Here's why:

* Normal carbon (carbon-12) has 6 protons and 6 neutrons.

* Carbon-14 has 6 protons and 8 neutrons.

The number of protons defines the element (in this case, carbon). The number of neutrons can vary, creating isotopes of the same element.

This extra neutron in carbon-14 makes it radioactive, meaning it's unstable and decays over time. This decay is used in radiocarbon dating to determine the age of ancient artifacts and fossils.