What is the atomic mass of an atom that has 6 protons, 6 neutrons, and 6 electrons?
The subatomic particles provide several bits of information about a given element.
The number of protons is equal to the atomic number of the element. For this element having 6 protons makes the atomic number 6 and makes the element Carbon.
The number of protons plus the number of neutrons equals the atomic mass of the element based upon atomic mass units (amus)
For this element 6 protons and 6 neutrons combine to make an atomic mass of 12 amus.
Lastly, the values of protons and electrons tell whether the atom is an ion or neutral. When protons equal electrons the atom is neutral. When protons are greater than neutrons the atom is a positive charge or cation. When the protons are less than the electrons the atom is a negative charge or anion. For this example the Carbon atom has 6 protons and 6 electrons making it neutral.