Presentation on theme: "Molecules Most elements found in nature are not found as isolated atoms. Noble gases are common exceptions. Most natural materials are composed of either:"— Presentation transcript:
1 MoleculesMost elements found in nature are not found as isolated atoms.Noble gases are common exceptions.Most natural materials are composed of either:moleculesIonsMolecules and ions are both formed from atoms.
2 MoleculesMolecule:A group of atoms combined in definite proportions and held together by strong attractive forces called covalent chemical bondsCovalent bonds are formed when two atoms share two or more electronsThe smallest representative particle of a molecular compound
3 Molecular Compounds Molecular compounds composed of molecules that contain more than one type of atomExamples:Water (H2O)Ethyl alcohol (C2H6O)Carbon dioxide (CO2)Ozone (O3)Most molecular substances are composed of non-metals only.
4 Chemical Formulas Chemical Formula notation that describes the types and relative numbers of atoms in a pure substanceChemical formulas always contain:elemental symbolssubscriptsshow the relative number of each type of atom
5 Chemical Formulas Acetic Acid C2H4O2 Glucose C6H12O6 Molecular Formulaschemical formulas that tell the actual number of each type of atom in a moleculeprovide the greatest information about a compoundAcetic Acid C2H4O2Glucose C6H12O6
6 Chemical Formulas NO2 vs. N2O4 HO vs. H2O2 CH2 vs. C3H6 Empirical Formulachemical formula that tells the smallest whole number ratio of each type of atom in a moleculeNO2 vs. N2O4HO vs. H2O2CH2 vs. C3H6
7 Ions and Ionic Compounds Some compounds are composed of ions instead of molecules.“Salt” (NaCl)contains Na+ and Cl- ionsTums (CaCO3)Contains Ca2+ and CO32- ionsMilk of Magnesia [Mg(OH)2]Contains Mg2+ and OH-
8 Ions and Ionic Compounds Ions form when atoms (or groups of atoms) gain or lose electronsIons can be eithermonoatomicpolyatomicMonoatomic ion:a charged substance containing a single atom that has gained or lost electrons
9 Predicting Ionic Charge Many atoms gain or lose electrons in such a way that they end up with the same number of electrons as the nearest (closest in atomic number) noble gas.“octet” ruleCa (20p, 20e-) Ca2+ (20p, 18e-) [Ar: 18p,18e-]O (8p, 8e-) O2- (8p, 10e-) [Ne: 10p, 10e-]
10 Predicting Ionic Charge Using the octet rule you can easily determine the charge on most of the monoatomic ions formed by the main group elements.Main group metal cations:Charge = group numberMain group nonmetal anions:Charge = group # - 8(or simply count the number of “spaces” away from the nearest noble gas and add a negative sign)
11 Common monoatomic ions Ions and Ionic CompoundsCommon monoatomic ionsP3-Zn2+Ag+In general:Metal atoms lose e- and form cations.Nonmetal atoms gain e- and form anions.
12 Ions and Ionic Compounds Many transition metals and a few main group elements form more than one ion.Main groupFe2+Fe3+Cu+Cu2+Mn2+Mn3+Co2+Co3+Bi3+Bi5+Cr2+Cr3+Sn2+Sn4+Pb2+Pb4+Main group
13 Ions and Ionic Compounds Polyatomic ion:an electrically charged group of two or more atoms that are held together by covalent bondsPolyatomic ions cannot be broken into smaller piecesExamples:NO3-SO42-HCO3-PO43-
15 Common IonsYou are responsible for naming and writing formulas for compounds containing the ions shown in the Ion Chart given to you at the start of the semester.You should be able to write the names and formulas for binary molecular compounds and the common acids shown in this set of notes.You should also know the formulas and names of compounds that you use in the laboratory.
16 Ionic Compounds Ionic Compound a compound that contains both cations (+ charge) and anions (- charge)Ionic compounds generally contain a metal and one or more nonmetals.Molecular compounds generally contain nonmetals only.
17 Structures & Formulas of Ionic Compounds The ions in an ionic compound are arranged in a 3-D structure.There are no discrete molecules of an ionic compound.Ionic compounds are represented using empirical formulas
18 Formulas of Ionic Compounds Ionic compounds must be electrically neutral.Total positive charge = total negative chargeNa+ + Cl- NaCl (1 pos, 1 neg)Na+Cl-
20 Formulas of Ionic Compounds To write the empirical formula for an ionic compound:Determine the charge on each ion.Combine the ions in a ratio that gives electrically neutral compoundIf charges on the ions are equal in magnitude (but opposite in sign), then combine the ions in a 1:1 ratio.
21 Formulas of Ionic Compounds Na F- NaFNa+F-Ca SO42- CaSO4Ca2+SO42-
22 Formulas of Ionic Compounds If charges on the ions are different, then the charge of one ion becomes the subscript of the other ion.Mg+2 Cl -1 Mg1Cl2 MgCl2If the subscripts are not the lowest whole number ratio, divide them by the greatest common factor.
23 Formulas of Ionic Compounds Example: Write the correct formula for a compound containing Al3+ and O2- ionsAl2O3Al O 2-O2-O2-O2-Al3+Al3+
24 Formulas of Ionic Compounds Example: Write the empirical formula for the compound formed from Al3+ and SO42- ions.Al2(SO4)3Al3+ SO42-SO4 2-SO4 2-SO4 2-Al3+Al3+
25 Formulas of Ionic Compounds Example: What are the empirical formulas for the compounds formed from:Ca2+ and N3-Sn4+ and SO42-Remember to use ( ) around polyatomic ions if you need more than one of them.
26 Names & Formulas of Ionic Compounds Ionic compounds are named using the names of the ions that compose them.You must know the names and charges of all ions, including the polyatomic ions.Ion chart hand-outTrends discussed during lectureGeneral format for naming ionic compounds:Cation name followed by anion name
27 Naming CationsCations formed from metal ions have the same name as the metal.K+ potassium ionCa2+ calcium ionAl3+ aluminum ion
28 Naming CationsMany transition metals and a few main group metals can form more than one cation (i.e. two or more charges)the charge of the specific cation is given by Roman numeral in parentheses after the name of the metalFe2+ iron (II) ionFe3+ iron (III) ionCu+ copper (I) ionCu2+ copper (II) ion
29 Naming Cations Two common polyatomic cations NH4+ ammonium ion H3O+ hydronium ion
30 Naming Anions Monoatomic anions drop the ending of the element’s name add “ide”N nitrogen N3- nitrideO oxygen O2- oxide
31 Naming Anions Some simple polyatomic anions also use the “ide” ending OH- hydroxideCN- cyanideO22- peroxide
32 Naming OxyanionsOxyanions (polyatomic anions containing oxygen) have names ending in:“ate” most common oxyanionof the element“ite” same charge, 1 less ONO3- nitrate SO sulfateNO2- nitrite SO sulfite
33 Oxyanions (cont.) Prefixes are added if more than 2 oxyanions exist: “per” 1 more O than the “ate” oxyanion“hypo” 1 less O than the “ite” oxyanionClO4- perchlorateClO3- chlorateClO2- chloriteClO- hypochlorite
34 Oxyanions To learn & remember the names and formulas of the oxyanions: learn the name and formula for the “ate” oxyanionapply the rules discussed previously
35 OxyanionsThe names & formulas of the common oxyanions can be learned using trends within the same group of elements:Halogens:The “ate” anion has 3 oxygens and a 1- chargeClO3- = chlorate ionBrO3- = bromate ion
36 Oxyanions Group 6 (S, Se, Te): The “ate” anion has 4 oxygens and a 2- chargeSO42- = sulfateSeO42- = selenateGroup 5 (N, P, As):The “ate” anion has 4 oxygens and a 3- charge except for NitrogenPO43- = phosphateNO3- = nitrate
37 Oxyanions Other common oxyanions that you must know: MnO4- = permanganate ionCrO42- = chromate ionCr2O72- = dichromate ion
38 Oxyanions Anions derived by adding H+ to an oxyanion: add “hydrogen” or “dihydrogen” as prefix to oxyanion nameCO32- carbonateHCO3- hydrogen carbonate (also called bicarbonate)PO43- phosphateH2 PO4- dihydrogen phosphate
39 Ionic Compounds Ionic compounds are named by: Cation name followed by anion nameNaClCaBr2NaClOCu(NO3)2sodium chloridecalcium bromidesodium hypochloritecopper (II) nitrate
40 Examples Example: Write the names of these ionic compounds. Na2O FeCl3 (NH4)3PO4KClO4Pb(CO3)2
41 Writing Formulas from Names To write the correct empirical formula from the name of an ionic compound:Identify the symbol and charge for each ion.Determine the correct number of each ion needed to balance the charges.
42 Writing Formulas from Names Example: Write the empirical formula for ammonium sulfateammoniumsulfateNH4+(NH4)2SO4SO42-
43 Writing Formulas from Names Example: Write the formulas for these ionic compoundssodium bicarbonatebarium nitratesodium bromateiron(III) carbonatesodium hydrogen phosphatepotassium dichromatetin (IV) oxide
44 Names & Formulas of Acids Acid: a substance whose molecules form H+ ions when dissolved in waterHCl (aq)HCN (g)HClO3 (aq)Name of acid depends on the type of acid, its physical state, and the name of the anion.
45 Names & Formulas of Acids Three naming systems for acids:Acids containing oxygenAcids without oxygenaqueous solutionsgases
46 Naming Acids To name an acid: Does it have oxygen? Yes Write name of anionChange “ate” to “ic acid”Example:HClO4 = perchloric acidChange “ite” to “ous acid”HClO2 = chlorous acid
47 Naming Acids To name an acid: If no oxygen, is it (aq)? Yes Start with hydroAdd the name of anionChange “ide” to “ic acid”Example:HCl (aq) = hydrochloric acid
48 Naming Acids To name an acid: If no oxygen, is it (g)? Yes Start with hydrogenAdd the name of the anionExample:HCN (g) = hydrogen cyanide
49 Naming AcidsYou must know the names and formulas for the following acids for the exam:HCl (aq) hydrochloric acidHBr (aq) hydrobromic acidHI (aq) hydroiodic acidHNO3 nitric acidHClO4 perchloric acidHClO3 chloric acidH2SO4 sulfuric acid
50 Naming AcidsYou must know the names and formulas for the following acids for the exam:HF (aq) hydrofluoric acidH2S (g) hydrogen sulfideHCN (g) hydrogen cyanideHC2H3O2 acetic acidH2CO3 carbonic acidH3PO4 phosphoric acid
51 Writing Formulas for Acids Which category of acid is it?Oxyanion basedNot oxyanion based, (aq)Not oxyanion based, (g)Write the formula for the anion (including charge).Add enough H ions to make a neutral compound.
52 Example Example: Write the formula for perchloric acid. Category: oxyanion containing acidAnion: perchloric acid perchlorateClO4-Formula: HClO4
54 Binary Molecular Compounds compound composed of molecules with two different types of atomsRemember: Many molecular compounds are composed strictly of non-metals.SO2 N2O4H2O PCl5P4O10 CO
55 Binary Molecular Compounds The names of binary molecular compounds give both the type and number of each type of atom present.The general pattern for naming binary molecular compounds is:______element name ______ element name with ide ending
56 Binary Molecular Compounds ______element name ______ element name with ide endingThe first element is named using the name of the element.The second element is named using the “ide” ending.Greek prefixes are used to indicate the number of each type of element present.
57 Greek Prefixes Prefix Meaning mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 hepta 7octa 8nona 9deca 10You must know these!!P4S10 =tetraphosphorus decasulfide
58 Binary Molecular Compounds Special conventions for using Greek prefixes:Mono is never used with the first elementThe “a” or “o” in the prefix is dropped if the name of the element begins with a vowel.CO:carbon monooxidecarbon monoxide
59 Binary Molecular Compounds Example: Name the following compounds.N2O4PCl5NO3
60 Binary Molecular Compounds Example: Write the formulas for the following compounds.tetraphosphorus decoxidesulfur trioxidedisulfur dichloride
61 Naming — RevisitedBefore you can correctly name a compound or write its formula, YOU MUST determine which type of compound it is:Ionic starts with a metal or NH4Acid starts with H or HnBinaryMolecular two non-metalsTHEN use the appropriate naming system or method to write the formula.