More bonding Quick Overview of: Ionic Bonding Metallic bonding Hydrogen bonding Quick Overview of: Ionic Bonding Metallic bonding Hydrogen bonding

OBJECTIVES - BONDING LEARN ABOUT STABLE ELECTRON CONFIGURATIONS UNDERSTAND FACTORS GOVERNING IONIC SIZE UNDERSTAND ELECTRON SEA MODEL EXPLAIN DIPOLE-DIPOLE ATTRACTION AND HYDROGEN BONDING REVIEW LONDON DISPERSION FORCES

STABLE ELECTRON CONFIGURATIONS IN STABLE COMPOUNDS, ATOMS TEND TO ACHIEVE THE ELECTRON CONFIGURATION OF THE NEAREST NOBLE GAS

ionic compounds Non-Metals gain e- obtain configuration of next noble gas Metals lose e- obtain configuration of previous noble gas

Ionic Compounds Ions group together to form electrically neutral compounds

Ionic size When a metal loses e -, cation is smaller than neutral atom

Ionic size When a nonmetal gains e -, anion is larger than neutral atom

questions How can we predict that oxygen will form an O 2- ion and not an O 3- ion? Predict the formula for an ionic compound formed from the following elements: Mg, S K, Cl Cs, F Ba, Br Why are cations smaller than their parent atoms ? Why are anions larger?

Metallic bonding Metals are ATOMIC SOLIDs that form crystals (network of atoms) What holds atoms together? “Electron Sea” model - atoms in sea of valence electrons Electrons shared amongst all atoms

dipole -dipole attraction The attractive force between the positively charged end of one polar molecule and the negatively charged end of another molecule

HYDROGEN BONDING Strong dipole-dipole attraction Occurs between molecules in which H is bound to very electronegative atom such as F, O, and N Strong attraction due to polarity and due to small size of H atom (allows close approach by positive dipole)

London dispersion forces weak forces resulting from temporarily uneven distribution of e- induces a dipole in a neighbor between atoms and non-polar molecules

Lewis structures

Objectives - Lewis structures To Learn to Write Lewis Structures Using Knowledge of Electron Configurations To Learn to Write Lewis Structures for Molecules with Multiple Bonds

What is a lewis structure? Representation of molecule or polyatomic ion showing how valence e - arranged among atoms Only show valence e - since these are ones participating in bonding e - shown as dots

Lewis structure - ionic compound No dots shown around Na, since it gives up its 1 valence e - Cl shown with 8 valence e -, since it gains 1 e - Charges on ions shown outside of brackets

Lewis structures - covalent bonds Hydrogen wants duet (2) of e - H · · H H : H

Lewis structures - covalent bonds Fluorine wants octet (8) of e - Shares pair of e - with another Fluorine atom to make F 2

Lewis structures - terminology Electron pair between two atoms = bonding pair Electron pairs not between two atoms = unshared pairs or lone pairs Each fluorine has 1 shared pair and 3 lone pairs

Tips for writing lewis structures Include all valence e - from all atoms Total # of e - = sum of all valence e - from atoms in molecule Bonded atoms share 1 or more e - pairs Arrange e - so each atom surrounded by enough e - to fill valence orbitals (usually octet; duet for Hydrogen)

Lewis structure steps Find sum of valence e - of all atoms in molecule example H 2 O H has 1 valence e - O has 6 valence e = 8 valence e- in H 2 0

Lewis structure steps Use one pair e - for bond between each pair of bound atoms. A line can can be used to represent a pair of e - H - O - H

Lewis structure steps Arrange remaining e - to satisfy duet rule for H and octet rule for other atoms Note: two lone pairs on oxygen atom

Questions Write Lewis structures for each of the following molecules: CCl 4 PH 3

Lewis structures for molecules with multiple bonds Example - CO 2 Count valence e - : Carbon has 4, Oxygen has (6) = 16 valence e - Show bonds between C and the Oxygens: O - C - O

Lewis structures for molecules with multiple bonds O - C - O Distribute remaining e- ( = 12 e-) to achieve noble gas config Put two pairs between C and each O so C has noble gas configuration

Single bonds, double bonds, Triple bonds Single bond: 1 pair e - shared by atoms Double bond: 2 pair e - shared by atoms Triple bond: 3 pair e - shared by atoms

Resonance structures A condition occurring when more than one VALID Lewis structure can be written for a molecule Shows limitations of bonding models we have developed

Question Write lewis structures for following molecules: HF N 2 NH 3 CH 4 SO 3

Lewis Structure Hydrogen Fluoride = 8 valence e- H - F Distribute remaining 6 valence e- 3 lone pairs on F

Lewis structures N 2 Diatomic Nitrogen Molecule = 10 valence e - N - N Distribute remaining 8 valence e -

lewis Structures NH 3 Ammonia 5 + 3(1) = 8 valence e - H - N - H | H Distribute remaining 2 e -

lewis Structures CH 4 Methane 4 + 4(1) = 8 valence e - H | H - C - H | H No remaining e - to distribute

lewis Structures SO 3 Sulfur trioxide 6 + 3(6) = 24 valence e - O - S - O | O = 18 remaining e - to distribute No ONE way to do it = resonance structure!