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:
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 (H 2 O) Ethyl alcohol (C 2 H 6 O) Carbon dioxide (CO 2 ) Ozone (O 3 ) 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 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 AcidC 2 H 4 O 2 GlucoseC 6 H 12 O 6
Chemical Formulas Empirical Formula chemical formula that tells the smallest whole number ratio of each type of atom in a molecule NO 2 vs.N 2 O 4 HOvs.H 2 O 2 CH 2 vs.C 3 H 6
Ions and Ionic Compounds Some compounds are composed of ions instead of molecules. “Salt” (NaCl) contains Na + and Cl - ions Tums (CaCO 3 ) Contains Ca 2+ and CO 3 2- ions Milk of Magnesia [Mg(OH) 2 ] Contains Mg 2+ and OH -
Ions and Ionic Compounds Ions can be either monoatomic polyatomic Ions form when atoms (or groups of atoms) gain or lose electrons 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 - ) Ca 2+ (20p, 18e - ) [Ar: 18p,18e - ] O (8p, 8e - ) O 2- (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)
Ions and Ionic Compounds In general: Metal atoms lose e- and form cations. Nonmetal atoms gain e- and form anions. Common monoatomic ions Zn 2+ Ag + P 3-
Ions and Ionic Compounds Main group Fe 2+ Fe 3+ Cu + Cu 2+ Mn 2+ Mn 3+ Co 2+ Co 3+ Bi 3+ Bi 5+ Cr 2+ Cr 3+ Sn 2+ Sn 4+ Pb 2+ Pb 4+ Many transition metals and a few main group elements form more than one ion. 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: NO 3 - SO 4 2- HCO 3 - PO 4 3-
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 -
Ca 2+ + Cl - CaCl (2 pos, 1 neg) Ca Cl - CaCl 2 (2 pos, 2 neg) Ca 2+ Cl - Ca 2+ 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 Ca SO CaSO 4 F-F- Na + Ca 2+ SO 4 2- 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 Mg 1 Cl 2 MgCl 2 If the subscripts are not the lowest whole number ratio, divide them by the greatest common factor. Formulas of Ionic Compounds
Al 3 + O 2 - Example: Write the correct formula for a compound containing Al 3+ and O 2- ions Al 2 O 3 O 2- Al 3+ Formulas of Ionic Compounds
Al 3 + SO Example: Write the empirical formula for the compound formed from Al 3+ and SO 4 2- ions. Al 2 (SO 4 ) 3 SO 4 2- Al 3+ SO 4 2- Formulas of Ionic Compounds
Example: What are the empirical formulas for the compounds formed from: Ca 2+ and N 3- Sn 4+ and SO 4 2- Remember to use ( ) around polyatomic ions if you need more than one of them. Formulas of Ionic Compounds
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 Ca 2+ calcium ion Al 3+ 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 Fe 2+ iron (II) ion Fe 3+ iron (III) ion Cu + copper (I) ion Cu 2+ copper (II) ion
Naming Cations Two common polyatomic cations NH 4 + ammonium ion H 3 O + hydronium ion
Naming Anions Monoatomic anions drop the ending of the element’s name add “ide” NnitrogenN 3- nitride OoxygenO 2- oxide
Naming Anions Some simple polyatomic anions also use the “ide” ending OH - hydroxide CN - cyanide O 2 2- 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 NO 3 - nitrateSO 4 2- sulfate NO 2 - nitriteSO 3 2- 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 ClO 4 - perchlorate ClO 3 - chlorate ClO 2 - 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 ClO 3 - = chlorate ion BrO 3 - = bromate ion
Oxyanions Group 6 (S, Se, Te): The “ate” anion has 4 oxygens and a 2- charge SO 4 2- = sulfate SeO 4 2- = selenate Group 5 (N, P, As): The “ate” anion has 4 oxygens and a 3- charge except for Nitrogen PO 4 3- = phosphate NO 3 - = nitrate
Oxyanions Other common oxyanions that you must know: MnO 4 - = permanganate ion CrO 4 2- = chromate ion Cr 2 O 7 2- = dichromate ion
Oxyanions Anions derived by adding H + to an oxyanion: add “hydrogen” or “dihydrogen” as prefix to oxyanion name CO 3 2- carbonate HCO 3 - hydrogen carbonate (also called bicarbonate) PO 4 3- phosphate H 2 PO 4 - dihydrogen phosphate
Ionic Compounds Ionic compounds are named by: Cation name followed by anion name NaCl CaBr 2 NaClO Cu(NO 3 ) 2 sodium chloride calcium bromide sodium hypochlorite copper (II) nitrate
Examples Example: Write the names of these ionic compounds. Na 2 O FeCl 3 (NH 4 ) 3 PO 4 KClO 4 Pb(CO 3 ) 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 (NH 4 ) 2 SO 4 ammonium sulfate NH 4 + SO 4 2-
Writing Formulas from Names sodium bicarbonate barium nitrate sodium bromate iron(III) carbonate sodium hydrogen phosphate potassium dichromate tin (IV) oxide Example: Write the formulas for these ionic compounds
Names & Formulas of Acids Acid: a substance whose molecules form H + ions when dissolved in water HCl (aq) HCN (g) HClO 3 (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: HClO 4 = perchloric acid Change “ite” to “ous acid” Example: HClO 2 = 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 HNO 3 nitric acid HClO 4 perchloric acid HClO 3 chloric acid H 2 SO 4 sulfuric acid
Naming Acids You must know the names and formulas for the following acids for the exam: HF (aq)hydrofluoric acid H 2 S (g)hydrogen sulfide HCN (g)hydrogen cyanide HC 2 H 3 O 2 acetic acid H 2 CO 3 carbonic acid H 3 PO 4 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 Formula: HClO 4 perchlorate ClO 4 -
Binary Molecular Compounds Binary molecular compound: compound composed of molecules with two different types of atoms Remember: Many molecular compounds are composed strictly of non-metals. SO 2 N 2 O 4 H 2 OPCl 5 P 4 O 10 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 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. ______element name ______ element name with ide ending
Greek Prefixes PrefixMeaning mono1 di2 tri3 tetra4 penta5 hexa6 hepta7 octa8 nona9 deca10 You must know these!! P 4 S 10 = 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. N 2 O 4 PCl 5 NO 3
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: Ionicstarts with a metal or NH 4 Acidstarts with H or H n Binary Moleculartwo non-metals THEN use the appropriate naming system or method to write the formula.