Electron Configuration Chapter 5 Section 3 Electron Configuration

Ground State Electron Configuration The arrangement of electrons in an atom is called the atom’s electron configuration. Electrons in atoms tend to assume the arrangement that gives the atom the lowest possible energy. The stable, lowest-energy arrangement of the electrons is called the elements ground state electron configuration.

Ground State Electron Configuration Three rules describe how electrons can be arranged in an atom’s orbitals The aufbau principle The Pauli exclusion principle Hund’s Rule

The aufbau principle The aufbau principle states that each electron occupies the lowest energy orbital available. You must fill electrons into orbitals from lowest energy to highest energy.

The aufbau principle

The aufbau principle

The Pauli Exclusion Principle Electrons in an orbital can be represented by arrows in boxes. Electrons have spin and can spin in one of two directions (like a top). An arrow pointing up represents an electron spinning in one direction and an arrow pointing down represents an electron spinning in the other direction.

The Pauli Exclusion Principle The Pauli Exclusion Principle states that a maximum of two electrons can occupy a single atomic orbital. These two electrons must have opposite spins.

Hund’s Rule Hund’s Rule states that single electrons with the same spin must occupy each equal-energy orbital before additional electrons with opposite spins can occupy the same orbital. Simplified: We put one electron in each p, d, or f orbital before pairing them up.

Hund’s Rule

Electron Configurations We will now practice writing electron configurations Li Na Cl As

Valence Electrons Valence Electrons are defined as electrons in the atom’s outermost orbitals (highest principle quantum number). These determine the elements chemical properties. For the main group elements, the number of valence electrons is equal to the group number.

Electron Dot Diagrams Electron dot diagrams are pictorial representations of the valence electrons in an element. In writing an atom’s electron dot diagram, dots representing valence electrons are placed one at a time on the four sides of the symbol and then paired up until all are used. An element can have a maximum of 8 electrons in it’s outer shell. This is the most stable form of an atom.