Counting nuclear charge for copper How many protons does a neutral copper (Cu) atom contain in its nucleus (i.e., what is its atomic number)?

Introduction / Context:
The atomic number Z equals the number of protons in the nucleus and uniquely identifies an element. Copper is a common engineering metal; knowing Z helps in electronic configuration, X-ray lines, and periodic trends used in materials and electrical engineering.

Given Data / Assumptions:

• Element: copper (chemical symbol Cu).
• Looking for atomic number = number of protons.

Concept / Approach:

For a neutral atom, number of electrons equals number of protons, which equals the atomic number. Copper’s standard atomic number is Z = 29. Isotopes change neutron count, not proton count. Therefore, every copper atom has 29 protons regardless of isotope.

Step-by-Step Reasoning:

Verification / Alternative check:

Spectroscopic notation and electronic configuration of copper [Ar] 3d^10 4s^1 corresponds to 29 electrons in the neutral state, confirming 29 protons in the nucleus.

Why Other Options Are Wrong:

• 2, 9, 11: atomic numbers of He, F, and Na respectively.
• 63: approximate mass number of a common Cu isotope, not proton count.

Common Pitfalls:

Confusing atomic number (protons) with mass number (protons + neutrons).

Final Answer:

29