# ms [>200 ns]||3/2-#|
|48S||16||32||48.01417(97)#||10# ms [>200 ns]||0+|