The atomic number of an atom is equal to the number of ?
A nuclei
B neutrons plus protons
C electrons plus protons
D protons
E neutrons
The correct answer and explanation is:
Correct Answer: D. Protons
The atomic number of an atom is defined as the number of protons in the nucleus of that atom. It is a fundamental property that determines the identity of an element. Each element on the periodic table has a unique atomic number, meaning it has a specific number of protons in its nucleus. For example, hydrogen has an atomic number of 1, which means it has one proton. Carbon has an atomic number of 6, which means it has six protons.
The atomic number is important because it defines the element’s chemical behavior. Elements are arranged on the periodic table in order of increasing atomic number. Since protons carry a positive charge, the number of protons also determines the number of electrons in a neutral atom. Electrons are negatively charged and balance out the positive charge of protons. Although electrons play a role in chemical reactions, the atomic number is based only on protons.
The number of neutrons in an atom can vary, creating different isotopes of the same element. For example, carbon-12 and carbon-14 are both carbon atoms with six protons, but they have six and eight neutrons, respectively. Despite having different mass numbers, both are still carbon because they have the same atomic number.
The nucleus of an atom contains both protons and neutrons, but only protons determine the atomic number. Therefore, while the sum of protons and neutrons gives the mass number, it does not define the atomic number.
In summary, the atomic number equals the number of protons in an atom. It determines the element’s identity and position in the periodic table. This concept is foundational in understanding atomic structure and the organization of elements.