Match each fundamental atomic structure term with its correct scientific definition.

Atomic number ( $Z$ )The number of protons in the nucleus that defines the chemical identity of an element
Mass number ( $A$ )The total sum of protons and neutrons located inside the nucleus
Valence electronsThe electrons located in the outermost shell that govern chemical bonding and reactivity
IsotopesAtoms of the same element with identical proton counts but different numbers of neutrons

Answer

Atomic number matches the number of protons defining element identity; Mass number matches the sum of protons and neutrons; Valence electrons match the outermost shell electrons involved in bonding; Isotopes match atoms of the same element with differing neutron counts.

Each scientific term corresponds directly to its foundational definition in atomic structure: atomic number represents protons; mass number represents protons plus neutrons; valence electrons are the outermost bonding electrons; isotopes are atoms of the same element varying in neutron number.

Step-by-Step Solution

Define atomic number (

Z

)

Identified as the count of protons in the nucleus, defining elemental identity.

By definition, the number of protons is unique to each element and equals its atomic number.

Define mass number (

A

)

Identified as the sum of protons and neutrons.

Electrons have negligible mass, so the mass number accounts for the heavy nuclear particles.

Define valence electrons

Identified as outermost electrons governing bonding.

Only electrons in the outermost energy level participate in chemical reactions and bond formation.

Define isotopes

Identified as atoms of the same element with different neutron numbers.

Since proton number defines the element, isotopes share chemical properties but have different physical masses due to unequal neutrons.

Key Concept

Core definitions of subatomic particles, nuclear notation, and electron configurations in atomic theory.

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