Lewis Structures, Orbital Diagrams, & Electron Configuration Chiquita McDaniel General Chemistry I Laboratory

How to Draw Lewis Structures Two types: Covalent (sharing e-s) & Ionic (transfer e-s) COVALENT Draw the skeletal structure Least electronegative element as the central atom F and H always occur as outer atoms Count the number of valence electrons present Draw bonds in between the outer atoms and the central atom (each bond has two electrons) Complete the octet of the outer atoms (8 e-s) There are three exceptions to this rule (read pages 406-408 in your book) Then complete the octet of the central atom if there are e-s present, if not take e-s from outer atoms to make a double or triple bond

Example CO2 NH3 NH4+

IONIC COMPOUNDS Take each atom and draw the valence e-s surrounding the atom Show how the e-s are transferred from each atom Draw brackets around each individual atom, placing the transferred electrons on the atom Example: K2O , NaCl

Resonance When more than one Lewis structure exists for a compound Caused by delocalized bonding (double bonds) These double bonds can be at either bond at any given time However only one is more plausible than others Determined by calculating formal charges Example O3

Calculating Formal Charges FC= total number of valence e-s – (# of non bonded e- s + 1/2 of the # of bonded electrons) Choosing the correct Resonance structure Sum of all formal charges in a neutral molecule must be zero Sum of all formal charges in an ion must equal to the charge of the ion Small or zero formal charges on individual atoms are better than large ones Negative charges should reside on the most electronegative atom Adjacent negative formal charges should be avoided

Orbital Diagram & Electron Configuration

ELECTRON CONFIGURATION s, p, d, f Types of sublevels, each have a specific number of orbitals S: 1 orbital holds only 2 e-s P: 3 orbitals holds only 6 e-s D: 5 orbitals holds only 10 e-s F: 7 orbitals holds only 14 e-s Orbitals fill in the following order 1s2s2p3s3p4s3d4p5s4d5p6s This is called the ground state configuration using the “Aufbau” principle (build up) The number represent the energy level its on (period) and the letter represents which orbital the electron resides in Can use the periodic table to predict the order of filling without remembering the order above.

ELECTRON CONFIGURATION Nobel gas configuration: is using the electron configuration of Nobel gas preceding the atom as the core and then adding on the remaining electrons.

Orbital diagram N O 1s 2s 2p 1s 2s 2p Expanded version of EC. Shows the orientation of the individual electrons in their orbitals Two Rules to Keep in Mind Pauli Exclusion Rule Orbitals can’t hold more than two electrons No 2 electrons can have the same 4 Quantum Numbers Hund’s Rule Electrons occupy these orbitals singularly first then pair up N O 1s 2s 2p 1s 2s 2p