Electron Shells Main Concept: - The electronic structure of the atom can be described using an electron configuration that reflects the concept of electrons in quantized energy levels or shells; the energetics of the electrons in the atom can be understood by consideration of Coulomb’s law.

Which has more potential energy? Why? Model of Shells and Subshells Electron Shells Core Electrons vs Valence Electrons Which has more potential energy? Why? Model of Shells and Subshells Shielding What causes it? What happens?

- Electron configurations: a model to show distribution of electrons in an atom or ion. - Each electron in an atom has a different ionization energy, explained by Coulomb’s law.

- electrons can be thought of as being in “shells” and “subshells,” - Shown by relatively close ionization energies of some groups of electrons - Inner electrons = core electrons - outer electrons = valence electrons

- Core electrons are generally closer to the nucleus than valence electrons - They “shield” valence electrons from the full electrostatic attraction of the nucleus - This can be used with Coulomb’s law to explain/rationalize/ predict relative ionization energies

Shielding Effect

- Differences in electron-electron repulsion are responsible for differences in energy between electrons in different orbitals in the same shell

Question: Using Coulomb’s law, how and why would the first ionization energies of sodium and potassium be different? Using Coulomb’s law, how and why would the first ionization energies of sulfur and chlorine be different?