Molecules Most elements found in nature are not found as isolated atoms. Noble gases are common exceptions. Most natural materials are composed of either: molecules Ions Molecules and ions are both formed from atoms.

Molecules Molecule: A group of atoms combined in definite proportions and held together by strong attractive forces called covalent chemical bonds Covalent bonds are formed when two atoms share two or more electrons The smallest representative particle of a molecular compound

Molecular Compounds Molecular compounds composed of molecules that contain more than one type of atom Examples: Water (H2O) Ethyl alcohol (C2H6O) Carbon dioxide (CO2) Ozone (O3) Most molecular substances are composed of non-metals only.

Chemical Formulas Chemical Formula notation that describes the types and relative numbers of atoms in a pure substance Chemical formulas always contain: elemental symbols subscripts show the relative number of each type of atom

Chemical Formulas Acetic Acid C2H4O2 Glucose C6H12O6 Molecular Formulas chemical formulas that tell the actual number of each type of atom in a molecule provide the greatest information about a compound Acetic Acid C2H4O2 Glucose C6H12O6

Chemical Formulas NO2 vs. N2O4 HO vs. H2O2 CH2 vs. C3H6 Empirical Formula chemical formula that tells the smallest whole number ratio of each type of atom in a molecule NO2 vs. N2O4 HO vs. H2O2 CH2 vs. C3H6

Ions and Ionic Compounds Some compounds are composed of ions instead of molecules. “Salt” (NaCl) contains Na+ and Cl- ions Tums (CaCO3) Contains Ca2+ and CO32- ions Milk of Magnesia [Mg(OH)2] Contains Mg2+ and OH-

Ions and Ionic Compounds Ions form when atoms (or groups of atoms) gain or lose electrons Ions can be either monoatomic polyatomic Monoatomic ion: a charged substance containing a single atom that has gained or lost electrons

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” rule Ca (20p, 20e-) Ca2+ (20p, 18e-) [Ar: 18p,18e-] O (8p, 8e-)  O2- (8p, 10e-) [Ne: 10p, 10e-]

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 number Main group nonmetal anions: Charge = group # - 8 (or simply count the number of “spaces” away from the nearest noble gas and add a negative sign)

Common monoatomic ions Ions and Ionic Compounds Common monoatomic ions P3- Zn2+ Ag+ In general: Metal atoms lose e- and form cations. Nonmetal atoms gain e- and form anions.

Ions and Ionic Compounds Many transition metals and a few main group elements form more than one ion. Main group Fe2+ Fe3+ Cu+ Cu2+ Mn2+ Mn3+ Co2+ Co3+ Bi3+ Bi5+ Cr2+ Cr3+ Sn2+ Sn4+ Pb2+ Pb4+ Main group

Ions and Ionic Compounds Polyatomic ion: an electrically charged group of two or more atoms that are held together by covalent bonds Polyatomic ions cannot be broken into smaller pieces Examples: NO3- SO42- HCO3- PO43-

Polyatomic Ions Some common polyatomic ions: Ammonium NH4+ Hydroxide OH- Cyanide CN- Nitrate NO3- Acetate C2H3O2- Sulfate SO42- Bisulfate (Hydrogen sulfate) HSO4- Carbonate CO32- Bicarbonate (Hydrogen carbonate) HCO3- Phosphate PO43-

Common Ions You 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.

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.

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

Formulas of Ionic Compounds Ionic compounds must be electrically neutral. Total positive charge = total negative charge Na+ + Cl- NaCl (1 pos, 1 neg) Na+ Cl-

Formulas of Ionic Compounds Ca2+ + Cl- CaCl (2 pos, 1 neg) Ca2+ Cl- Ca2+ + 2Cl- CaCl2 (2 pos, 2 neg) Ca2+ Cl- Cl-

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 compound If charges on the ions are equal in magnitude (but opposite in sign), then combine the ions in a 1:1 ratio.

Formulas of Ionic Compounds Na+ + F- NaF Na+ F- Ca2+ + SO42- CaSO4 Ca2+ SO42-

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 MgCl2 If the subscripts are not the lowest whole number ratio, divide them by the greatest common factor.

Formulas of Ionic Compounds Example: Write the correct formula for a compound containing Al3+ and O2- ions Al2O3 Al3+ O 2- O2- O2- O2- Al3+ Al3+

Formulas of Ionic Compounds Example: Write the empirical formula for the compound formed from Al3+ and SO42- ions. Al2(SO4)3 Al3+ SO42- SO4 2- SO4 2- SO4 2- Al3+ Al3+

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.

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-out Trends discussed during lecture General format for naming ionic compounds: Cation name followed by anion name

Naming Cations Cations formed from metal ions have the same name as the metal. K+ potassium ion Ca2+ calcium ion Al3+ aluminum ion

Naming Cations Many 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 metal Fe2+ iron (II) ion Fe3+ iron (III) ion Cu+ copper (I) ion Cu2+ copper (II) ion

Naming Cations Two common polyatomic cations NH4+ ammonium ion H3O+ hydronium ion

Naming Anions Monoatomic anions drop the ending of the element’s name add “ide” N nitrogen N3- nitride O oxygen O2- oxide

Naming Anions Some simple polyatomic anions also use the “ide” ending OH- hydroxide CN- cyanide O22- peroxide

Naming Oxyanions Oxyanions (polyatomic anions containing oxygen) have names ending in: “ate” most common oxyanion of the element “ite” same charge, 1 less O NO3- nitrate SO42- sulfate NO2- nitrite SO32- sulfite

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” oxyanion ClO4- perchlorate ClO3- chlorate ClO2- chlorite ClO- hypochlorite

Oxyanions To learn & remember the names and formulas of the oxyanions: learn the name and formula for the “ate” oxyanion apply the rules discussed previously

Oxyanions The 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- charge ClO3- = chlorate ion BrO3- = bromate ion

Oxyanions Group 6 (S, Se, Te): The “ate” anion has 4 oxygens and a 2- charge SO42- = sulfate SeO42- = selenate Group 5 (N, P, As): The “ate” anion has 4 oxygens and a 3- charge except for Nitrogen PO43- = phosphate NO3- = nitrate

Oxyanions Other common oxyanions that you must know: MnO4- = permanganate ion CrO42- = chromate ion Cr2O72- = dichromate ion

Oxyanions Anions derived by adding H+ to an oxyanion: add “hydrogen” or “dihydrogen” as prefix to oxyanion name CO32- carbonate HCO3- hydrogen carbonate (also called bicarbonate) PO43- phosphate H2 PO4- dihydrogen phosphate

Ionic Compounds Ionic compounds are named by: Cation name followed by anion name NaCl CaBr2 NaClO Cu(NO3)2 sodium chloride calcium bromide sodium hypochlorite copper (II) nitrate

Examples Example: Write the names of these ionic compounds. Na2O FeCl3 (NH4)3PO4 KClO4 Pb(CO3)2

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.

Writing Formulas from Names Example: Write the empirical formula for ammonium sulfate ammonium sulfate NH4+ (NH4)2SO4 SO42-

Writing Formulas from Names Example: Write the formulas for these ionic compounds sodium bicarbonate barium nitrate sodium bromate iron(III) carbonate sodium hydrogen phosphate potassium dichromate tin (IV) oxide

Names & Formulas of Acids Acid: a substance whose molecules form H+ ions when dissolved in water HCl (aq) HCN (g) HClO3 (aq) Name of acid depends on the type of acid, its physical state, and the name of the anion.

Names & Formulas of Acids Three naming systems for acids: Acids containing oxygen Acids without oxygen aqueous solutions gases

Naming Acids To name an acid: Does it have oxygen? Yes Write name of anion Change “ate” to “ic acid” Example: HClO4 = perchloric acid Change “ite” to “ous acid” HClO2 = chlorous acid

Naming Acids To name an acid: If no oxygen, is it (aq)? Yes Start with hydro Add the name of anion Change “ide” to “ic acid” Example: HCl (aq) = hydrochloric acid

Naming Acids To name an acid: If no oxygen, is it (g)? Yes Start with hydrogen Add the name of the anion Example: HCN (g) = hydrogen cyanide

Naming Acids You must know the names and formulas for the following acids for the exam: HCl (aq) hydrochloric acid HBr (aq) hydrobromic acid HI (aq) hydroiodic acid HNO3 nitric acid HClO4 perchloric acid HClO3 chloric acid H2SO4 sulfuric acid

Naming Acids You must know the names and formulas for the following acids for the exam: HF (aq) hydrofluoric acid H2S (g) hydrogen sulfide HCN (g) hydrogen cyanide HC2H3O2 acetic acid H2CO3 carbonic acid H3PO4 phosphoric acid

Writing Formulas for Acids Which category of acid is it? Oxyanion based Not oxyanion based, (aq) Not oxyanion based, (g) Write the formula for the anion (including charge). Add enough H ions to make a neutral compound.

Example Example: Write the formula for perchloric acid. Category: oxyanion containing acid Anion: perchloric acid  perchlorate ClO4- Formula: HClO4

Examples Acetic acid: Hydrochloric acid: Chloric acid: Hydrogen sulfide:

Binary Molecular Compounds compound composed of molecules with two different types of atoms Remember: Many molecular compounds are composed strictly of non-metals. SO2 N2O4 H2O PCl5 P4O10 CO

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

Binary Molecular Compounds ______element name ______ element name with ide ending The 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.

Greek Prefixes Prefix Meaning mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 hepta 7 octa 8 nona 9 deca 10 You must know these!! P4S10 = tetraphosphorus decasulfide

Binary Molecular Compounds Special conventions for using Greek prefixes: Mono is never used with the first element The “a” or “o” in the prefix is dropped if the name of the element begins with a vowel. CO: carbon monooxide carbon monoxide

Binary Molecular Compounds Example: Name the following compounds. N2O4 PCl5 NO3

Binary Molecular Compounds Example: Write the formulas for the following compounds. tetraphosphorus decoxide sulfur trioxide disulfur dichloride

Naming — Revisited Before 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 NH4 Acid starts with H or Hn Binary Molecular two non-metals THEN use the appropriate naming system or method to write the formula.