13 December 2011

13 December 2011

Objective: You will be able to: describe the three types of bonding

and determine which type of bonding is present in a compound

Do now: On the first slide of your handout, brainstorm everything you know about bonding.

Homework: p. 400 #5, 6, 16, 17, 20, 21 due tomorrow, will be checked

Agenda

I. Do nowII. Ionic vs. Covalent vs. Metallic

Bonding Notes, Videos and Demo

Chemical Bonding

What do you know about bonding?

chemical bond: a strong force of attraction that holds two atoms together. Involves only the valence electrons.

Types of Bonds

ionic: attractive force between ions of opposite charges, often a metal cation and a non-metal anion.

covalent: results from sharing electrons between two atoms, usually non-metal atoms.

http://www.youtube.com/watch?v=QqjcCvzWwww http://www.youtube.com/watch?v=yjge1WdCFPs metallic: occurs when the nuclei of a

collection of metal atoms simultaneously attract their collective electrons.

http://www.drkstreet.com/resources/metallic-bonding-animation.swf

Ionic or Covalent?

Why? Which have both ionic and covalent bonds?

a. KBrb. SO2

c. H2SO4

d. CH3COOHe. Na3PO4

f. CaCO3

Lewis symbol

valance electrons as dots Draw the Lewis symbol of the first

18 elements. left, right, top, bottom, top, bottom

left, right

octet rule: representative elements tend to gain, lose, or share electrons until they are surrounded by eight valence electrons (an octet)

This gives atoms noble gas configuration with full s and p sublevels

Noble gas configurations are very stable. Hydrogen requires only two electrons to

attain noble gas configuration

14 December 2011

Objective: You will be able to: describe ionic and covalent bonding and

draw Lewis structures for covalent compounds.

Homework Quiz: Week of Dec. 12a. Draw dot diagrams for sodium and sulfur. b. Using arrows, show what happens to their

valence electrons when they bond. c. Write the name of the compound formed.

Agenda

Homework Quiz Homework answers Isoelectronic ions Ionic bonding and lattice energy Covalent Bonding Lewis StructuresHomework: p. 401 #30, 35, 39, 41, 44

Isoelectronic

having the same electron configuration as a noble gas When an element attains a noble gas

configuration, does it turn into a noble gas? Why or why not?

Which are isoelectronic with one another? N3-, K+, Ca2+, O2-, F-, Ne, Br-, Kr, Sc3+,

Na+, Al3+, Se2-, Mg2+

Ionic Bonding

Ions form when electrons transfer from an atom of low ionization energy (usually a metal) to an atom of high electron affinity (usually a non-metal).

The electrostatic attraction between two oppositely charged ions = ionic bond

Crystal lattice demo http://www.mhhe.com/physsci/chemistry

/animations/chang_7e_esp/bom1s2_11.swf

lattice: a stable, ordered, solid, 3D array of ions.

lattice energy, ∆Hlattice, is the energy required to completely separate a mole of solid ionic compound into its gaseous ions.

KF(s) → K+(g) + F-(g) ∆Hlattice = +808 kJ/mol

Example Lattice Energies

Compound Lattice Energy (kJ/mol)

LiF 1030LiCl 834LiI 730NaF 910NaCl 788NaBr 732NaI 682

Ions of Transition Metals

Remember that the d orbital fills before s

When a transition metal is ionized, it loses the s electrons before the d electrons

Fe [Ar] 3d6 4s2

Fe2+ [Ar] 3d6

Fe3+ [Ar] 3d5

Write the electron configuration for Cr3+ and Sn4+

Covalent Bonding

formed between two atoms that share one or more pairs of electrons

Lewis structures show shared pairs of electrons (bonding pairs)

carbon dioxide:

Lewis Structures

Rules1. Total the valance electrons of all the bonded

atoms2. Use one pair of electrons to bond each outer

atom to the central atom (usually the atom in least abundance)

3. Complete the octets around the outer atoms4. Place any remaining electrons on the central

atom5. If there are not enough electrons to give the

central atom an octet, make multiple bonds.

NO3-

Practice Problems

Br2

CH4

H2O H2CO SeF2

CF4

CHCl3

CO2

BF3

SO3

NH4+

HCN

Resonance Structures two or more Lewis structures that

are equally good representations of the bonding in a molecule or ion.

Usually differ only in the positions of multiple or single bonds and unpaired electrons

Formal Charge

the number of valence electrons in an isolated atom minus the number of electrons assigned to the atom in the Lewis structure

Used to determine which Lewis structure is the most suitable to represent bonding Choose the one closest to zero.

Steps to Formal Charge

1. Examine each atom one at a time.2. Count both electrons in a lone pair

(nonbonding electrons) and one electron per bond.

3. Compare this number with the group number.

4. If you have one less electron than the group # indicates, the charge is +1

One more electron than the group #, the charge is -1, etc.

Example: Nitrate Ion

Example: Ammonium Ion

Formal Charge Practice Problems

a. ClO3-

b. CHO2-

c. C2H3Cl

19 December 2011

Objective: You will be able to: calculate bond energies and review

chemical bonding Homework Quiz: Draw two resonance

structures for diazomethane, CH2N2. Show formal charges for both structures. The skeletal structure is:H C N NH

Agenda

I. Homework QuizII. Bond strength and enthalpyIII. Problem SetHomework: Problem Set due Weds.

Strengths of Covalent Bonds

∆HBDE = bond dissociation energy (bond enthalpy)

the enthalpy change for the breaking of bonds in one mole of a gaseous substance

Bond breaking ∆H always positive, always endothermic

Bond making is exothermic!

∆Hrxn = sum of the bond enthalpies of the broken bonds – sum of the bond enthalpies of the bonds formed

Multiple bonds are shorter and stronger than single bonds

Example

Use average bond enthalpies to estimate the enthalpy change of the following reaction:

2H2O → 2H2 + O2

Practice Problems

Calculate the enthalpy of reaction for the process:

a. H2(g) + Cl2(g) → 2HCl(g)b. H2(g) + F2(g) → 2HF(g)c. H2(g) + C2H4(g) → C2H6(g)

This week…

Today: Problem Set Work Time Tomorrow: Green crystal lab part 1:

reaction and growing crystals Thurs: Green crystal lab parts 2 and 3:

Washing and drying crystals and problem set work time

Problem set due Tuesday after vacation Vacation Assignment (distributed

tomorrow) due Wednesday after vacation

21 December 2011

Objective: You will be able to: synthesize a green crystal for later

analysis Do now:

Grab a pair of goggles and sit with your lab partner.

Take out the lab packet.

Reaction and reagents

iron (III) chloride hexahydrate with potassium oxalate

iron (III) chloride is a brown solution at the front lab tables pipette 8 mL

potassium oxalate is a white crystal at the side lab tables weigh 12 grams on weighing paper

distilled water is in the wash bottles ice is in the white coolers at the front – you can

put your product beaker directly into the cooler

Work quickly

Your product needs to chill for about 30 minutes before you pour off the solvent and redissolve your crystals!

We’ll store the crystals in a sample bottle tomorrow.

Work on your problem set while you wait.

For now, collect data on your lab handout.

22 December 2011

Objective: You will be able to: separate your crystal from the

solution and dry it

Winter Break Assignment

Liquids and Intermolecular Forces Read pages 461-472 and 489-499 Complete the following problems by

Tuesday, Jan. 3: page 504 #1, 2, 5, 6, 7, 10, 12, 14,

16, 18, 21, 22, 24, 25, 59, 60, 62, 66, 70, 72, 73, 79, 81, 85, 91, 94

Today

Watch demo of vacuum filtration. Complete Day 2 and Day 3 of

experiment Work on problem set in pairs

work efficiently and quietly stay in your seat unless you need

to move around for the lab