Question

What is the reason for an element to have atoms with differing mass numbers?

Answer 1

• Mass number(A)- The number of protons and neutrons combine to give us the mass number of an atom.
• Atomic number(Z)- The total number of protons in the nucleus of an atom gives us the atomic number of that atom.
• Isotopes- Atoms of an element having the same atomic number but a different mass number are known as isotopes.
• Protons are positively charged subatomic particles present in the nucleus of an atom.
• Neutrons are neutral subatomic particles present in the nucleus of an atom.
• Example- Hydrogen has three isotopes namely hydrogen, deuterium, and tritium.
• Hydrogen has 1 proton, Z=1, A=1.
• Deuterium has 1 proton and 1 neutron, Z=1, A=2.
• Tritium atom has 1 proton and 2 neutrons, Z=1, A=3.
• In these atoms atomic number is 1 while the mass number is changing.

Hence, an element can have different mass numbers in its atoms due to the different number of neutrons present in it.