Isotopes, isobars, isotones
Structure of Atom (School Level) · Chemistry
Study notes
Chlorine has two isotopes: ³⁵Cl (75%) and ³⁷Cl (25%). Calculate its average atomic mass. Step 1: Contribution of ³⁵Cl = 35 × 0.75 = 26.25. Step 2: Contribution of ³⁷Cl = 37 × 0.25 = 9.25. Step 3: Average = 26.25 + 9.25 = 35.5 u. This is why the periodic table shows chlorine as 35.5, not a whole number.