more bonding quick overview of: ionic bonding metallic bonding hydrogen bonding quick overview of:...
TRANSCRIPT
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?
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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