Atomic structure – Determining atomic number: The atomic number of an atom is defined as the count of which subatomic particle in the nucleus?

Introduction / Context:
The atomic number uniquely identifies a chemical element. It distinguishes elements across the periodic table and determines the arrangement of electrons in neutral atoms.

Given Data / Assumptions:

• A neutral atom has equal numbers of protons and electrons.
• Neutrons may vary, producing isotopes without changing the element identity.

Concept / Approach:
Atomic number Z is defined as the number of protons in the nucleus. Protons carry positive charge and establish the element identity. Electron count can change in ions without altering Z. Neutron count N contributes to mass number A = Z + N, not to atomic number.

Step-by-Step Solution:
Recall definition: Z = number of protons.Select the option that states protons.

Verification / Alternative check:
Hydrogen has Z = 1 because it has one proton; carbon has Z = 6, oxygen Z = 8, etc. Isotopes like C-12 and C-14 differ in neutrons but both have Z = 6.

Why Other Options Are Wrong:

• Electrons: vary in ions; not the defining number.
• Neutrons or protons plus neutrons: define isotopes and mass number, not element identity.
• Neutrons minus protons: not a standard definition.

Common Pitfalls:
Confusing atomic number with mass number; forgetting that ions still retain the same atomic number as the neutral atom of the element.

Final Answer:
Protons