1	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
2	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
3	Chapter 4: Structure and properties of ionic and covalent compounds We now put atoms and ions together to form compounds
4	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.
5	Start learning the formulas and the names and charges of the ions found in table
6	"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.
7	Compound Bonds are formed by a transfer of ________ from one atom to another or by a ______ _________ between 2 atoms.
8	Lewis (dot) Symbols
9
10	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
11	Remember the octet rule from chapter 3 So the ions formed by the elements in: IA IIA IIIA VA VIA VIIIA
12
13	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
14	"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
15	"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.
16	Typical ionic reactions with Lewis structures
17	What about Li and S?
18	What about Ca and O Formula is
19	What about Ca and N? Formula is
20	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
21
22	"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)
23	Covalent bond formation Look at formation of H₂ molecule. H^. + ^.H ----> H:H (H-H) 1s¹ 1s¹ bond formed by overlap of 1s orbitals
24	What about F₂ or Cl₂?
25
26	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)
27	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:
28
29
30	Electronegativity Electronegativity: . Eneg is a relative concept. Elements with
31
32	Electronegativity differences 0.2 - 0.5 will be a ________________ bond 0.5 - 1.6 will be a ________________ bond > 1.6 will be a ________________ bond
33	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)
34	"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)
35	Classify as ionic or covalent NaCl CO ICl H₂
36	"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
37
38	Chemical formulas Express composition of molecules (smallest unit of covalent cmpds) and ionic compounds in chemical symbols H₂O, NaCl
39	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
40	Predict the formulas for the cmpd formed btn Potassium and chlorine Magnesium and bromine Magnesium and nitrogen
41
42
43
44
45	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
46
47	"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
48	"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:
49	"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,
50	Given name, write formula potassium oxide magnesium acetate
51	Naming ionic cmpds Name the cation and anion but drop the word ion from both. This includes the polyatomic ions. Na₂S Ca₃N₂
52	Name Na₃PO₄ NH₄Cl K₂S
53	Cations with more than one charge Cu⁺ copper(I); Cu²⁺ copper(II) So Cu₂O is and CuO is
54	Given name, write formula Ammonium chloride potassium cyanide silver oxide Magnesium chloride Sodium sulfate Iron(II) chloride
55	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
56	"Prefix" Prefix meaning Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8 Nona- 9 Deca- 10
57	"CO" CO CO₂ P₄S₁₀ Boron trichloride Water H₂O Ammonia NH₃
58	Write formula Diboron trichloride Sulfur trioxide Potassium sulfide
59	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
60	Comparison of properties of ionic and covalent cmpds Physical state: Ionic cmpds are Molecular cmpds can be
61	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.
62	Comparison continued Structure in solid state: Ionic solids-- Covalent solids--
63	Comparison continued In aqueous (H₂O) solution: Ionic cmpds dissociate into the Many covalent cmpds when dissolved in water retain their structure and molecular identity
64	"Learn the names," Learn the names, formulas, charges, etc for those ions highlighted in table 4.3. HCO₃^-: you should learn as bicarbonate
65	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
66	"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).
67	"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.
68	"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
69	"Examples" Examples CH₄ PCl₃ SO₃^2- NO₃^- CN^- COBr₂(C is bonded to O and Br atoms) SO₂ H₃O⁺(hydronium ion N₃^-
70
71	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,
72
73	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
74
75	"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”
76	"Draw resonance structures for SO₃..." Draw resonance structures for SO₃ and N₃^-.
77	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.
78	Let’s do Lewis structures for CO₂ (CS₂) O₃(SO₂) I₃^-
79	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.
80	VSEPR theory
81	VSEPR Most stable geometry is one in which electron pairs (electron clouds) are as
82	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
83	"II." II. Polyatomic (3 or more atoms) species: Use VSEPR model to predict shapes
84	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).
85	"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.
86	VSEPR: valence shell electron pair repulsion 2 electron clouds around a central atom (A)
87
88
89
90
91	Table 4.5 (changed) # e # bonded #lone pairs geom angle clouds pairs pairs 2 3 3 4 4 4
92	Predict geometry H₂S SO₂ CO₂ CF₄ H₂CO ClO₃^- ClO₂^-
93	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.
94
95	Polar molecules I. Diatomics, A-B a.If A = B have homonuclear diatomic; has b. A ≠ B have heteronuclear diatomic
96	"II." II. Polyatomic species are more complicated. Let’s look at VSEPR cases considered. General rule (my rule):
97	Which of these are polar? H₂S SO₂ CO₂ CF₄ AlCl₃ CHCl₃ SCl₂
98	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
99	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
100	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
101	Which have higher melting (boiling pts) CO and NO F₂ and Br₂ CH₃CH₂OH and CH₃CH₃