How many protons does an atom with an atomic number of 23 and a mass of 51 have?
23 Protons and 28 Neutrons. The atomic number is always equal to the number of protons in an element. The element is vanadium (symbol V). Any atom with 23 protons is be vanadium, but some vanadium atoms will have more or less than 28 neutrons. The mass number is the sum of the number of protons and neutrons together, and this can vary for the same element (called isotopes). To find the number of neutrons, just subract the atomic number from the mass number.