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Chemical Nomenclature Mixtures versus Compounds Law of Definite Proportions Chemical Bonds, Ionic & Covalent –Octet rule, valences Names and Formulas –Common.

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Presentation on theme: "Chemical Nomenclature Mixtures versus Compounds Law of Definite Proportions Chemical Bonds, Ionic & Covalent –Octet rule, valences Names and Formulas –Common."— Presentation transcript:

1 Chemical Nomenclature Mixtures versus Compounds Law of Definite Proportions Chemical Bonds, Ionic & Covalent –Octet rule, valences Names and Formulas –Common and Chemical names Ions and Ionic Charge –Cations and Anions –Polyatomic Anions

2 Mixtures Mixtures are physical (NOT chemical) combinations –Many mixtures have NO chemical reaction potential Sugar or Salt dissolved in water Solder, a mixture of Tin and Lead Unlimited number of potential combinations –Some mixtures have chemical reaction potential Rocket Propellants (e.g. zinc + sulfur) –Mixture of oxidizer and combustible material Gunpowder (Charcoal + Sulfur + Potassium Nitrate) –Stable for hundreds of years until ignited Thermite (iron oxide + aluminum powder) –Reacts yielding liquid iron to weld railroad track Hydrogen and Oxygen, gasoline and air –Requires an initiator (e.g. heat from spark or flame) –Other mixtures are inherently unstable Metallic Sodium and water react violently Liquid rocket propellants burn when mixed Acids and Bases neutralize each other

3 Compounds Inorganic compounds, “entangled elements” –Chemical reaction creates bonding + heat energy Constituents are no longer mechanically separable Creation of a new material unlike the constituents –Gaseous hydrogen and oxygen burn to form liquid water –Metallic sodium and chlorine gas combine to form table salt Law of Definite Proportions –Atoms usually combine in small integer multiples –Inorganic common ratios are 1 to 5 NaCl, CaCl 2, Al 2 O 3, H 2 SO 4, PCl 5

4 Molecules, Ions, Chemical Bonds Ionic Bonds –Complete charge separation Electrons relocated from donor to acceptor atoms Unlike atoms involved (e.g. Sodium Chloride) –Opposite sides of periodic table Dissolve in water to form charged ions –Ionic crystals formed when no solvent Electrostatic “binding energy” holds crystal together –No distinct partnering All Na and Cl ions are equivalent in solution or solid crystal Neutral charge balance, but joined pairs of ions

5 Molecules, Ions, Chemical Bonds Ionic Bonds –“Cation” is positively charged ion Attracted to “Cathode” which is negative pole Typically a metal with 1-3 missing electrons –Na 1 +, Ca 2+, Fe 3+ –“Anion” is negatively charged ion Attracted to “Anode” which is a positive pole Typically a halogen or oxide with 1-2 extra electrons –F 1-, Br 1-, O 2- … Polyatomic Anions also very common –These are very stable molecular species –NO 3 1-, SO 4 2-, PO 4 3-

6 NaCl dissolving in water Each ion “solvated” by water molecules, attracted to oppositely charged ends of water molecules Equal numbers of Na + & Cl - ions in solution

7 Molecules, Ions, Chemical Bonds Covalent Bond –Shared electrons between atoms Pair of electrons involved, one from each atom –Same kind of atoms often linked to each other Carbon-carbon electron sharing very common Diatomic elements: O 2, H 2, N 2, F 2 … not He, Ne, Xe –“Octet Rule” describes stable configurations Total of 8 electrons around atom most stable –Exception is Hydrogen = 2 for complete “s” shell Can achieve an octet via sharing –My one + your one = two to share –Carbon is ideal candidate for sharing »4 electrons to share with 4 other elements

8 Special Arrangements 7 elements have Diatomic Molecules –They travel in pairs, mainly halogens H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 Groups or arrays are also common –Sulfur as chains of S 8 –Carbon has multitude of structures Diamond crystals, Graphite layers, amorphous charcoal New carbon materials include Nanotubes, “buckeyball” spheres, graphene sheets

9 Molecules, Ions, Chemical Bonds Why not diatomic He, Ne, Ar, Kr … ? –These already have a full octet No need to share for 8 outer shell electrons –Full outer shell means INERT No chemical reactions if no electrons to transfer –NO compounds form with He, Ne, etc. Can ionize (remove electrons) with high voltage –Electrons fall back with emission of light –Low pressure Neon (pink) used in signs –Argon (blue) used in high power lasers –Xenon (white) for camera’s electronic flash

10 Non-Metal Compounds Many combinations involve Oxygen –CO 2, NO 2, SO 2, etc. Naming conventions –Non-oxygen element named first If multiple atoms, use multiplier wording Di, tri, tetra, penta, … (mono usually not used) –Oxygen next, with multiplier wording Mono, di, tri, tetra, …. –A few examples Carbon dioxide = CO 2 Carbon Monoxide = CO Dinitrogen pentoxide = N 2 O 5

11 Nomenclature of multiple additions Mono (one to add, “monogamous”, “monopole”) –Carbon Monoxide, is CO (C≡O) Di (two to add, think “dipole”, “diode”) –Carbon Dioxide, is CO 2 (O=C=O) Tri (three to add, “trimester”, “triangle”, “tritium”) –Nitrogen Tri-Iodide, is NI 3 Tetra (4 to add, think “tetrahedron”) –Carbon Tetrachloride, is CCl 4 Penta (5 to add, think “pentagon”, “pentameter”) –Phosphorus Pentachloride, is PCl 5 Hexa (6 to add, “hexagon”, “hexagonal”) –Uranium Hexaflouride, is UF 6


13 Single Element Ions Cations, positively (+) charged elements –From “cathode”, the negative battery pole –Positive (+) ions attracted to (-) cathode –Mostly metals which lost ≥1 electrons Na +, Ca 2+, Fe 3+, etc. Anions, negatively (-) charged elements –From “Anode”, the positive battery pole –Negative (-) ions attracted to (+) Anodes –Mostly non-metals which gained ≥1 electron Cl -, Br -, O 2-, etc.

14 Why the terms “Cation”, “Anion” ? Cations (+) attracted to Cathode (-) Anions (-) attracted to Anode (+)

15 What’s a Cathode … From the Greek work kathodos … “way down” Electrode where chemical reduction occurs, gain electrons. Cathodes emit electrons (diodes, CRT)



18 Why is the electron negative ? Benjamin Franklin responsible ! –Published kite in a storm experiment in 1780 Nobody really knew what electricity was A dangerous experiment, people killed repeating it –He applied terms “positive” and “negative” “Electrical Fluid” was term used at the time (+) and (-) Used for batteries, electrolysis Unfortunately “positive” is backwards –Assumption of flow (+) to (-) was wrong – … but we kept the polarity definitions –Electrons go the other way, are therefore (-) –See wikipedia on Benjamin Franklin

19 Element Ionic charges Alkali metals (1 st column) have single (+) charge –Na +, K +, Li + –Usually do NOT write the number for single charge Alkalai Earth metals (2 nd col.) have charge (+2) –Ca 2+, Mg 2+ Transition metals often have multiple valences –Iron can lose 2 or 3 electrons, Fe 2+ or Fe 3+ –Similar situation with Mn, Cr, Sn, etc. Old Latin names indicated degree of valence –“-ic” at end was/is highest valence state (mostly) But not always the same valence numerical value Ferric is +3, Stannic is +4 –“-ous” at end was/is lowest valence state (mostly) Not always the same numerical value

20 Formation of Compounds Binary Compounds –Cation + Anion  neutral molecule –Simple ratios = “law of multiple proportions” –Atom quantities must yield charge balance 2 Fe 3+ + 3 O 2-  Fe 2 O 3 H 2 SO 4  2H + + SO 4 2- –Molecules must be “real” materials Use multiplier to clear fractions (e.g. ½ O 2 )

21 Naming Compounds Binary Inorganic compounds –Compound name starts with an element name Same names & symbols on periodic chart Sodium (Na), Iron (Fe), Cadmium (Cd) –Cation element (+), then Anion (-) name Chlorine, oxygen, sulfur –Anion (-) in binary compound ends in –ide Sodium Chloride Iron Oxide, Cadmium Sulfide

22 Binary Halogen Acids For halogen acids, “hydro” is prefix used –Hydrochloric Acid = HCl –Avoids confusion with Chloric Acid = HClO 3 Binary Halogen Acids include –Hydrofluoric Acid = Hydrogen Fluoride = HF –Hydrochloric Acid = Hydrogen Chloride = HCl –Hydrobromic Acid = Hydrogen Bromide = HBr –Hydroiodic Acid = Hydrogen Iodide = HI

23 Formula Writing Cation first (usually a metal or hydrogen) –Hydrogen, H (valence +1) –Calcium, Ca (valence +2) –Aluminum, Al (valence +3) Anion follows (often a halogen, or gas) –Sulfur  Sulfide (valence -2) –Chlorine  Chloride (valence -1) –Oxygen  Oxide (valence -2) Add the two element names, formula is in atomic ratios –Hydrogen Sulfide, H 2 S ratio follows valence, 2:1 –Calcium Chloride, CaCl 2 ratio follows valence, 1:2 –Aluminum Oxide, Al 2 O 3 ratio follows valence, 2:3

24 Formula Writing Atomic ratios are simple numbers (1, 2, 3 …5) –Find a common denominator number for electrons –Multiply cation valence times anion valence Aluminum (+3) * Oxygen (-2) = 6 total electrons involved –Divide each valence into the common denominator 6/3 for aluminum = 2, 6/2 for oxygen =3 –These values are the ratios of the elements Al 2 O 3

25 Multi-Atom (poly atomic) molecules Many Anion combinations involve Oxygen –Nitrite, NO 2 1- Nitrate, NO 3 1- –Sulfite, SO 3 2- Sulfate, SO 4 2- –Carbonate, CO 3 2- BiCarbonate, HCO 3 1- –Chlorate, ClO 3 1- –Phosphate, PO 4 3- …. And a lot more !

26 Polyatomic Oxygen Anions Oxygen forms group around other elements –2, 3, 4 oxygen clusters surrounding another atom Stable configuration due to electron sharing –Sharing fills outer electron (valence) shell –“Octet Rule”, 8 is “magic number” for full shells –Shells of 8 creates exceptionally stable configuration Anion Groups exist with extra electrons –Gather as many as needed for full shells –“owning” or “sharing” electrons is equivalent Sharing is as good as ownership ! Excess electrons give ion a negative charge

27 Polyatomic ions, +1 charge Tetrahedral ammonium: N has 5 electrons, H has 1, total = 9 Total deployed is 8, so one “went missing”, charge is +1 Hydronium is proton (+1) attached to water, O=6 elect, H=1, total =9 Total deployed is 8, so one “went missing”, ionic charge is +1

28 Hydronium Ion

29 Polyatomic Anions, -1 charge For NO 3 1-, N has 5 electrons, O has 6, total is 18+5=23 Total deployed = 24, so 1 extra electron = -1 charge For NO 2 -1, N has 5 electrons, O has 6, total is 12+5=17 Total deployed = 18, so 1 extra electron = -1 charge

30 Polyatomic Anions, -2 charge For SO 4 2-, S has 6 electrons, O has 6, total is 5*6=30 Total deployed = 32, so 2 extra electron = -2 charge For SO 3 2-, S has 6 electrons, O has 6, total is 4*6 =24 Total deployed = 26, so 2 extra electrons = -2 charge

31 Preferred valence often the maximum Nitrite would rather be Nitrate –NO 2 - adds 1 oxygen, N goes (+3)  (+5) All valence electrons consumed at (+5) –Makes it useful as a preservative in sausage Nitrite consumes oxygen before the meat does Sulfite would rather be Sulfate –SO 3 - adds 1 oxygen, S goes (+4)  (+6) All valence electrons consumed at (+6) –Also a preservative, used in wine Sulfite consumes oxygen before the wine does Prevents wine into vinegar (until sulfite runs out)

32 Polyatomic Anions, Carbonate For CO 3 2-, C has 4 electrons, O has 6, total is 4+18=22 Total deployed = 24, so 2 extra electron = -2 charge For HCO 3 1-, C=4, 3O=18, H=1 so total =23 Total deployed = 24, so 1 extra electron = -1 charge

33 Polyatomic Anions, Phosphate For PO 4 3-, P has 5 electrons, O has 6, total is 5+24=29 Total deployed = 32, so 3 extra electron = -3 charge For HPO 4 2-, P=5 electrons, O=6, H=1, total is 5+24+1 =30 Total deployed = 32, so 2 extra electrons = -2 charge

34 Formula Writing Polyatomic ions behave like other anions –Cl -1, NO3 -1, SO4 -2 Use parenthesis around the polyatomic ion –Avoids confusion what multiple is involved –Ca(NO 3 ) 2 … not CaNO 32

35 Multiple Valence Cations Some elements have multiple valences –Lose up to all electrons in outer shell Old Latin names indicate valence –Fe ++, Fe(II), or Ferrous versus Fe +++, Fe(III), or Ferric –Sn ++, Sn(II), or Stannous versus Sn ++++, Sn(IV) or Stannic –Mn ++, Mn(II), or Managnous vs Mn ++++, Mn(IV), or Manganic –Cr ++, Cr(II), or Chromous versus Cr +++, Cr(III), or Chromic Latin Names not precise –No valence numbers, only words –Numeric values inconsistent

36 Oxides of Chlorine Chlorine an unusual case, (+) or (-) valence –As halogen it exhibits (-1) charge Due to gaining one electron to fill octet Valence is -1 in HCl, Hydrochloric Acid NaCl, CaCl 2, AlCl 3, etc. –Another possibility is to lose electrons Relatively unstable and reactive compounds –7electrons in outer shell, 5 more loosely held Valence is +1 in HClOHypochlorous acid Valence is +3 in HClO 2 Chlorous acid Valence is +5 in HClO 3 Chloric acid Valence is +7 in HClO 4 Perchloric acid



39 More on Latin Names xxx-”ic” acid yields xxx-”ate” anion –Nitric acid HNO 3 yields nitrate ion, NO 3 - –Sulfuric acid H 2 SO 4 yields sulfate ion, SO 4 2- –Chloric acid HClO 3 yields Chlorate ion, ClO 3 - –Originally the highest valence state observed xxx-”ous” acid yields xxx-”ite” anion –Nitrous acid HNO 2 yields nitrite ion, NO 2 - –Sulfurous acid H 2 SO 3 yields sulfite ion, SO 3 2- –Chlorous acid HClO 2 yields chlorite ion, ClO 2 - –Originally the lowest valence state observed

40 More on Latin Names What to do after finding MORE valence states than handled by ”ous” and ”ic” suffixes? Fix is more words to modify existing descriptors –“hypo” and ‘per” adopted to handle the situation “Hypo”-xxx means 1 less oxygen (below “ous”) –Chlorous acid is HClO 2 –Hypochlorous acid is HClO –Sodium Hypochorite (Chlorox) is NaClO “Per”-xxx means 1 more oxygen (beyond “ic”) –Chloric acid is HClO 3 –Perchloric acid is HClO 4`



43 What if it’s not in the text? Look for “family” relationships in columns –Sulfur and Selenium have similar properties they are both in periodic chart column 6A Sulfate is based on sulfur, SO 4 - - Selenium analog is “Selenate” SeO 4 - - Tellurium analog would be “Tellurate TeO 4 - - –Cesium is similar to Sodium, in column 1A Sodium Chloride is NaCl, Rubidium analog would be RbCl Cesium analog would be CsCl

44 Los Alamos National Laboratory's Periodic Table

45 Valence Naming Summary Latin Names: Ferrous, Ferric, Chromic,.. –Good = easy to say and type –Bad = inconsistent, no numbers to rely on Roman Numerals: Fe(III), Sn(IV) –Good = easy to type –Bad = clumsy to say, antiquated Roman Numbering Plus and Minus signs : Fe ++, SO 4 - - –Good = intuitive, fast to hand write, clarity –Bad = inconvenient to type, clumsy for large valence values Arabic character with sign: Fe 2+ –Good = intuitive, clarity, good for large valences –Bad = inconvenient to type Bottom Line … you will run into ALL of these –Be prepared !

46 Stopping point for 32A Now to the nomenclature dry lab We’ll use OLD manual, $6.50 at bookstore –Inexpensive because we print it in-house Page 58-69 in Fall 2009 edition –Pages 58-62 is background material –Pages 63-69 are the turn-in sheets –Work with partners, get a good start on each page so you know how to finish after lab. –Use Google, Wikipedia, other great web resources –Don’t copy from others, often a wrong answer source –Due next week

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