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Chapter 7 Chemical Formulas and Chemical Compounds Section 1— Determining Chemical Formulas from Names of Compounds
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In the previous set of powerpoints for Section 7.1 we learned how to write chemical names from chemical formulas Now, we need to write chemical formulas given chemical names For help with writing chemical formulas, please remember to use your periodic table to determine the charges of common elements when they form ions the common monoatomic ion chart on p. 221, and the common polyatomic ion chart on p. 226 7.1 “B” Chemical Names and Formulas
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Writing Chemical Formulas for Binary Ionic Compounds
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Definition Reminders Binary Ionic Compound- compound containing two elements—one metal and one non-metal + Cation + Cation - Anion - Anion Ionic Compound Ionic bond- bond formed by attraction between + and - ions
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Metals & Non-Metals Ionic Bonds are between metals & non-metals HHe LiBeBCNOFNe NaMgAlSiPSClAr KCaScTiVCrMnFeCoNiCuZnGaGeAsSeBrKr RbSrYZrNbMoTcRuRhPdAgCdInSnSbTeIXe CsBaLuHfTaWReOsIrPtAuHgTlPbBiPoAtRn FrRaLrRfDbSgBhHsMtUunUuuUubUut MetalsMetalloids Non- metals
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Binary ionic compounds: End in “-ide” (except “hydroxide and cyanide”) Do NOT contain covalent prefixes To write formulas for binary ionic compounds: Write the symbol & charge of the first element (the metal, cation) Write the symbol & charge of the second element (the non-metal, anion) Add more of the cations and/or anions to have a neutral compound Use subscripts to show how many of each type of ion is there. Identifying & Naming Binary Ionic Compounds
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Example #1 Sodium chloride
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Example #1 Sodium chloride Cation Anion Na +1 Cl -1 NaCl
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Example #1 Sodium chloride Cation Anion Na +1 Cl -1 NaCl Na +1 Cl -1 +1 + -1 = 0 The compound is neutral…no subscripts are needed.
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Example #2 Calcium bromide
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Example #2 Calcium bromide Cation Anion Ca +2 Br -1
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Example #2 Calcium bromide Cation Anion Ca +2 Br -1 CaBr 2 Ca +2 Br -1 +2 + -1 = +1 Ca +2 Br -1 Br -1 The subscript “2” is used to show that 2 anions are needed. +2 + -1 + -1 = 0
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Naming Binary Ionic Compounds Another method used to write the chemical formulas for binary ionic compounds is the “crossover” method Write the symbols for the ions side by side/Write the cation first Cross over the charges by using the absolute value of each ion’s charge as the subscript for the other ion give subscripts Check the subscripts and divide them by their largest common facto to give the smallest whole number ratio of ions, then write the formula
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Naming Binary Ionic Compounds Aluminum Oxide Al 3+ O 2- Al 2 3+ O 3 2- (2)(+3) + (3)(-2) = 0 Al 2 O 3
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Let’s Practice Example: Write the following chemical formulas Cesium chloride Potassium oxide Calcium sulfide Lithium nitride
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Let’s Practice CsCl K2OK2O CaS Li 3 N Example: Write the following chemical formulas Cesium chloride Potassium oxide Calcium sulfide Lithium nitride
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Writing Chemical Formulas for Polyatomic Ionic Compounds
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Definition Reminders Polyatomic Ionic Compound compound containing at least one polyatomic ion + Cation + Cation - Polyatomic Anion Polyatomic Ionic Compound OR - Anion - Anion + Polyatomic Cation Polyatomic Ionic Compound + Polyatomic Cation Polyatomic Ionic Compound OR - Polyatomic Anion
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Polyatomic ionic compounds: Most do not end with “-ide” exceptions include hydroxide & cyanide Do not use covalent prefixes To write formulas for polyatomic ionic compounds: Write the symbol & charge of the cation & anion Add additional cations or anions to have a neutral compound Use subscripts to show the number of ions When using subscripts with a polyatomic ion, you must put the polyatomic ion in parenthesis. Identifying & Naming Polyatomic Ionic Compounds
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Naming Polyatomic Ionic Compounds Or, use the crossover method described for binary ionic compounds
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Example #3 Sodium carbonate
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Example #3 Sodium carbonate Cation Polyatomic Anion Na +1 CO 3 -2
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Example #3 Sodium carbonate Cation Polyatomic Anion Na +1 CO 3 -2 Na 2 CO 3 Na + CO 3 2- +1 + -2 = -1 Na + Na + CO 3 2- The subscript “2” is used to show that 2 cations are needed. +1 + 1 + -2 = 0
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Example #4 Magnesium nitrate
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Example #4 Magnesium nitrate Cation Polyatomic Anion Mg +2 NO 3 -1
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Example #4 Magnesium nitrate Cation Polyatomic Anion Mg +2 NO 3 -1 Mg(NO 3 ) 2 Use parenthesis when adding subscripts to polyatomic ions Mg +2 NO 3 - +2 + -1 = 1 Mg +2 NO 3 - NO 3 - The subscript “2” is used to show that 2 anions are needed. +2 + -1 + -1 = 0
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Let’s Practice Example: Write the following chemical formulas Sodium nitrate Calcium chlorate Potassium sulfite Calcium hydroxide
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Let’s Practice NaNO 3 Ca(ClO 3 ) 2 K 2 SO 3 Ca(OH) 2 Example: Write the following chemical formulas Sodium nitrate Calcium chlorate Potassium sulfite Calcium hydroxide
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Writing Chemical Formulas for Ionic Compounds with Multivalent Metals
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Definition Reminder Multivalent Metal- metal that has more than one possibility for cationic charge Examples: Fe2+ iron ( II ) Fe3+ iron ( III )
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Ionic compounds with multivalent metals: Will have Roman numerals To write chemical formulas for these compounds: Same rules as binary ionic or polyatomic ionic. The Roman numerals tell the charge of the metal (cation) Identifying & Naming Compounds with Multivalent Metals
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Example #5 Iron (III) oxide
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Example #5 Iron (III) oxide Cation Anion Fe +3 O -2
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Example #5 Iron (III) oxide Cation Anion Fe +3 O -2 Fe 2 O 3 Fe +3 O 2- +3 + -2 = -1 Fe +3 Fe +3 O 2- O 2- O 2- The subscript “2” and “3” are used to show the numbers of atoms needed. +3 + 3 + -2 + -2 + -2 = 0
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Example #6 Copper (II) nitrate
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Example #6 Copper (II) nitrate Cation Polyatomic Anion Cu +2 NO 3 -1
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Example #6 Copper (II) nitrate Cation Polyatomic Anion Cu +2 NO 3 -1 Cu(NO 3 ) 2 Cu +2 NO 3 - +2 + -1 = 1 Cu +2 NO 3 - NO 3 - Use parenthesis when adding subscripts to a polyatomic ion +2 + -1 + -1 = 0
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Let’s Practice Example: Write the following chemical formulas Iron (II) nitrate Copper (I) chloride Lead (IV) hydroxide Tin (II) oxide
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Let’s Practice Fe(NO 3 ) 2 CuCl Pb(OH) 4 SnO Example: Write the following chemical formulas Iron (II) nitrate Copper (I) chloride Lead (IV) hydroxide Tin (II) oxide
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Writing Chemical Formulas for Binary Covalent Compounds
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Definition Reminders Binary Covalent Compound compound made from two non-metals that share electrons Non metal Non metal Non metal Non metal Covalent compound Covalent bond atoms share electrons
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Binary covalent compounds: Use covalent prefixes (mono, di, tri, tetra, etc) To write these formulas: Write the symbols of the first and second element Use the covalent prefixes (assume the first element is “1” if there’s no prefix) as the subscripts to show number of atoms. Identifying & Naming Binary Covalent Atoms do not form charges when bonding covalently…you DO NOT need to worry about charges with this type!
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Example #7 Dinitrogen Tetraoxide
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Example #7 Dinitrogen Tetraoxide N O “Di-” = 2 “Tetra-” = 4 N2O4N2O4
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Example #8 Silicon dioxide
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Example #8 Silicon dioxide Si O “Mono-” is not written for the first element “Di-” = 2 SiO 2
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Let’s Practice Example: Write the following chemical formulas Carbon monoxide Nitrogen dioxide Diphosphorus pentaoxide
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Let’s Practice CO NO 2 P 2 O 5 Example: Write the following chemical formulas Carbon monoxide Nitrogen dioxide Diphosphorus pentaoxide
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Nomenclature Summary Writing Chemical Formulas Does not contain covalent prefixes Ends with “-ide” (except hydroxide & cyanide) = Binary Ionic All others = Polyatomic Ionic Does contain covalent prefixes = Binary Covalent compound
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Mixed Practice Example: Write the following chemical formulas Magnesium hydroxide Copper (II) nitrate Iron (III) oxide Nitrogen dioxide Sodium bicarbonate
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Mixed Practice Mg(OH) 2 Cu(NO 3 ) 2 Fe 2 O 3 NO 2 NaHCO 3 Example: Write the following chemical formulas Magnesium hydroxide Copper (II) nitrate Iron (III) oxide Nitrogen dioxide Sodium bicarbonate
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Writing Chemical Formulas for Binary & Oxyacids
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To write these formulas: The cation is H +1 Write the anion and charge Balance the charges by adding the appropriate subscript to the hydrogen cation 7.1 Chemical Names & Formulas / Identifying & Naming Binary Acids
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Example #4 Hydrofluoric acid
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Example #4 Hydrofluoric acid Hydrogen cation Does not contain oxygen H +1 F -1 HF H +1 F -1 +1 + -1 = 0 The compound is neutral. Subscripts are not needed
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To write these formulas: The cation is H +1 If it is an “-ic” acid, the anion is the “-ate” polyatomic ion If it is an “-ous” acid, the anion is the “-ite” polyatomic ion Add subscript to the hydrogen cation to balance charges 7.1 Chemical Names & Formulas / Identifying & Naming Oxyacids (“Non-Hydro” Acids)
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Example #5 Carbonic acid
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Example #5 Carbonic acid Hydrogen cation From the “___ate” anion H +1 CO 3 -2
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Example #5 Carbonic acid Hydrogen cation From the “___ate” anion H +1 CO 3 -2 H 2 CO 3 H + CO 3 2- +1 + -2 = -1 H + H + CO 3 2- +1 + 1 + -2 = 0
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Example #6 Nitrous acid
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Example #6 Nitrous acid Hydrogen cation From the “___ite” anion H +1 NO 3 -1
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Example #6 Nitrous acid Hydrogen cation From the “___ite” anion H +1 NO 3 -1 HNO 2 H + NO 2 - +1 + -1 = 0
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Let’s Practice Example: Write the formula for the following acids Phosphoric acid Hydroiodic acid Carbonous acid Perchloric acid
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Phosphoric acid Hydroiodic acid Carbonous acid Perchloric acid Let’s Practice H 3 PO 4 HI H 2 CO 2 HClO 4 Example: Write the formula for the following acids
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