Helium-4.
If you think to tritium (hydrogen-3) the mass number is 3.If you think to helium-4 the mass number is 4.
A helium isotope with an atomic mass of 6 would have 2 protons, as all helium atoms have 2 protons. To find the number of neutrons, subtract the number of protons from the atomic mass. So for this isotope, 6 (atomic mass) - 2 (protons) = 4 neutrons.
The mass number of an isotope is the sum of its protons and neutrons. In this case, the isotope of chlorine has 25 protons and 17 neutrons. Therefore, the mass number is 25 + 17 = 42. Thus, the mass number of this isotope of chlorine is 42.
It isn't, as such. Isotopes of the same element have different numbers of neutrons, and neutrons have a mas of one atomic mass unit (amu). So isotopes have different atomic masses, but being told the number of neutrons any isotope has, will not enable you to say what element or atomic mass it had, unless you remembered the details for every single isotope. Even then different elements can have the same number of neutrons. Isotopes do get named after their atomic mass however - uranaium 235 has an atomic mass of 235, for instance.
The mass number of an isotope is the sum of its protons and neutrons. For oxygen, which has 8 protons, an isotope with nine neutrons would have a mass number of 8 (protons) + 9 (neutrons) = 17. Therefore, the mass number of this oxygen isotope is 17. This isotope is known as oxygen-17.
Neodymium, Nd, has an isotope with a mass number of 144. Samarium, Sm, also has an isotope with a mass number of 144.
The isotope with the longest half life (Rf-267) has the mass number 267.Each isotope has a specific mass number.
Most helium has a mass number of 4. The rare 3He isotope has a mass number of 3. The mass number is the integer total of protons and neutrons for a given isotope. For example radioactive carbon-14 has a mass number of 14, while carbon-12 (the most common stable form) has a mass number of 12.
An isotope of indium has 77 protons and 115 neutrons. What is the mass number of this isotope
Subtract the atomic number of the isotope from its atomic mass number to obtain the number of neutrons in an isotope.
Atomic Mass (of an isotope) - number of protons (of an isotope) = number of neutrons (of an isotope)
The mass number of an isotope is the sum of its protons and neutrons. Oxygen has an atomic number of 8, meaning it has 8 protons. If the isotope has 9 neutrons, the mass number would be 8 protons + 9 neutrons = 17. Therefore, the mass number of this oxygen isotope is 17.