Midterm WEDNESDAYCh 8-10.5

Final Exam will be the last day of class. Sorry.

Lewis Structures of Simple Molecules

C

H

H H

H

Cl

O

O O

K+

KClO3

CF4

..

..H C O H

H

H

H

H

C

Ethyl Alcohol (Ethanol)

Potassium Chlorate Carbon Tetrafluoride

......

..

..

..

.. ...... ..

.... C

F

FF

F

......

..

.. ..

..

....

CH4

Methane

Lewis Structures of Simple Molecules Resonance Structures -III Nitrate

N

O

O O

N

O

O O

..

..

..

..

..

..

....

.... ..

.... ..

....

.... ..

N

O

O O......

.. ..

Resonance: Delocalized Electron-Pair Bonding - I

Ozone : O3 ......

..

O O

O ..

........ ..OOO ....

I II

O

O

O

..

........

Resonance Hybrid Structure

One pair of electron’s resonances between the two locations!!

Resonance:Delocalized Electron-Pair Bonding - II

C

CC

CC

C

CC

C

C C

C

C

CC

CC

C

H

HHH

H H

H

H

H

H

H

H

H

HHH

H

HResonance Structure Benzene

Postulating the Hybrid Orbitals in a Molecule

Problem: Describe how mixing of atomic orbitals on the central atoms leads to the hybrid orbitals in the following:

a) Methyl amine, CH3NH2 b) Xenon tetrafluoride, XeF4

Plan: From the Lewis structure and molecular shape, we know the number and arrangement of electron groups around the central atoms,from which we postulate the type of hybrid orbitals involved. Then we write the partial orbital diagram for each central atom before and after the orbitals are hybridized.

Postulating the Hybrid Orbitals in a Molecule

Problem: Describe how mixing of atomic orbitals on the central atoms leads to the hybrid orbitals in the following: a) Methyl amine, CH3NH2 b) Xenon tetrafluoride, XeF4

Plan: From the Lewis structure and molecular shape, we know the number and arrangement of electron groups around the central atoms,from which we postulate the type of hybrid orbitals involved. Then we write the partial orbital diagram for each central atom before and after the orbitals are hybridized.Solution:a) For CH3NH2: The shape is tetrahedral around the C and N atoms.Therefore, each central atom is sp3 hybridized. The carbon atom has four half-filled sp3 orbitals:

Isolated Carbon Atom2s 2p sp3

Hybridized Carbon Atom

The N atom has three half-filled sp3 orbitals and one filled with a

lone pair.

2s 2p sp3

C

H

H

H

H

H

N

..

b) The Xenon atom has filled 5 s and 5 p orbitals with the 5 d orbitals empty.

5 s 5 p 5 d

Hybridized Xe atom:

5 d

Isolated Xe atom

sp3d2

b) continued:For XeF4. for Xenon, normally it has a full octet of electrons,which would mean an octahedral geometry, so to make the compound, two pairs must be broken up, and bonds made to the four fluorine atoms. If the two lone pairs are on the equatorial positions, they will be at 900 to each other, whereas if the two polar positions are chosen, the two electron groups will be 1800 from each other. Thereby minimizing the repulsion between the two electron groups.

Xe

F

F

F

F..

..

Xe

F

F F

F

Square planar

1800

Fig. 9.14

Figure 9.15: Electronegatives of the elements.

Fig. 9.16

Fig. 9.17

Determining Bond Polarity from Electronegativity Values

Problem: (a)Indicate the polarity of the following bonds with a polarity arrow: O - H, O - Cl, C - N, P - N, N - S, C - Br, As - S (b) rank those bonds in order of increasing polarity.Plan: (a) We use Fig. 9.16 to find the EN values, and point the arrow toward the negative end. (b) Use the EN values.Solution: a) the EN of O = 3.5 and of H = 2.1: O - H

the EN of O = 3.5 and of Cl = 3.0: O - Cl the EN of C = 2.5 and of P = 2.1: C - P the EN of P = 2.1 and of N = 3.0: P - N the EN of N = 3.0 and of S = 2.1: N - S the EN of C = 2.5 and of Br = 2.8: C - Br the EN of As = 2.0 and of O = 3.5: As - O b) C - Br < C - P < O - Cl < P - N < N - S < O - H < As - O

0.3 < 0.4 < 0.5 < 0.9 < 0.9 < 1.4 < 1.5

Fig. 9.18

Percent Ionic Character as a Function ofElectronegativity Difference (En)

Fig. 9.19

Lewis Structures for Octet Rule Exceptions

Cl

F

F

F ....

..

..

....

..

.... ..

..

..

..

BCl

Cl

Cl......

..

......

Each fluorine atom has 8 electrons associated. Chlorine has 10 electrons!

Each chlorine atom has8 electrons associated. Boron has only 6!

Cl ClBe....

..

.. ....

Each chlorine atom has8 electrons associated. The beryllium has only 4 electrons.

NO O

... .... ..

..NO2 is an odd electron atom.The nitrogen has 7 electrons.

Resonance Structures - Expanded Valence Shells..

.. S

F

F

F

FF

F......

.. ......

.. .. .. ....

.. .. ....

Sulfur hexafluoride

....

.. PF

F

F

FF......

......

..

...... ..

..

Phosphorous pentafluoride

O

S

O

O OH H

..

....

.... ..

.. ......

O

S

O

O OH H.. .... ..

........

Sulfuric acid

S = 12e- p = 10e-

S = 12e-

Resonance Structures

Lewis Structures of Simple Molecules

Resonance Structures-VSO O

O

O

SO O

O

O

. .

. . . .

. .. .

. .. .. .

. .

. .

. .

. .

. .

-2

. .

. .

. .. .. .

-2 Sulfate

S

O

O

O Oxx

x = Sulfur electrons o = Oxygen electrons

o o

o o

o o

o o

o o

x o

x x

x o

o o

o o

o o

o o

o *

o *-2

o o

Plus 4 othersfor a total of 6

. .

. .

Chemical Compounds and Bonds

Chemical Bonds - The electrostatic forces that hold the atoms of elements together in the compound.

Ionic Compounds - Electrons are transferred from one atom to another to form Ionic Cpds.

Covalent Compounds - Electrons are shared between atoms of different elements to form Covalent Cpds.

“Cations” - Metal atoms lose electrons to form “ + ” ions.

“Anions” - Nonmetal atoms gain electrons to form “ - ” ions.

Mono-atomic ions form binary ionic compounds

Figure 2.16: Molecular and structural formulas and molecular models for some compounds.

Ethanol

• An ionic compound is composed of cations and anions.

• Ions are arranged in a repeating three-dimensional pattern, forming a crystal.

• The formula of an ionic compound gives the smallest possible integer number of ions in the substance (without writing charges) so that the combination is electrically neutral.

• The formula gives the formula unit of the compounds. A formula unit is not a molecule!

Fig. 2.18

Figure 2.19: A model of a portion of NaCl.

He

Ne

Ar

Kr

Xe

Rn

The Periodic Table of the Elements

Most Probable Oxidation State

Cr Mn Fe Co Ni

Mo

W

Tc

Re

Ru

Os

Rh

Ir

Pd

Pt

+1

+2

+3 +4

+3 +_4 - 3 - 2 - 1

0

H

Li

Na

K

Rb

Cs

Fr

Sc

Y

Be

Mg

Ca

Sr

Ba

Ra

La

Ac

B

Al

Ga

In

Tl

Ti

Rf

Hf

Zr

C

Si

Ge

Sn

Pb

F

Cl

Br

I

At

O

S

Se

Te

Po

N

P

As

Sb

Bi

Zn

Cd

Hg

+ 2+1

Cu

Ag

Au

+5

V

Nb

Ta

Ce

Th

Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

+3

+3

Du Sg Bo Ha Me

Fig. 2.20

Fig. 2.19

• What is formula of the ionic compound of Mg2+ and N3-?

• The common multiple of the charges is 6, so we need three Mg2+ and two N3-. The resulting formula is

• Mg3N2

• What is the formula of the ionic compound of Ca2+ and PO4

3-?

• The common multiple of the charges is 6, so we need three Ca2+ and two PO4

3-. The resulting formula is

• Ca3(PO4)2

• Chemical nomenclature is the systematic naming of chemical compounds.

• Compounds that are not organic are called inorganic compounds.

Carbon monoxide, carbon dioxide, carbonates, and cyanides are also classified as inorganic compounds.

• Naming Inorganic Compounds

1.Name the cation.2.Name the anion.

• 2. Some main-group metals with high atomic number have more than one cation. One cation will have the charge of the group number minus 2; the second cation will have a charge equal to the group number

Pb in Group IVA(14) has two ions:Pb2+ and Pb4+

Tl in Group IIIA(13) has two ions:Tl+ and Tl3+

• 3. Most transition metals form more than one cation, of which one is +2.Zn and Cd form only the +2 ion.Ag forms only the +1 ion.

• 4. Nonmetal main-group elements form one monatomic anion with a charge equal to the group number minus 8.F in Group VIIA(17) forms the F- ion.S in Group VIA(16) forms the S2- ion.N in Group VA(15) forms the N3- ion.

• Naming Monatomic Ions

• Monatomic cations are named after the element if the element forms only one cation.

• If more than one cation forms:a.In the Stock system, the charge is written using a

Roman numeral and is enclosed in parentheses.Cu2+ is copper(II).Cu+ is copper(I).

• Fe3+ is iron(III)• Fe2+ is iron(II)

• Hg2+ is mercury(II).• The second ion mercury forms is diatomic: Hg2

2+ is mercury(I).

• Cr3+ is chromium(III).• Cr2+ is chromium(II).

• Mn2+ is manganese(II).• Co2+ is cobalt(II).

• Zinc forms only Zn2+, so it is called zinc ion.• Cadmium forms only Cd2+, so it is called cadmium

ion.• Silver forms only Ag+, so it is called silver ion.

• Polyatomic Ion

• An ion consisting of two or more atoms chemically bonded together and carrying an electrical charge.

• Table 2.5 lists common polyatomic ions.

• Cations

• mercury(I) or mercurous Hg22+

• ammonium NH4+

• Anions

• peroxide O2-

• hydroxide OH-

• cyanide CN-

• What are the names of the following ionic compounds?– BaO– Cr2(SO4)3

BaO is barium oxide.Cr2(SO4)3 is chromium(III) sulfate or chromic sulfate.

• What are the chemical formulas for the following ionic compounds?– potassium carbonate– manganese(II) sulfate

The ions K+ and CO32- form K2CO3

The ions Mn2+ and SO42- form MnSO4

• Binary Molecular Compounds

• A compound composed of only two elements.

• Binary compound of a metal and a nonmetal are generally named using ionic rules.

• Naming Binary MolecularMolecular Compounds

• We usually name the elements in the order given in the formula.

• Name the first element using the element name.

• Name the second element using the element root + -ide suffix.

• Add a prefix to each name to indicate the number of atoms of that element. The prefix mono- is used only when needed to distinguish two compounds of the same two elements.

• The final vowel of the prefix is often dropped when followed by an element name that begins with a vowel. Oxygen is the most common example.N2O4 dinitrogen tetroxide (“a” is dropped)

NO nitrogen monoxide (only one “o”)(also called nitric oxide)

Don’t use thesewhen naming ioniccompounds--they’reONLY for covalentcompounds!!

• Some compounds have common names that differ from their systematic names:

H2S hydrogen sulfide (the “di” is omitted)

H2O water

NH3 ammonia

• Common names need to be memorized.

• What are the names of the following compounds?– OF2

– S4N4

– BCl3

OF2 is oxygen difluoride

S4N4 is tetrasulfur tetranitride

BCl3 is boron trichloride

• What are the formulas for the following binary molecular compounds?– carbon disulfide– nitrogen tribromide– dinitrogen tetrafluoride

The formula for carbon disulfide is CS2.

The formula for dinitrogen tetrafluoride is N2F4.

The formula for nitrogen tribromide is NBr3.

• Acids and Corresponding Anions

• Oxoacids contain hydrogen, oxygen, and a third central atom.

To name an acid from its anion name:1. Change an –ate suffix to –ic.2. Change an –ite suffix to –ous.3. Add the word “acid.””

• For example:HNO3 nitric acidH2SO4 sulfuric acid

Figure 2.23: Molecular model of nitric acid.

What is the formula for nitric acid?

HNO3

• Bromine has an oxoacid, HBrO2, bromous acid

(compare to HClO2, chlorous acid). What are the name and formula of the corresponding anion?

The anion corresponding to HBrO2 isbromite, BrO2

-.

• Hydrate

• A compound that contains water molecules weakly bound in the crystals.

• The formula of a hydrate is written with a dot before the water molecule(s) included.

• For example:CuSO45H2O

• Hydrates are named using the anhydrous (without water) compound name followed by the prefix for the number of water molecules included and the word “hydrate.”

• For example:CuSO45H2O is named

copper(II) sulfate pentahydrate.

• A compound whose common name is green vitriol has the chemical formula FeSO47H2O. What is the chemical name of this compound?

FeSO47H2O is iron(II) sulfate heptahydrate.

• Calcium chloride hexahydrate is used to melt snow on roads. What is the chemical formula of the compound?

The chemical formula for calcium chloride hexahydrate is CaCl26H2O.

• Organic Compounds

• An important class of molecular substances; they contain carbon combined with other elements – notably hydrogen, oxygen, and nitrogen.

• Hydrocarbons contain only carbon and hydrogen.

• A functional group is a reactive portion of a molecule that undergoes predictable reactions.

•Examples•Name of Group

•Functional Group

•Methyl alcohol•AlcoholOH

•Dimethyl ether•EtherO

•Acetic acid•Carboxylic acid

C

O

OH

• A chemical equation is the symbolic representation of a chemical reaction in terms of chemical formulas.

• For example: 2Na + Cl2 2NaCl

• Reactants are the starting materials; they are written on the left of the equation.

• Products are the materials at the end of the reaction; they are written on the right of the equation.

• Because a reaction must accurately describe the chemical reaction, it must be consistent with the law of conservation of mass.

• When this is not the case, after correct formulas are written for each reactant and product, the coefficients are adjusted so that the same number of each atom is present in both the reactants and the products.

• This is called balancing the equation.

• For example, the reaction of sodium with chlorine produced sodium chloride.

• First, we determine the correct formula for each compound.

Sodium is Na.Chlorine is Cl2.

Sodium chloride is NaCl.

Second, we write the reaction.Na + Cl2 NaCl

• Third, we check the number of each atom on each side of the equation.

• This equation shows two Cl atoms on the reactant side and only one Cl atom on the product side. To balance the Cl atoms, we insert a coefficient of “2” before NaCl on the product side.

Na + Cl2 2NaCl

Na + Cl2 2NaCl

• Now the Na are not balanced: there is one on the reactant side and there are two on the product side. To balance Na, we insert the coefficient “2” before Na on the reactant side.

2Na + Cl2 2NaCl

• The reaction is now balanced!

• Balance the following equation:

• CS2 + O2 CO2 + SO2

Tally the number of each atom on each side:C 1 on reactant side; 1 on product sideS 2 on reactant side; 1 on product sideO 2 on reactant side; 4 on product side

Begin by inserting the coefficient “2” before SO2 on the product side. We leave O2 until later because it is an element.

• CS2 + O2 CO2 + 2SO2

• Tally the atoms again:

• C 1 on reactant side; 1 on product side

• S 2 on reactant side; 2 on product side

• O 2 on reactant side; 6 on product side

• Insert a “3” before O2:

• CS2 + 3O2 CO2 + 2SO2

• CS2 + 3O2 CO2 + 2SO2

• Tally the atoms again:

• C 1 on reactant side; 1 on product side

• S 2 on reactant side; 2 on product side

• O 6 on reactant side; 6 on product side

• The reaction is now balanced!

• Balance the following equation:

• NH3 + O2 NO + H2O

Tally the number of each atom on each side:N 1 on reactant side; 1 on product sideH 3 on reactant side; 2 on product sideO 2 on reactant side; 2 on product side

Begin by inserting the coefficient “2” before NH3 on the reactant side and the coefficient “3” before H2O on the product side. We leave O2 until later because it is an element.

• 2NH3 + O2 NO + 3H2O

• Tally the atoms again:

• N 2 on reactant side; 1 on product side

• H 6 on reactant side; 6 on product side

• O 2 on reactant side; 4 on product side

• To balance N, insert a “2” before NO:

• 2NH3 + O2 2NO + 3H2O

•2NH3 + O2 2NO + 3H2O

•Tally the atoms again:N 2 on reactant side; 2 on product side

H 6 on reactant side; 6 on product side

O 2 on reactant side; 5 on product side

•Since this gives us an odd number oxygens, we double the coefficients on NH3, NO, and H2O and to balance O, insert a “5” before O2.

Tally the atoms again to double check:

4NH3 + 5O2 4NO + 6H2O

N 4 on reactant side; 4 on product side

H 12 on reactant side; 12 on product side

O 10 on reactant side; 10 on product side

•The reaction is now balanced!

• Balance the following equation:

• C2H5OH + O2 CO2 + H2O

Tally the number of each atom on each side:C 2 on reactant side; 1 on product sideH 6 on reactant side; 2 on product sideO 3 on reactant side; 3 on product side

Begin by balancing H. Insert the coefficient “3” before H2O on the product side. We leave O2 until later because it is an element.

• C2H5OH + O2 CO2 + 3H2O

• Tally the number of each atom on each side:

• C 2 on reactant side; 1 on product side

• H 6 on reactant side; 6 on product side

• O 3 on reactant side; 5 on product side

• To balance C, insert a “2” before CO2.