More bondingQuick Overview of:

Ionic BondingMetallic 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 O2- ion and not an O3- 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?

QuickTime™ and aGIF decompressor

are needed to see this picture.

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

Intermolecular ForcesThese are forces between two molecules that determine how they react and interact together

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

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

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

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 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 F2

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 H2O

• H has 1 valence e-

• O has 6 valence e-

• 1 + 1 + 6 = 8 valence e- in H20

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:

• CCl4

• PH3

Lewis structures for molecules with multiple bonds

• Example - CO2

• Count valence e-: Carbon has 4, Oxygen has 6

• 4 + 2(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- (16 - 4 = 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

Lewis Structure

• Hydrogen Fluoride

• 1 + 7 = 8 valence e-

• H - F

• Distribute remaining 6 valence e-

• 3 lone pairs on F

Lewis structures• N2

• Diatomic Nitrogen Molecule

• 5 + 5 = 10 valence e-

• N - N

• Distribute remaining 8 valence e-

lewis Structures

• NH3

• Ammonia

• 5 + 3(1) = 8 valence e-

• H - N - H | H

• Distribute remaining 2 e-

lewis Structures• CH4

• Methane

• 4 + 4(1) = 8 valence e-

H |

• H - C - H | H

• No remaining e- to distribute

lewis Structures• SO3

• Sulfur trioxide

• 6 + 3(6) = 24 valence e-

• O - S - O | O

• 24 - 6 = 18 remaining e- to distribute

• No ONE way to do it = resonance structure!

Question

• Write lewis structures for following molecules:

• HF

• N2

• NH3

• CH4

• SO3