CHEM 120: Introduction to Inorganic Chemistry. Chapters Covered and Test dates

Transcription

1 CHEM 120: Introduction to Inorganic Chemistry Instructor: Upali Siriwardane (Ph.D., Ohio State University) CTH 311, Tele: , Office hours: 10:00 to 12:00 Tu & Th ; 8:00 9:00 and 11:0012:00 M,W,& F Chapters Covered and Test dates Tests will be given in regular class periods from 9:3010:45 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 MAKEUP: 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, solidstate 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 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.

2 Compound Lewis (dot) Symbols Bonds are formed by a transfer of from one atom to another or by a between 2 atoms. Lewis (dot) symbols Introduced by G. N. Lewis Useful for representative (sp block) elements only Group no. = no of valence e s (no of dots) 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

3 Ionic bonding Extra stability has been noted for the noble gas configuration (8 es 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 Typical ionic reactions with Lewis structures + Na + F Na F An ionic bond is a very strong bond; ionic cmpds have high m and b pts. What about Li and S? What about Ca and O Formula is Li + S 2 Li S

4 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 A reminder: Only valence electrons are involved in bonding. Group No. = # valence es for A elements. Covalent bonds are formed Each atom in bond attains noble gas configuration by sharing of e pairs (H 2 bond only has 2 e s) Covalent bond formation What about F 2 or Cl 2? Look at formation of H 2 molecule. H. +. H > H:H (HH) 1s 1 1s 1 bond formed by overlap of 1s orbitals

5 2 Cl Cl Cl or Cl Cl Lone pairs Bonding pairs Usual representation pairs of valence electrons not involved in covalent bond formation Lewis structure representation of covalent bonding in which lone pairs are shown as pairs of dots and bonding pairs are (usually) shown as lines Polar covalent bonding and electronegativity Not all covalent bonds are formed btn the same 2 atoms (as H 2, homonuclear diatomic: sharing of e s in bond) Polar covalent bonds What about the bond in HF? 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. Polar covalent bond or polar bond is a covalent bond with greater electron density around one of the two atoms electron poor region electron rich region e poor H F H F δ + δ e rich The covalent bond in which there is unequal sharing: Na Continuum of bond polarity Cl (Nearly) complete e transfer = ionic bond Electronegativity: Electronegativity H Cl Unequal sharing of e pair = polar covalent bond.. es are polarized toward Cl Eneg is a relative concept. Elements with Cl Cl Equal sharing of e pair = nonpolar covalent bond

6 Electronegativity differences will be a bond will be a bond > 1.6 will be a bond Lanthanides 1.11,3 Actinides 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) (H 2, Cl 2, O 2, F 2, N 2 ) If the difference is >0 and <1.9, have a : HCl ( ); HF (4.02.1); OH ( ) If the difference is > 1.9, have NaCl (3.00.9); CaO (3.51.0) NaCl CO Classify as ionic or covalent Which bond is the most polar (most ionic), which the least polar (most covalent)? LiF BeF BF CF NF OF FF ICl H 2

7 Classify the following bonds as ionic, polar covalent, or covalent. A) the CC bond in H 3 CCH 3 B) the KI bond in KI C) the NB bond in H 3 NBCl 3 D) the CF bond in CF 4 Chemical formulas Express composition of molecules (smallest unit of covalent cmpds) and ionic compounds in chemical symbols H 2 O, NaCl Writing formulas for ionic cmpds Compounds are neutral overall. Therefore Predict the formulas for the cmpd formed btn Potassium and chlorine Magnesium and bromine NaCl is array of Na + and Cl ions Na 2 S is array of Na + and S 2 ions Magnesium and nitrogen Symbol Name Symbol Name H + Hydrogen ion H Hydride ion Li + Lithium ion F Fluoride ion Na + Sodium ion Cl Chloride ion K + Potassium ion Br Bromide ion Be 2+ Mg 2+ Beryllium ion Magnesium ion I O 2 Iodide ion Oxide ion Ca 2+ calcium ion S 2 Sulfide ion Ba 2+ barium ion N 3 Nitride ion Zn 2+ zinc ion P 3 Phosphide ion

8 Formula Name Formula Name NO 3 nitrate CO 3 2 carbonate Symbol (Stock system) Common Symbol (Stock system) Common NO 2 nitrite SO 4 2 sulfate Cu + copper(i) cuprous Hg 2 2+ mercury(i) mercurous CN cyanide SO 3 2 sulfite Cu 2+ copper(ii) cupric Hg 2+ mercury(ii) mercuric MnO 4 permanganate PO 4 3 phosphate Fe 2+ iron(ii) ferrous Pb 2+ lead(ii) plumbous OH hydroxide PO 3 3 phosphite Fe 3+ iron(iii) ferric Pb 4+ lead(iv) plumbic O 2 2 peroxide ClO 4 perchlorate Sn 2+ tin(ii) stannous Co 2+ cobalt(ii) cobaltous HCO 3 hydrogen carbonate ClO 3 chlorate Sn 4+ tin(iv) stannic Co 3+ cobalt(iii) cobaltic HSO 4 hydrogen sulfate ClO 2 chlorite Cr 2+ chromium(ii) chromous Ni 2+ nickel(ii) nickelous HSO 3 hydrogen sulfite ClO hypochlorite Cr 3+ chromium(iii) chromic Ni 4+ nickel(iv) nickelic HPO 4 2 hydrogen phosphate CrO 4 2 chromate Mn 2+ manganese(ii) manganous Au + gold(i) aurous H 2 PO 4 dihydrogen phosphate C 2 H 3 O 2 acetate Mn 3+ manganese(iii) manganic Au 3+ gold(iii) auric Polyatomic ions Table Just have to memorize NH 4 + ammonium ion CO 3 2 carbonate ion CN cyanide ion HCO 3 hydrogen (or bi) carbonate ion OH hydroxide NO 3 NO 2 PO 3 4 SO 2 4 nitrate ion nitrite ion phosphate ion sulfate ion HSO 4 hydrogen sulfate ion SO 3 2 sulfite ion CH 3 COO (C 2 H 3 O 2 ) acetate ion 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:

9 Given name, write formula Ionic cmpds do not exist in discrete pairs of ions. Instead, in the solid state, they exist as a three dimensional arraycrystal lattice of cations and anionsare neutral overall, potassium oxide magnesium acetate Naming ionic cmpds Name Name the cation and anion but drop the word ion from both. This includes the polyatomic ions. Na 2 S Ca 3 N 2 Na 3 PO 4 NH 4 Cl K 2 S Cations with more than one charge Cu + copper(i); Cu 2+ copper(ii) So Cu 2 O is and CuOis Given name, write formula Ammonium chloride potassium cyanide silver oxide Magnesium chloride Sodium sulfate Iron(II) chloride

10 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 meaning Mono 1 Di 2 Tri 3 Tetra 4 Penta 5 Hexa 6 Hepta 7 Octa 8 Nona 9 Deca 10 CO CO 2 Diboron trichloride Write formula P 4 S 10 Boron trichloride Sulfur trioxide Water H 2 O Ammonia NH 3 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. (H 2 O, Cl 2 ) [Cl 2 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

11 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 (H 2 O) solution: Ionic cmpds dissociate into the Many covalent cmpds when dissolved in water retain their structure and molecular identity Learn the names, formulas, charges, etc for those ions highlighted in table 4.3. HCO 3 : 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 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).

12 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 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 CHC It has to be HCC Examples CH 4 PCl 3 SO 2 3 NO 3 CN COBr 2 (C is bonded to O and Br atoms) SO 2 H 3 O + (hydronium ion N 3 Draw Lewis structure of CO 2 i) Valence electrons: x 6 = 16 ( 8 pairs) ii) Central atom C; O C O iii) Give octet to carbon O C O Try to fill octet to O iv) Count electrons: 4 bond pairs = 4 pairs 4 lone pairs = 4 pairs 8 electron pairs Multiple bonds In general a triple bond (N 2 ) is than a double bond (O 2 ) which is than a single bond (F 2 ). Bond order: BO of 1single bond, BO of 2 double bond, BO of 3 triple bond. The stronger the bond, Terminology used in describing Lewis structures of molecul Bond pairs: An electron pair shared by two atoms in a bond. Lone pair: An electron pair found solely on a single atom. Single covalent bond Bond between two atoms when they shared 1 pair Double covalent bond Bond between two atoms when they shared 2 pairs. Triple covalent bond Bond between two atoms when they shared 3 pairs. Lewis Structure, Stability, Multiple Bonds, and Bond Energies Bond order The stability of a covalent compound is related to the bond energy. The magnitude of the bond energy increases and the bond length decreases in the order: single bond > double bond > triple bond. Bond Energy order: single < double < triple Bond length order: single (1) < double (2) < triple (3)

13 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 Draw resonance structures for SO 3 and N 3. 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 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 CO 2 (CS 2 ) O 3 (SO 2 ) I 3

14 3D structure of species VSEPR theory 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 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 H 2, HCl, CO XX Steps in applying VSEPR II. Polyatomic (3 or more atoms) species: Use VSEPR model to predict shapes 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).

15 3. Separate e pairs into bonded pairs (B) and lone pairs (E) 4. Apply table that I give you. VSEPR: valence shell electron pair repulsion 2 electron clouds around a central atom (A) 5. Remember that lone pairs of e s are invisible, but their presence affects the final molecular geometry!!!!! Lone e pairlone epairs are more repulsive than bonded pairlone pair repulsions or bonded pairbonded pair repulsions. 2 electron clouds Three electron clouds Three electron clouds Four electron clouds

16 Table 4.5 (changed) Predict geometry # e # bonded #lone pairs geom angle clouds pairs pairs H 2 S SO 2 CO 2 CF 4 H 2 CO ClO 3 ClO 2 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. Molecules are subjected to electric field Polar molecules align with field Nonpolar molecules are not affected Polar molecules I. Diatomics, AB a.if A = B have homonuclear diatomic; has II. Polyatomic species are more complicated. Let s look at VSEPR cases considered. General rule (my rule): b. A B have heteronuclear diatomic

17 H 2 S SO 2 CO 2 CF 4 AlCl 3 CHCl 3 Which of these are polar? 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 SCl 2 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 CCl 4 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 F 2 and Br 2 CH 3 CH 2 OH and CH 3 CH 3