The reactivity of an atom arises from a. the average distance of the outermost electron shell from the nucleus. b. the existence of unpaired electrons in the valence shell. c. the sum of the potential energies of all the electron shells. d. the potential energy of the valence shell.

Verified step by step guidance

1. Identify that the reactivity of an atom primarily depends on its electron configuration, particularly the electrons in the outermost shell, known as the valence electrons.
2. Understand that the presence of unpaired electrons in the valence shell makes an atom more reactive. These unpaired electrons can easily form bonds with other atoms, either by sharing electrons (covalent bonds) or by transferring electrons (ionic bonds).
3. Recognize that the average distance of the outermost electron shell from the nucleus (option a) affects the size of the atom but not directly its reactivity.
4. Acknowledge that the sum of the potential energies of all electron shells (option c) and the potential energy of the valence shell (option d) relate to the atom's overall energy state but do not directly determine reactivity like unpaired electrons do.
5. Conclude that the correct answer is b. the existence of unpaired electrons in the valence shell, as this is the factor that directly influences an atom's ability to interact and bond with other atoms.

Key Concepts

Valence Electrons

Valence electrons are the electrons located in the outermost shell of an atom. They play a crucial role in chemical bonding and reactivity, as they are the electrons that can be gained, lost, or shared during chemical reactions. The number of valence electrons determines how an atom interacts with others, influencing its reactivity.

Electron Configuration

Electron configuration refers to the distribution of electrons in an atom's electron shells and subshells. This arrangement affects an atom's chemical properties and reactivity. Atoms with unpaired electrons in their valence shell are generally more reactive, as they seek to achieve a stable electron configuration through bonding.

Potential Energy in Electron Shells

The potential energy of electrons in an atom is influenced by their distance from the nucleus and their arrangement in shells. Electrons in higher energy levels (farther from the nucleus) have greater potential energy. Understanding this concept helps explain why certain atoms are more reactive, as they may have unpaired electrons or higher energy states that favor chemical interactions.