Electron Configurations

Energy Levels, Sublevels, and Orbitals Principal energy levels – n, assigned values 1- 7 (Like floors in a hotel) Energy sublevels- s, p, d, f (Type of suite in a hotel) s sublevel – 1 orbital p sublevel – 3 orbitals d sublevel – 5 orbitals f sublevel – 7 orbitals Orbitals – Two electrons per orbital (Two people per room) (Orbitals are the number of rooms in a suite)

Electron Configurations Electron configuration – the arrangement of electrons in an atom. Example Sodium (Na) – Three rules determine electron configurations the Aufbau Principle, the Pauli Exclusion Principle Hund’s rule 1s22s22p63s1

The Aufbau Principle Each electron occupies the lowest energy orbital available Like filling the hotel from the bottom up Which should we fill first, the lowest or highest energy orbital?

Aufbau Diagram Which has a lower energy level 4s or 3d orbitals?

Filling the Orbitals in the correct order

Orbitals in the Periodic Table

Pauli Exclusion Principle A maximum of two electrons may occupy a single orbital Like only two people sharing one hotel room How many electrons are found in an orbital?

Hund’s Rule If two or more orbitals of equal energy are available, electrons will occupy them singly with the same spin, before filling them in pairs with opposite spins A spin is denoted with an up ↑or down ↓ arrow to fill orbitals This is like trying to find your own room on the same floor before having to share a room with someone else

Electron configuration Practice 10

Question Time What is an electron configuration? What is the Aufbau principle? What is the Pauli Exclusion Principle? What is Hund’s Rule?

Writing Electron Configurations Aufbau diagram for sodium (Na) which has 11 electrons Na electron configuration1s22s22p63s1

Exceptions to Electron Configurations Copper and chromium are exceptions to the Aufbau principle. Element Should be Actually is Copper 1s22s22p63s23p63d44s2 1s22s22p63s23p63d54s1 Chromium 1s22s22p63s23p63d94s2 1s22s22p63s23p63d104s1 B. Some configurations violate the Aufbau Principle because half-filled sublevels are not as stable as filled sublevels, but they are more stable than other configurations

Valence electrons Valence electrons are electrons in the outermost orbital For A group elements the group number corresponds to number of valence electrons. Electron-dot structures – Element’s symbol surrounded by dots representing the valence electrons 8A

Lewis Dot Structure Practice 15

Question Time What two elements are exceptions to the Aufbau rule for electron configurations? What are valence electrons?