distinguish between nucleon number and proton number

Atoms, Nuclei and Radiation

What is a Nucleus?

Imagine a tiny, super‑dense core inside every atom. This core is the nucleus, made of protons and neutrons. Think of it as the “heart” of the atom. ❤️

Protons, Neutrons and Electrons

• Protons: positively charged, live in the nucleus.
• Neutrons: no charge, also in the nucleus.
• Electrons: negatively charged, orbit the nucleus.

Two Important Numbers

Scientists use two numbers to describe the nucleus:

1. Proton Number (Atomic Number) $Z$ – counts how many protons are in the nucleus. It tells you which element it is. For example, $Z=6$ means the element is carbon.
2. Nucleon Number (Mass Number) $A$ – counts both protons and neutrons. It tells you how heavy the nucleus is. For example, $A=12$ means the nucleus has 12 nucleons.

Why the Difference Matters

Two atoms can have the same $Z$ but different $A$ – they are isotopes. They behave the same chemically but have different masses and sometimes different stability.

Quick Reference Table

Quick Quiz 🎓

What is the nucleon number of an atom with 8 protons and 10 neutrons?

Answer: $A = 8 + 10 = 18$.

Remember

• Proton Number $Z$ = element identity. • Nucleon Number $A$ = total mass of nucleus. • Isotopes share the same $Z$ but different $A$.