2. Covalent bond bonds in which electrons are shared resulting in a molecule

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1 REVIEW: UNIT 3: BONDING: OXIDATION NUMBERS: NAMING CHEMICALS What are valence electrons? How do you determine valence electrons? How do you write dot notations? The outermost electrons are always s and p electrons. Electrons participate in reactions-not protons or neutrons. I. CHEMICAL BONDS: Forces that hold atoms together by transferring OR sharing electrons. Creates compounds. A. Types of chemical bonds 1. Ionic bond bonds formed from ions (+ or ) in which electrons are transferred 2. Covalent bond bonds in which electrons are shared resulting in a molecule II. Reason why Elements form Chemical Bonds. A. Octet rule-atoms bond to obtain eight (8) electrons in their outermost energy level. 1. Atoms give up, take or share electrons to get a filled outer shell. B. Chemical formulas-shorthand way to show what a compound is made up of using chemical symbols. 1. Molecule smallest unit of covalently bonded elements. 2. Formula unit-smallest unit of an ionic bond. 3. Subscripts in a formula give the number of atoms of that element in a molecule. 4. Coefficients- number in front of a compound giving the total number of molecules of that compound. 5. EXAMPLES: Fill in the blanks below using the above definitions. COMPOUND ATOMS MOLECULES or FORMULA UNITS a. H 2 SO 4 H S O b. 3 C 6 H 12 O 6 C H O c. 2 Ca 3 (PO 4 ) 2 Ca P O III. IONIC BONDS-electrons are transferred from a metal to a nonmetal A. Characteristics 1. Ions are formed when electrons are either lost (+ion formed) or gained ( ion formed). 2. Ions in ionic compounds are arranged in crystals by attraction of + and charges. Compounds are brittle, have high melting points, and conduct electricity when dissolved in water. 3. The difference in electronegativity values is great because the metal readily gives the electron to a nonmetal that wants to steal it. Example: a group I element bonding with a group VI element or group I with a group VII or group II with group VI or group II with group VII. 1

2 B. Ions formed 1. Cation: + ion (electrons lost-metals) 2. Anion: ion (electrons gained-nonmetals) 3. Polyatomic ions-charged group of covalently bonded atoms. The entire group will bond to another ion according to its charge, + or. (See VII) C. In an ionic compound: positive charges must = the negative charges 1. # of electrons gained = # of electrons lost IV. COVALENT BOND Electrons are shared between 2 nonmetals. Form molecules A. NONPOLAR COVALENT BONDS - electrons between elements are always shared equally. A bond in which there is an equal attraction for the shared electrons, resulting in a balanced distribution of charge. No dipoles. 1. hydrogen, H 2 ; nitrogen, N 2 ; oxygen, O 2 ; fluorine, F 2 ; chlorine, Cl 2 ; bromine, Br 2 ; iodine, I 2 Note: these are the only elements that bond to themselves it does not refer to the bonding these elements do when forming compounds. HOFBrINCl acronym for remembering the 7 diatomics. 2. C-H bond is typically nonpolar covalent as well. 3. Electronegativity difference is the same or nearly the same as in C-H. B. ELECTRONEGATIVITY: ability of the nucleus of one element to attract electrons of another element to obtain an octet (become stable). 1. Electronegativity generally increases from left to right within a period. As the elements increase in atomic number, and get closer to having eight (8) electrons, the atom has a stronger attraction for electrons. 2. Electronegativity generally decreases from top to bottom within a group. Electrons are moving further away from the nucleus and there is not as strong of an attraction for the electrons (atoms get bigger). 3. The most electronegative element is Fluorine. 4. Metals have a small attraction for valence electrons (low electronegativity). Francium has the lowest. 5. Nonmetals have a high attraction for valence electrons (high electronegativity). 6. Noble gases have zero electronegativity. 2

3 C. POLAR COVALENT BONDS bonds are shared unequally creating dipoles. 1. Polar Bond-A covalent bond in which there is an unequal attraction for the shared electrons and a resulting unbalanced distribution of charge. a. Partial charges are created resulting in positive and negative sides (dipole). Think of south and north poles on magnets. b. EX: water the oxygen has a and the hydrogen has a + c. Determining the polarity- these polar bonds are formed typically from 2 nonmetals that are close to each other on the periodic table. Note: You will be expected to recognize trends and not be dependent on actual values. d. The larger the difference between the electronegativities of two nonmetals, the more polar the bond will be. D. Characteristics of Molecular (Covalent) Compounds 1. Covalent bonds are much weaker than ionic bonds 2. Lower boiling point because less energy is needed to break the bond apart. 3. Poor conductors of electricity because there are no charged particles V. OXIDATION NUMBERS-the real or apparent charge an atom or ion has when all bonds are assumed to be ionic (how many electrons would an atom want to lose or gain to have 8 electrons?). A. A charged atom 1. A charge indicates whether the atom gained electrons ( ) or lost electrons (+). 2. The number on that charge indicates how many electrons were gained or lost. B. Rules to know: The oxidation number (charge) of examples 1. any atom in its free state is zero (0). Ca (s), F 2(g), Hg (l) 2. any simple ion is the charge on that ion. Na +1, Ca +2, F, O 3. a polyatomic ion is equal to the sum of the SO 3 individual oxidation numbers. 4. All oxidation numbers are assigned so that the sum of the oxidation numbers equals the net (entire) charge on the molecule or polyatomic ion. 5. For a neutral molecule the sum of the charges equals zero this is true of all compounds. 3

4 6. EX: find the oxidation number of each atom in the following: a. H 2 S b. Na 2 O c. KBr H S Na O K Br d. CaCl 2 e. Al 2 S 3 f. CuI Ca Cl Al S Cu I g. FeF 3 h. Ag 3 N i. NiO Fe F Ag N Ni O j. H 3 PO 4 k. HCN HSO 4 H P O H C N H S O m. Cr 2 O 7 2 Cr O n. HClO 4 H Cl O VI. LEARNING TO NAME CHEMICALS. A. You MUST know the names of the following polyatomic ions (formulas next chapter!) ammonium NH 4 2. nitrate NO 3 3. acetate C 2 H 3 O 2 4. nitrite NO 2 5. carbonate CO 3 6. permanganate MnO 4 7. bicarbonate HCO phosphate PO 4 9. chlorate ClO sulfate SO chromate CrO sulfite SO dichromate Cr 2 O bisulfate HSO hydroxide OH 16. cyanide CN 17. perchlorate ClO iodate IO oxalate C 2 O hypochlorite ClO 21. bromate BrO chlorite ClO mercury (I) Hg 2 4

5 B. Special elements with two oxidation numbers 1. Iron Fe +2 iron (II) Fe +3 iron (III) 2. Copper Cu +1 copper (I) Cu +2 copper (II) 3. Tin Sn +2 tin (II) Sn +4 tin (IV) 4. Mercury Hg +2 2 mercury (I) Hg +2 mercury (II) VII. WRITING NAMES FROM CHEMICAL FORMULAS A. Binary compounds (2 elements only) composed of metal (cation) and nonmetal (anion) 1. Name metal first using full element name. 2. Look up oxidation number for metal on the periodic table. a. If the metal is a transition element or an element with more than one oxidation number listed, figure out the charge, use parenthesis ( ) with roman numerals after the name of the metal. b. If the metal has ONLY ONE oxidation number do NOT use ( ). 3. Name the nonmetal second, drop the ending and add ide to the end. 4. EX: NaCl Sodium -change chlorine to chloride = sodium chloride a. CaO b. KBr c. Na 2 S d. CuCl 2 e. AgI f. ZnCl 2 g. Fe 2 O 3 h. PbCl 4 i. MgBr 2 B. Binary compound composed of two nonmetals (no ions). 1. The least electronegative element is named first using the full element name. a. The first element has no prefix unless it contains more than one atom. b. Prefixes: 1=mono; 2=di; 3=tri; 4 tetra; 5=penta; 6=hexa; 7=hepta; 8=octa 2. The most electronegative element is named second and ALWAYS has a prefix. a. Drop the ending and add ide b. Drop the final o or a of a prefix if the element starts with a vowel 5

6 3. EX: As 2 O 5 2 atoms of arsenic-need prefix di; 5 atoms of oxygen-prefix pent a. As 2 O 5 diarsenic pentoxide b. N 2 O 3 c. NO d. N 2 O 5 e. CO f. CCl 4 g. SbCl 3 h. P 2 S 3 C. Compounds containing polyatomic ions (more than two elements) 1. Metals are named first using the full element name 2. Polyatomic ions retains its name whether a positive ion or negative ion. 3. EX: NaOH sodium and hydroxide = sodium hydroxide a. NH 4 Cl b. Pb 3 (PO 4 ) 2 c. NaC 2 H 3 O 2 d. FeCrO 4 e. Fe 2 (CrO 4 ) 3 f. Cu 2 SO 4 g. CuSO 4 h. Fe(ClO 3 ) 3 i. CuClO 3 6

7 THREE MAJOR TYPES OF BONDS IONIC BONDS POLAR COVALENT BOND NONPOLAR COVALENT BOND 1. The electronegativity 1. The electronegativity 1. The electronegativity difference between the difference between the difference adds up to atoms is great. atoms is slight. zero 2. In general, any group I 2. In general, any two different 2. In general, any two or group II with a group nonmetals bonded together identical elements VI or group VII element. bonded together. 3. When dissolved in water, 3. When dissolved in water, 3. These do not separate in crystals separate into + these do not separate into ions water. In fact, they repel & ions that conduct but have a + and ends like water since nonpolar electricity. poles of a magnet. bonds do not have a + or end. 4. Examples: 4. Examples: 4. Examples: NaCl, KI, BaO, CaBr 2, H 2 O, N 2 O 5, P 2 O 5, BrI, H 2, O 2, F 2, Br 2, I 2, N 2, Cl 2, and usually any group I As 2 O 5, C 6 H 12 O 6, C 12 H 22 O 11 C 4 H 10, C 5 H 12, C 6 H 14, or group II metal with C 7 H 16 polyatomic ions like KNO 3 or Na 2 SO 4 7

8 Naming Compounds First determine which of the following identities fits your compound, then follow the rules. 1. Metal w/ one ox. # and a nonmetal Name metal using full element name Name nonmetal second o Drop the ending and add ide EX: CaCl 2 Calcium chloride 2. Metal w/ more than one ox. # and a nonmetal Name metal using full element name Determine oxidation number Use roman numerals in ( ) to identify ox. # Name nonmetal second o Drop the ending and add ide EX: FeO Iron(II)oxide; Fe 2 O 3 Iron(III)oxide 3. Two nonmetals-do not contain ions Name first nonmetal using full element name o use prefix if there is 2 or more atoms Name second nonmetal as if an ion o always use prefix mono (1), di (2), tri (3), tetra (4), penta (5), hexa (6), hepta (7), octa (8) EX: CO Carbon monoxide 4. Metal and a polyatomic ion Name metal using full element name Name polyatomic ion second EX: Mg(NO 3 ) 2 Magnesium nitrate 5. Metal w/ more than one ox. # and a polyatomic ion Name metal using full element name o Determine oxidation number o Use roman numerals in ( ) to identify ox. # Name polyatomic ion second o recognize anion and name EX: PbSO 4 Lead (II) Sulfate 6. Polyatomic ion and a nonmetal Name polyatomic ion first o Recognize cation and name Name nonmetal second o Drop the ending and add ide EX: NH 4 Br Ammonium bromide 7. Two polyatomic ions Recognize cation and name first Recognize anion and name second EX: NH 4 OH Ammonium hydroxide 8

9 Name Date OXIDATION NUMBER ASSIGNMENT UNIT 3 DIRECTIONS: Determine the oxidation numbers for all elements and polyatomic ions in the following compounds. 1. LiCl Li = Cl = 2. ZnI 2 Zn = I = 3. Mg 3 N 2 Mg = N = 4. KF K = F = 5. CuO Cu = O = 6. PbI 2 Pb = I = 7. Cu 2 O Cu = O = 8. SnS 2 Sn = S = 9. FeBr 3 Fe = Br = 10. CaH 2 Ca = H = 11. H 2 O 2 H = O = 12. NaClO 3 Na = ClO 3 = 13. K 2 SO 4 K = SO 4 = 14. BaCO 3 Ba = CO 3 = 15. AlPO 4 Al = PO 4 = 16. NH 4 NO 3 NH 4 = NO 3 = 17. NiCrO 4 Ni = CrO 4 = 18. KMnO 4 K = MnO 4 = 19. CoCr 2 O 7 Co = Cr 2 O 7 = 20. Li 2 SO 3 Li = SO 3 = 21. AgC 2 H 3 O 2 Ag = C 2 H 3 O 2 = 22. Fe(NO 2 ) 2 Fe = NO 2 = 9

10 Assign oxidation numbers to EACH element in the following substances NH 4 3. C 2 H 3 O CO 3 7. HCO 3 9. ClO 3 N H 2. NO 3 C H O 4. NO 2 C O 6. MnO 4 H C O 8. 3 PO 4 Cl O SO 4 N O N O Mn O P O S O Identify the bonds in the following substances as ionic (I), polar covalent (PC) or nonpolar covalent (NPC). Apply your rules do not use random guess work. 1. CaCl NH 3 2. P 2 O HC 2 H 3 O 2 3. CS LiF 4. HCl 24. KNO 3 5. C 6 H 12 O O 2 6. KBr 26. PbO 7. Cl C 12 H 22 O NaCl 28. I 2 9. C 2 H 5 OH 29. H 2 O 10. Br PbBr SnS N 2 O N CdBr CO 33. CaCO Na 2 SO H 2 O As 2 O H KI 36. MnCl Br Fe(OH) BaO F Na 3 PO NO Fe 2 O (NH 4 ) 2 SO 4 10

11 Determine the names of the following: 1. CO NH 4 NO 2 2. N 2 O Mg 3 (PO 4 ) 2 3. H 2 O Cr(OH) 3 4. CaCO BaCr 2 O 7 5. CO 24. K 2 O 2 6. (NH 4 ) 2 SO NaHCO 3 7. NO CuCl 2 8. BaO CaS 9. Na 3 PO Hg 2 Cl MnCl PbBr H 2 SO As 2 O K 2 Cr 2 O PbO 13. SnS KH 14. NaHSO SnS 15. CdBr AgCN 16. Fe 2 O Ca(MnO 4 ) Fe(OH) AuCl HgCl CI Ni 3 (PO 4 ) YP From the following compounds determine the number of atoms and molecules. Compound atoms molecules 1. 2 Ni 3 (PO 4 ) 2 _ Ni _ P O 2. AuCl 3 _ Au _ Cl 3. 4(NH 4 ) 2 SO 4 _ N H _ S O 4. NaHSO 4 _ Na _ H _ S _ O 11