The element chlorine exists mainly as two isotopes

CHEMISTRY · Multi-part · A Level · Chemistry · Atomic structure · Atomic structure

Problem

The element chlorine exists mainly as two isotopes,

^{35}\text{Cl}

and

^{37}\text{Cl}

. A student analyzes a gaseous sample using a mass spectrometer and obtains the data in the table below.

Isotope	Mass (amu)	Relative abundance (%)
$^{35}\text{Cl}$	34.97	75.78
$^{37}\text{Cl}$	36.97	24.22

(a) Calculate the average atomic mass of chlorine for this sample. Show all work, including the handling of units and significant figures. (b) The value you calculated in part (a) differs slightly from the mass listed for chlorine on a standard periodic table. Propose one plausible experimental or natural reason for this discrepancy and explain your reasoning.

Related theory

Subatomic Particles
Atomic Structure
Atomic number, isotopes and isobars
Structure of Atom
Isotopes
The nuclear atom

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