CHEM 120: Introduction to Inorganic Chemistry

Instructor: Upali Siriwardane (Ph.D., Ohio State University)

CTH 311, Tele: 257-4941, e-mail: upali@chem.latech.edu

Office hours: 10:00 to 12:00 Tu & Th ; 8:00-9:00 and 11:00-12:00 M,W,& F

Chapters Covered and Test dates

Tests will be given in regular class periods from 9:30-10:45 a.m. on the following days:

September 22,     2004 (Test 1): Chapters 1 & 2

October 6,           2004(Test 2): Chapters 3, & 4

October 20,         2004 (Test 3): Chapter 5 & 6

November 3,        2004 (Test 4): Chapter 7 & 8

November 15,      2004 (Test 5): Chapter 9 & 10

November 17,      2004 MAKE-UP: Comprehensive test (Covers all chapters

Grading:

[( Test 1 + Test 2 + Test3 + Test4 + Test5)] x.70 + [ Homework + quiz average] x 0.30 = Final Average

                                            5

Chapter 4: Structure and properties of ionic and covalent compounds

We now put atoms and ions together to form compounds

Chapter 4. Structure and Properties of Ionic and Covalent Compounds

1. Classify compounds as ionic, covalent, or polar covalent bonds.

2. Write the formulas of compounds when provided with the name of the compound.

3. Name common inorganic compounds using standard conventions and recognize the common names of frequently used substances.

4. Predict the differences in physical state, melting and boiling points, solid-state structure, and solution chemistry that result from differences in bonding.

5. Draw Lewis structures for covalent compounds and polyatomic ions.

6. Describe the relationship between stability and bond energy.

7. Predict the geometry of molecules and ions using the octet rule and Lewis structure.

8. Understand the role that molecular geometry plays in determining the solubility and melting and boiling points of compounds.

9. Use the principles of VSEPR theory and molecular geometry to predict relative melting points, boiling points, and solubilities of compounds.

Start learning the formulas and the names and charges of the ions found in table

"Why have we been so..."

Why have we been so interested in where the electrons are in an atom? And what is the importance of valence electrons?

Valence e’s are involved in_______--the no of valence e’s has an important influence on ______ of bonds formed. The filled inner core does not directly affect bond formation.

Compound

Bonds are formed by a transfer of ________ from one atom to another or by a ______ _________ between 2 atoms.

Lewis (dot) Symbols

Slide 9

Lewis symbols for A groups

The elements’ symbol represents the inner core of electrons. Put a dot for each valence electron around the symbol.

Remember that the no. of valence electrons for the A groups is equal to ?

Each unpaired electron may be used in bond formation

Remember the octet rule from chapter 3

So the ions formed by the elements in:

IA

IIA

IIIA

VA

VIA

VIIIA

Slide 12

Ionic bonding

Extra stability has been noted for the noble gas configuration (8 e-s in valence shell)--(for A elements)

Ionic bonding

Each atom in the ionic bond

"Ionic compounds are formed between"

Ionic compounds are formed between

And

When forming an ionic bond each atom in the bond attains a noble gas configuration by a “complete” transfer of

"An ionic bond is the..."

An ionic bond is the electrostatic force that holds ions together in an ionic compound

An ionic bond is a very strong bond; ionic cmpds have high m and b pts.

Typical ionic reactions with Lewis structures

What about Li and S?

What about Ca and O

Formula is

What about Ca and N?

Formula is

Covalent bonding

Not all bonds are ionic.

________ bonds are bonds in which two (or more) electrons are ______ by two atoms.

One shared electron pair is

Slide 21

"A reminder:"

A reminder:

Only valence electrons are involved in bonding. Group No. = # valence e-s for A elements.

Covalent bonds are formed

Each atom in bond attains noble gas configuration by sharing of e- pairs (H₂ bond only has 2 e-’s)

Covalent bond formation

Look at formation of H₂ molecule.

H^. + ^.H ----> H:H (H-H)

1s¹ 1s¹ bond formed by overlap of 1s orbitals

What about F₂ or Cl₂?

Slide 25

Polar covalent bonding and electronegativity

Not all covalent bonds are formed btn the same 2 atoms (as H₂, homonuclear diatomic: _______sharing of e-’s in bond)

Polar covalent bonds

What about the bond in H-F?

It is known that F is more likely to attract e-’s to itself than H, leading to an unequal sharing of the e- pair.

The covalent bond in which there is unequal sharing:

Slide 28

Slide 29

Electronegativity

Electronegativity:

.

Eneg is a relative concept. Elements with

Slide 31

Electronegativity differences

0.2 - 0.5 will be a ________________ bond

0.5 - 1.6 will be a ________________ bond

> 1.6 will be a ________________ bond

Electronegativity differences

In general the _______ the difference in eneg btn the 2 atoms in the bond, the ____ ______ the bond.

If the difference is zero, bond (equal sharing of electron pair(s) (H₂, Cl₂, O₂, F₂, N₂)

"If the difference is >"

If the difference is >0 and <1.9, have a : HCl (3.0 - 2.1); HF (4.0-2.1); OH (3.5-2.1)

If the difference is > 1.9, have NaCl (3.0-0.9); CaO (3.5-1.0)

Classify as ionic or covalent

NaCl

CO

ICl

H₂

"Which bond is the most..."

Which bond is the most polar (most ionic), which the least polar (most covalent)?

Li-F Be-F B-F C-F N-F O-F F-F

Slide 37

Chemical formulas

Express composition of molecules (smallest unit of covalent cmpds) and ionic compounds in chemical symbols

H₂O, NaCl

Writing formulas for ionic cmpds

Compounds are neutral overall. Therefore

NaCl is array of Na⁺ and Cl^- ions

Na₂S is array of Na⁺ and S^2- ions

Predict the formulas for the cmpd formed btn

Potassium and chlorine

Magnesium and bromine

Magnesium and nitrogen

Slide 41

Slide 42

Slide 43

Slide 44

Polyatomic ions Table

Just have to memorize

NH₄⁺ ammonium ion

CO₃^2- carbonate ion

CN^- cyanide ion

HCO₃^- hydrogen (or bi) carbonate ion

OH^- hydroxide

Slide 46

"These polyatomic ions also form..."

These polyatomic ions also form ionic cmpds when they are reacted with a metal or a nonmetal in the case of the ammonium ion (or with each other as ammonium sulfate). These polyatomic species act as a

"So the formula for the..."

So the formula for the cmpd formed btn the ammonium ion and sulfur would be:

and between calcium and the phosphate ion:

"Ionic cmpds do not exist..."

Ionic cmpds do not exist in discrete pairs of ions. Instead, in the solid state, they exist as a three dimensional array--crystal lattice --of cations and anions--are neutral overall,

Given name, write formula

potassium oxide

magnesium acetate

Naming ionic cmpds

Name the cation and anion but drop the word ion from both. This includes the polyatomic ions.

Na₂S

Ca₃N₂

Name

Na₃PO₄

NH₄Cl

K₂S

Cations with more than one charge

Cu⁺ copper(I); Cu²⁺ copper(II)

So Cu₂O is and

CuO is

Given name, write formula

Ammonium chloride

potassium cyanide

silver oxide

Magnesium chloride

Sodium sulfate

Iron(II) chloride

To name covalent cmpds

Name the parts as for ionic cmpds (CO: carbon and oxide) but tell how many of each kind of atom by use of Greek prefixies. (Table 4.4)

The mono- (for 1) may be omitted for the first element

"Prefix"

Prefix         meaning

Mono-           1

Di-                 2

Tri-                3

Tetra-            4

Penta-            5

Hexa-            6

Hepta-           7

Octa-              8

Nona-             9

Deca-            10

"CO"

CO

CO₂

P₄S₁₀

Boron trichloride

Water H₂O Ammonia NH₃

Write formula

Diboron trichloride

Sulfur trioxide

Potassium sulfide

Covalent cmpds

Remember covalent cmpds--

A _________ is the smallest unit of a covalent cmpd that retains the characteristics of the cmpd. Molecule - two or more atoms in a definite arrangement held together by chemical bonds. (H₂O, Cl₂) [Cl₂ is considered a molecule but not a cmpd]

Molecular cmpds exist as

Comparison of properties of ionic and covalent cmpds

Physical state:

Ionic cmpds are

Molecular cmpds can be

Comparison continued

Melting (___________) and boiling (_________) pts

In general the melting and boiling temps are much _______for ionic cmpds than for molecular (covalent) cmpds. The ionic bond is very strong and requires a lot of (heat) energy to break the bond. The bond btn molecular species is not as strong.

Comparison continued

Structure in solid state:

Ionic solids--

Covalent solids--

Comparison continued

In aqueous (H₂O) solution:

Ionic cmpds dissociate into the

Many covalent cmpds when dissolved in water retain their structure and molecular identity

"Learn the names,"

Learn the names, formulas, charges, etc for those ions highlighted in table 4.3.

HCO₃^-: you should learn as bicarbonate

Writing Lewis structures for covalent species

These rules are for covalently bonded cmpds only (btn 2 or more nonmetals)

Do not use them for ionic cmpds.

1. Count the total no. of valence electrons (the group no. is equal to the no. of valence electrons).

if the species is an anion, increase the no. of valence electrons by the charge on the ion

"if the species is a..."

if the species is a cation, subtract the charge of the cation from the total no. of valence electrons.

2.Count the total no. of atoms, excluding H, in the molecule or ion. Multiply that no. by 8.

Exception: multiply the no. of H’s by 2.

This tells you how many electrons you would need if you were putting 8 electrons around all atoms without any sharing of electrons (and 2 around all H’s).

"3."

3. Subtract the no. of e-’s calculated in step 1 from the no. in step 2. This gives you the no. of e-’s that must be shared to get an octet around all atoms in the molecule.

4. no. of e-’s that must be shared /2 gives you the no. of bonds.

5. subtract the no. of e-’s that are shared (from step 3) from the total no. of valence e-’s. This gives you the no. of unshared e-’s.

If you divide the no. of unshared e-’s by 2 you get the no. of lone pairs.

"Write the skeletal structure and..."

Write the skeletal structure and fill in with the info you came up with. After you’ve put in the # bonds calculated, fill in the octets.

H (and F) form only one bond. Therefore they can only be terminal atoms in a structure.

So you can not have

C---H---C

It has to be H---C--C

"Examples"

Examples

CH₄

PCl₃

SO₃^2-

NO₃^-

CN^-

COBr₂(C is bonded to O and Br atoms)

SO₂

H₃O⁺(hydronium ion

N₃^-

Slide 70

Multiple bonds

In general a triple bond (N₂) is ________ than a double bond (O₂) which is ________than a single bond (F₂).

Bond order: BO of 1--single bond, BO of 2-- -double bond, BO of 3 --triple bond.

The stronger the bond,

Slide 72

Resonance

Resonance structure –1 of 2 or more Lewis structures for a molecule (ion) that can’t be represented with a single structure

Resonance – use of

Slide 74

"Each resonance structure contributes to..."

Each resonance structure contributes to the actual structure

no single structure is a complete description

positions of atoms must be the same in each, only electrons are moved around

actual structure is an “average”

"Draw resonance structures for SO₃..."

Draw resonance structures for SO₃ and N₃^-.

Exceptions to Octet Rule

There are three classes of exceptions to the octet rule.

1) Molecules with an odd number of electrons;

2) Molecules in which one atom has less than an octet;

3) Molecules in which one atom has more than an octet.

Let’s do Lewis structures for

CO₂ (CS₂)

O₃(SO₂)

I₃^-

3D structure of species

Electrostatic forces in ionic bonds is _____________. But species with covalent bonds have electron pairs concentrated btn 2 atoms and is ..

We use VESPR theory to predict the shape of the covalently bound species.

VSEPR theory

VSEPR

Most stable geometry is one in which electron pairs (electron clouds) are as

Shapes of molecules (3D)

The geometry is determined by the atoms present in the species. See atoms that are bonded to other atoms. Don’t “see” lone pairs but they influence geometry

I. Diatomics (2 atoms only): always ________

H₂, HCl, CO X----X

"II."

II. Polyatomic (3 or more atoms) species: Use VSEPR model to predict shapes

Steps in applying VSEPR

1. Do Lewis structure

2. Count total e- pairs (clouds) around central atom (A). Multiple bonds count as one electron pair (cloud). In reality multiple bonds are bigger than single bonds (electron clouds larger).

"3."

3. Separate e- pairs into bonded pairs (B) and lone pairs (E)

4. Apply table that I give you.

5. Remember that lone pairs of e-’s are invisible, but their presence affects the final molecular geometry!!!!!

Lone e- pair-lone e-pairs are more repulsive than bonded pair-lone pair repulsions or bonded pair-bonded pair repulsions.

VSEPR: valence shell electron pair repulsion

2 electron clouds around a central atom (A)

Slide 87

Slide 88

Slide 89

Slide 90

Table 4.5 (changed)

# e # bonded #lone pairs geom angle clouds pairs pairs

2

3

3

4

4

4

Predict geometry

H₂S

SO₂

CO₂

CF₄

H₂CO

ClO₃^-

ClO₂^-

Polar vs nonpolar cmpds

A molecule is polar if its centers of positive and negative charges do not coincide. If a molecule is polar we say that it acts as a dipole. In an electric field nonpolar molecules (positive and negative centers coincide) do not align with the field but polar molecules do.

Next we will see why this happens and the implications.

Slide 94

Polar molecules

I. Diatomics, A-B

a.If A = B have homonuclear diatomic; has

b. A ≠ B have heteronuclear diatomic

"II."

II. Polyatomic species are more complicated.

Let’s look at VSEPR cases considered.

General rule (my rule):

Which of these are polar?

H₂S

SO₂

CO₂

CF₄

AlCl₃

CHCl₃

SCl₂

Properties based on electronic structure and molecular geometry

Intramolecular forces: within a molecule--bonds

Intermolecular forces: between molecules--these determine important properties as melting and boiling points and solubility

Solubility

Like dissolves like:

Polar cmpds dissolve in polar solvents as ionic and polar cmpds (HCl) in water

Nonpolar cmpds dissolve in nonpolar solvents: oils in CCl₄

Melting and boiling points

Stronger the intermolecular forces the higher the melting and boiling points

In general for cmpds of similar weight: polar moleculaes have stonger forces than nonpolar cmpds

In general for similar structure the greater the mass the stronger the forces

Which have higher melting (boiling pts)

CO and NO

F₂ and Br₂

CH₃CH₂OH and CH₃CH₃


	Instructor: Upali Siriwardane (Ph.D., Ohio State University)
	CTH 311, Tele: 257-4941, e-mail: upali@chem.latech.edu
	Office hours: 10:00 to 12:00 Tu & Th ; 8:00-9:00 and 11:00-12:00 M,W,& F


	Tests will be given in regular class periods from 9:30-10:45 a.m. on the following days:
	September 22, 2004 (Test 1): Chapters 1 & 2
	October 6, 2004(Test 2): Chapters 3, & 4
	October 20, 2004 (Test 3): Chapter 5 & 6
	November 3, 2004 (Test 4): Chapter 7 & 8
	November 15, 2004 (Test 5): Chapter 9 & 10
	November 17, 2004 MAKE-UP: Comprehensive test (Covers all chapters
	Grading:
	[( Test 1 + Test 2 + Test3 + Test4 + Test5)] x.70 + [ Homework + quiz average] x 0.30 = Final Average
	5


	1. Classify compounds as ionic, covalent, or polar covalent bonds.
	2. Write the formulas of compounds when provided with the name of the compound.
	3. Name common inorganic compounds using standard conventions and recognize the common names of frequently used substances.
	4. Predict the differences in physical state, melting and boiling points, solid-state structure, and solution chemistry that result from differences in bonding.
	5. Draw Lewis structures for covalent compounds and polyatomic ions.
	6. Describe the relationship between stability and bond energy.
	7. Predict the geometry of molecules and ions using the octet rule and Lewis structure.
	8. Understand the role that molecular geometry plays in determining the solubility and melting and boiling points of compounds.
	9. Use the principles of VSEPR theory and molecular geometry to predict relative melting points, boiling points, and solubilities of compounds.


	Why have we been so interested in where the electrons are in an atom? And what is the importance of valence electrons?

	Valence e’s are involved in_______--the no of valence e’s has an important influence on ______ of bonds formed. The filled inner core does not directly affect bond formation.


	Bonds are formed by a transfer of ________ from one atom to another or by a ______ _________ between 2 atoms.


	The elements’ symbol represents the inner core of electrons. Put a dot for each valence electron around the symbol.
	Remember that the no. of valence electrons for the A groups is equal to ?

	Each unpaired electron may be used in bond formation


	Extra stability has been noted for the noble gas configuration (8 e-s in valence shell)--(for A elements)

	Ionic bonding

	Each atom in the ionic bond


	Ionic compounds are formed between

	And


	When forming an ionic bond each atom in the bond attains a noble gas configuration by a “complete” transfer of


	An ionic bond is the electrostatic force that holds ions together in an ionic compound


	An ionic bond is a very strong bond; ionic cmpds have high m and b pts.


	Not all bonds are ionic.

	________ bonds are bonds in which two (or more) electrons are ______ by two atoms.

	One shared electron pair is


	A reminder:
	Only valence electrons are involved in bonding. Group No. = # valence e-s for A elements.

	Covalent bonds are formed

	Each atom in bond attains noble gas configuration by sharing of e- pairs (H₂ bond only has 2 e-’s)


	Look at formation of H₂ molecule.

	H^. + ^.H ----> H:H (H-H)
	1s¹ 1s¹ bond formed by overlap of 1s orbitals



	Not all covalent bonds are formed btn the same 2 atoms (as H₂, homonuclear diatomic: _______sharing of e-’s in bond)


	What about the bond in H-F?
	It is known that F is more likely to attract e-’s to itself than H, leading to an unequal sharing of the e- pair.

	The covalent bond in which there is unequal sharing:


	Electronegativity:

	.

	Eneg is a relative concept. Elements with


	0.2 - 0.5 will be a ________________ bond
	0.5 - 1.6 will be a ________________ bond
	> 1.6 will be a ________________ bond


	In general the _______ the difference in eneg btn the 2 atoms in the bond, the ____ ______ the bond.
	If the difference is zero, bond (equal sharing of electron pair(s) (H₂, Cl₂, O₂, F₂, N₂)


	If the difference is >0 and <1.9, have a : HCl (3.0 - 2.1); HF (4.0-2.1); OH (3.5-2.1)

	If the difference is > 1.9, have NaCl (3.0-0.9); CaO (3.5-1.0)


	Which bond is the most polar (most ionic), which the least polar (most covalent)?

	Li-F Be-F B-F C-F N-F O-F F-F


	Express composition of molecules (smallest unit of covalent cmpds) and ionic compounds in chemical symbols
		H₂O, NaCl


	Compounds are neutral overall. Therefore




		NaCl is array of Na⁺ and Cl^- ions
		Na₂S is array of Na⁺ and S^2- ions


	Potassium and chlorine

	Magnesium and bromine

	Magnesium and nitrogen


	Just have to memorize
	NH₄⁺ ammonium ion
	CO₃^2- carbonate ion
	CN^- cyanide ion
	HCO₃^- hydrogen (or bi) carbonate ion
	OH^- hydroxide


	These polyatomic ions also form ionic cmpds when they are reacted with a metal or a nonmetal in the case of the ammonium ion (or with each other as ammonium sulfate). These polyatomic species act as a


	So the formula for the cmpd formed btn the ammonium ion and sulfur would be:




	and between calcium and the phosphate ion:


	Ionic cmpds do not exist in discrete pairs of ions. Instead, in the solid state, they exist as a three dimensional array--crystal lattice --of cations and anions--are neutral overall,


	Name the cation and anion but drop the word ion from both. This includes the polyatomic ions.
	Na₂S

	Ca₃N₂


	Ammonium chloride
	potassium cyanide
	silver oxide
	Magnesium chloride
	Sodium sulfate
	Iron(II) chloride


	Name the parts as for ionic cmpds (CO: carbon and oxide) but tell how many of each kind of atom by use of Greek prefixies. (Table 4.4)
	The mono- (for 1) may be omitted for the first element


	Prefix meaning
	Mono- 1
	Di- 2
	Tri- 3
	Tetra- 4
	Penta- 5
	Hexa- 6
	Hepta- 7
	Octa- 8
	Nona- 9
	Deca- 10