Question

1. What particles determine the mass number?

2. Why is mass number always a whole number?

3. One isotope of carbon (C) has exactly the same mass number and atomic mass since it was used as the definition of the atomic mass unit (amu). Which isotope is it and what is its atomic mass?

4. What is the approximate mass of one proton? __________amu

5. What is the approximate mass of one neutron? __________amu

Answer 1

The mass number of an atom is determined by the total number of protons and neutrons in its nucleus.

The mass number is always a whole number because it is the sum of the number of protons and neutrons in the nucleus, and both of these particles have a mass of approximately 1 atomic mass unit (amu). Since the mass of an electron is much smaller compared to protons and neutrons, it is not included in the calculation of the mass number.

The isotope of carbon that has the same mass number and atomic mass is carbon-12. Its atomic mass is exactly 12 amu.

The approximate mass of one proton is 1 amu.

The approximate mass of one neutron is also 1 amu.