Do Now:What are the three types of bonds?Compare them. Which compounds contain which bonds?Why?

Metallic Bond

•Properties of metals? High electrical and thermal conductivity, luster (shiny), malleable, ductile

Valence electrons are delocalized. The bond results from the electrostatic attraction between the delocalized electrons and the metallic ions.

Positive ions (cations) in a "sea"

of delocalized electrons.

Ionic Bond

•Transfer of electrons•Metals lose elelctron(s) to form positive ions (cations)

•Nonmetals gain electron(s) to form negative ions (anions)

Li. :Cl:

:

. Li+ :Cl:

:

..-

Lower IE More negative EA

Ionic Compounds

•Properties???Brittle, crystalline substances with high melting points, most soluble in water, conduct electricity when melted and in solution,

Lattice Energy

Molecular Compounds - Covalent Bonding

• Gas, Liquid,Solid with generally low melting points, brittle, do not conduct electricity• Looking at hydrogen molecule, H2

• High electron density between nuclei. The atoms are held together because the two positive nuclei are attracted to the concentration of negative charge between them. The shared

pair in a covalent bond acts as “glue”

Lewis Structures

• Use Lewis Dot Diagrams• Lone pairs (nonbonding pairs – unshared)

• Bonding Pairs –shared between two nuclei

Draw Lewis structures for N2, O2, and F2•Compare bond length and bond enthalpy, enthalpy change H to break bond

•Estimate H for synthesis of ammonia

Energy Calculations•Estimate Hf

o for potassium chloride provided with:

•Lattice energy of KCl: -690 kJ/mol•First IE for K: 419 kJ/mol•Electron affinity of Cl: -349 kJ/mol•Bond Energy of Cl2: 239 kJ/mol•Enthalpy of sublimation for K: 64 kJ/mol

Ionic and Covalent Bond are on the extremes, what about HCl•Polar covalent bond

•Dipole moment – measure of is the measure of net molecular polarity, tell us about the charge separation in a molecule.

Electronegativity – ability of atom to attract electrons. Explain trend

•H and O•S and S•Li and Cl

-

What type of bond exists between…

Lewis Structures

•Type of structural formula that uses dots or dashes to indicate bonds

Bromine molecule, Br2

Water, H2O

Ethyne, C2H2

Methane, CH4

DO NOW

•Draw the Lewis Structure for NCl3 and HCN

•Indicate the shared and unshared pairs of electrons

•What is another term for shared electrons?

alencehelllectronairepulsion

VSEPR

This theory states that pairs of valence electrons are arranged as far apart from each

other as possible

Draw Lewis Structures for

• H2, C2H2, BH3, NH3, H2O, PCl5, SF6

• In the last two examples, will you satisfy the octet rule? Explain

Example Shape Angle

H2 and C2H2 Linear 180º

BH3 Trigonal Planar 120º

Methane Tetrahedral~109.5º

Ammonia Trigonal Pyramidal ~107º

Water Bent (V-shaped) ~104.5º

Phosphorus Pentachloride

Trigonal Bipyramidal

90º, 120º

Sulfur hexafluoride

Octaheral 90º

?

A molecule’s attractive forces impacts its melting and boiling points as well as many other properties.

•Will a molecule that is highly attracted to another molecule of its kind have a high boiling point or a low boiling point? In which state will the substance typically be found at room tempterature?

Polarity of Molecule•Polar Molecule (Dipoles) – have a positive end and a negative end

•Nonpolar Molecule - has an equal distribution of electrons and therefore no positive or negative ends

First let’s review: Distinguish between polar and nonpolar bonds. What do those terms mean and how do you make this determination?

Polar or Nonpolar Molecules…

•H2

•CO2

•H2O

Shape of molecule and polarity of bonds determines polarity of molecule.

Valence Bond Theory

• Covalent bonds form when a pair of electrons is shared by overlapping atomic orbitals on adjacent atoms.

Consider HF, draw the valence electron configuration for H and F

2p __ __ __H 1s__ F 2s__

X XX

Methane, CH4

•Draw the valence electron configuration for C and H

Carbon’s four sp3 hybrid orbitals

Add four hydrogen s orbitals

Boron Trihydride, BH3

•Draw the valence electron configuration for B

Boron’s three sp2 hybrid orbitals, has 1 empty p orbital

Add three hydrogen s

orbitals

Ethyne, C2H2

•Draw the valence electron configuration for C

Add two hydrogen s

orbitals

Each carbon has two sp orbitals and two p orbitals

• Sigma () bond – results from end to end overlap of atomic orbitals• Pi ()bond – side be side overlap of atomic orbitals

Which bonds are

Try C2H4

Summary of Valence Bond Theory

Hybridization VSEPR theory shape Example

sp Linear (2) C2H2

sp2 Trigonal planar ( 3) BH3

sp3 Tetrahedral, bent(2 shared, 2 unshared), pyramidal (4)

CH4

Trigonal bipyramidal (5) PCl5Octahedral (6) SF6

sp3d

sp3d2