* Isotopes: Chlorine has two main isotopes, which are atoms of the same element with different numbers of neutrons.
* Chlorine-35 (³⁵Cl): The most common isotope (about 75% abundance) has 18 neutrons (35 total atomic mass – 17 protons = 18 neutrons).
* Chlorine-37 (³⁷Cl): The less common isotope (about 25% abundance) has 20 neutrons (37 total atomic mass – 17 protons = 20 neutrons).
* Average Atomic Mass: The average atomic mass of chlorine listed on the periodic table is approximately 35.45 amu. This reflects the weighted average of the two isotopes and their relative abundances.
So, while chlorine atoms can have 18 neutrons, it's not the most common case. The average chlorine atom contains slightly more than 18 neutrons due to the presence of the Chlorine-37 isotope.
