In atomic theory, what does the atomic number signify?

In atomic theory, what does the atomic number signify?

• A. Total number of electrons
• B. Total number of protons
• C. Total number of neutrons
• D. Mass of the nucleus

Answer: (B)

The atomic number tells you how many protons are in the nucleus. That proton count defines the identity of the element on the periodic table, so it uniquely distinguishes one element from another. In a neutral atom, the number of electrons equals the number of protons, but the atomic number itself is fundamentally the count of protons. The number of neutrons would give you the neutron count and relates to the mass minus the proton number, not the atomic number. The mass of the nucleus depends on both protons and neutrons and isn’t simply the proton count.

The atomic number tells you how many protons are in the nucleus. That proton count defines the identity of the element on the periodic table, so it uniquely distinguishes one element from another. In a neutral atom, the number of electrons equals the number of protons, but the atomic number itself is fundamentally the count of protons. The number of neutrons would give you the neutron count and relates to the mass minus the proton number, not the atomic number. The mass of the nucleus depends on both protons and neutrons and isn’t simply the proton count.