Electron Configurations

Objectives Apply Pauli exclusion principle, the aufbau principle, and Hund’s rule to write electron configurations using orbital diagrams and electron configuration notation Define valence electrons and draw electron-dot structures representing an atom’s valence electrons

Electron Configuration The arrangement of electrons in an atom Atom wants to be in its most stable state…this is the ground state…its lowest energy state You will be able to write Ground state electron configurations Excited state electron configurations

Aufbau principle States that each electron occupies the lowest energy orbital available. Fill orbitals from lowest energy to highest energy P. 135 Some features of the principle All orbitals related to an energy sublevel are of equal energy In a multi-electron atom, the energy sublevels within a principle energy level have different energies In order of increasing energy, the sequence of energy sublevels within a principle energy level is s, p, d, f Orbitals related to energy sublevels within one principle energy level can overlap orbitals related to energy sublevels within another principle level

Pauli Exclusion Principle States that a maximum of two electrons may occupy a single atomic orbital, but only if the electrons have opposite spins. We use up and down arrows to represent forward and backward electron spin (like spinning tops in two different directions)

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 orbitals

Orbital Filling Sequence

Max # of Electrons in each orbital P = 6 D = 10 F = 14

Writing the Configurations I shall show you now!!! Lots of practice now!!!

Exceptions to Predicted Configurations Because atoms want to be as stable as possible, their orbitals have to be either half-filled or fully-filled Cr family Cu family

Abbreviated Configurations The lazy-man’s way

Valence Electrons Valence electrons are electrons in the atom’s outermost orbitals – generally, those orbitals associated with the atom’s highest principle energy level Can be no more than 8 electrons in element’s valence shell Valence electrons are the electrons responsible for forming chemical bonds

Lewis Dot Structure Model of element and its valence electrons Element symbol surrounded by up to 8 dots Fill in 1 dot on each side at a time and then pair up the dots

Homework 5.3 Assessment P.146 #57-64 Write out electron configurations for Elements with atomic # 1-34