Question

how do you explain fractional atomic weight (35.5)of chlorine

Answer 1

Hi friend
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Your answer
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Many elements have isotopic forms. In that case, when an element has more than form its atomic mass is taken as the average atomic mass of its isotope.

For example,
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Chlorine has two isotopic forms : -

1) Chlorine - 35

2) Chlorine - 37


In a mixture of both the isotopes of chlorine , 75% is Cl-35 and 25% is Cl-37 .

Then,
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Fractional atomic mass of Chlorine : -

$(35 \times \frac{75}{100} ) + (37 \times \frac{25}{100} ) \\ \\ = > \frac{105}{4} + \frac{37}{4} \\ \\ = > \frac{142}{4} \\ \\ = > 35.5 \: u \:$
HOPE IT HELPS