⚛️ The nucleus is the tiny, dense centre of an atom that contains protons and neutrons.
💡 Protons carry a positive charge, while neutrons are electrically neutral.
📚 The relative charge of a nucleus is simply the total positive charge contributed by its protons.
The proton number (also called the atomic number) is denoted by \$Z\$ and counts how many protons are in the nucleus.
Each proton contributes a charge of \$e = 1.602 \times 10^{-19}\,\text{C}\$.
Therefore the relative charge of a nucleus is:
\$q = Z \, e\$
Example: A carbon nucleus (Z = 6) has a relative charge of
\$q = 6 \times 1.602 \times 10^{-19}\,\text{C} = 9.612 \times 10^{-19}\,\text{C}\$.
Analogy: Imagine the nucleus as a bustling city.
Each proton is like a resident holding a positive “electric street sign.”
The total number of signs (protons) tells you how many signs the city has, and the sum of all signs gives the city’s overall positive charge.
| Element | Symbol | Proton Number (Z) | Relative Charge \$q\$ (C) |
|---|---|---|---|
| Hydrogen | H | 1 | \$1.602 \times 10^{-19}\$ |
| Carbon | C | 6 | \$9.612 \times 10^{-19}\$ |
| Oxygen | O | 8 | \$1.2816 \times 10^{-18}\$ |
Exam Tip 1: When asked for the relative charge of a nucleus, always write the formula \$q = Z e\$ and substitute the given proton number.
Exam Tip 2: Remember that the charge is always positive for a nucleus because it is made of protons.
Exam Tip 3: Check your units: the result should be in coulombs (C).
Exam Tip 4: If the question gives the relative charge in elementary charge units, simply state the proton number \$Z\$.