Schematically show the number of electrons in the various...

Schematically show the number of electrons in the various subshells of an atom with the electronic shell structure $1 s^{2} 2 s^{2} 2 p^{4}$ and an atomic weight of $21 .$ Indicate how many protons and neutrons there are in the nucleus. Is this atom chemically reactive, and why?

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Key Concepts

Electron Configuration

This concept describes how electrons are distributed in an atom’s orbitals or subshells (such as s, p, d, and f) following principles like the Pauli exclusion principle and Hund’s rule. Understanding the electron configuration—as in the given arrangement 1s² 2s² 2p?—helps determine the total number of electrons in the atom and influences physical and chemical properties.

Atomic Structure (Protons and Neutrons)

Atomic structure involves the composition of an atom's nucleus, which contains protons and neutrons, and electrons orbiting the nucleus. The number of protons equals the number of electrons in a neutral atom and defines the atomic number. The difference between the atomic weight (mass number) and the atomic number gives the number of neutrons, which is important for understanding isotopic variation and nuclear stability.

Chemical Reactivity and Valence Electrons

Chemical reactivity is largely determined by the number and arrangement of electrons in the outermost shell (valence electrons). Atoms with incomplete valence shells, such as those with 6 valence electrons in the 2p? configuration, tend to be chemically reactive because they tend to gain, lose, or share electrons to achieve a more stable electron configuration, often resembling that of a noble gas.

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