The atomic number is ALWAYS equal to the number of protons; the mass number is equal to the number of protons & neutrons combined

The atomic number is ALWAYS equal to the number of protons; the mass number is equal to the number of protons & neutrons combined.

Element 6, which is carbon, has several isotopes (forms of an element with varying numbers of neutrons).

The most common isotope of carbon is carbon-12, which has 6 protons, 6 neutrons, and 6 electrons. Its mass number is 12 (6 protons + 6 neutrons = 12). Since electrons are so tiny, their mass is generally disregarded (think about it like this: if a 12 lb. dog has 6 fleas on it, how much does the dog weigh? Basically 12 lbs).

Another isotope of carbon, which seems to be the one you are referencing, has 6 protons, 8 neutrons, and 6 electrons. This is called carbon-14, and its mass number is 14.

The number of electrons stays the same, because adding or subtracting electrons does not change the atom's mass- it changes the atom's charge, making it either positive (by subtracting electrons) or negative (by adding electrons). These are called ions. Atoms that have a greater number of electrons than protons are called anions, and have a negative charge. Atoms with fewer electrons than protons are called cations, and have a positive charge. Hope this helps!