Chapter 7 Chemical Formulas and Chemical Compounds Section 1— Determining Chemical Formulas from Names of Compounds

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 “B” Chemical Names and Formulas

Writing Chemical Formulas for Binary Ionic Compounds

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

Metals & Non-Metals Ionic Bonds are between metals & non-metals HHe LiBeBCNOFNe NaMgAlSiPSClAr KCaScTiVCrMnFeCoNiCuZnGaGeAsSeBrKr RbSrYZrNbMoTcRuRhPdAgCdInSnSbTeIXe CsBaLuHfTaWReOsIrPtAuHgTlPbBiPoAtRn FrRaLrRfDbSgBhHsMtUunUuuUubUut MetalsMetalloids Non- metals

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

Example #1 Sodium chloride

Example #1 Sodium chloride Cation Anion Na +1 Cl -1 NaCl

Example #1 Sodium chloride Cation Anion Na +1 Cl -1 NaCl Na +1 Cl = 0 The compound is neutral…no subscripts are needed.

Example #2 Calcium bromide

Example #2 Calcium bromide Cation Anion Ca +2 Br -1

Example #2 Calcium bromide Cation Anion Ca +2 Br -1 CaBr 2 Ca +2 Br = +1 Ca +2 Br -1 Br -1 The subscript “2” is used to show that 2 anions are needed = 0

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

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

Let’s Practice Example: Write the following chemical formulas Cesium chloride Potassium oxide Calcium sulfide Lithium nitride

Let’s Practice CsCl K2OK2O CaS Li 3 N Example: Write the following chemical formulas Cesium chloride Potassium oxide Calcium sulfide Lithium nitride

Writing Chemical Formulas for Polyatomic Ionic Compounds

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

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

Naming Polyatomic Ionic Compounds Or, use the crossover method described for binary ionic compounds

Example #3 Sodium carbonate

Example #3 Sodium carbonate Cation Polyatomic Anion Na +1 CO 3 -2

Example #3 Sodium carbonate Cation Polyatomic Anion Na +1 CO 3 -2 Na 2 CO 3 Na + CO = -1 Na + Na + CO 3 2- The subscript “2” is used to show that 2 cations are needed = 0

Example #4 Magnesium nitrate

Example #4 Magnesium nitrate Cation Polyatomic Anion Mg +2 NO 3 -1

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 = 1 Mg +2 NO 3 - NO 3 - The subscript “2” is used to show that 2 anions are needed = 0

Let’s Practice Example: Write the following chemical formulas Sodium nitrate Calcium chlorate Potassium sulfite Calcium hydroxide

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

Writing Chemical Formulas for Ionic Compounds with Multivalent Metals

Definition Reminder Multivalent Metal- metal that has more than one possibility for cationic charge Examples: Fe2+ iron ( II ) Fe3+ iron ( III )

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

Example #5 Iron (III) oxide

Example #5 Iron (III) oxide Cation Anion Fe +3 O -2

Example #5 Iron (III) oxide Cation Anion Fe +3 O -2 Fe 2 O 3 Fe +3 O = -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 = 0

Example #6 Copper (II) nitrate

Example #6 Copper (II) nitrate Cation Polyatomic Anion Cu +2 NO 3 -1

Example #6 Copper (II) nitrate Cation Polyatomic Anion Cu +2 NO 3 -1 Cu(NO 3 ) 2 Cu +2 NO = 1 Cu +2 NO 3 - NO 3 - Use parenthesis when adding subscripts to a polyatomic ion = 0

Let’s Practice Example: Write the following chemical formulas Iron (II) nitrate Copper (I) chloride Lead (IV) hydroxide Tin (II) oxide

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

Writing Chemical Formulas for Binary Covalent Compounds

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

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!

Example #7 Dinitrogen Tetraoxide

Example #7 Dinitrogen Tetraoxide N O “Di-” = 2 “Tetra-” = 4 N2O4N2O4

Example #8 Silicon dioxide

Example #8 Silicon dioxide Si O “Mono-” is not written for the first element “Di-” = 2 SiO 2

Let’s Practice Example: Write the following chemical formulas Carbon monoxide Nitrogen dioxide Diphosphorus pentaoxide

Let’s Practice CO NO 2 P 2 O 5 Example: Write the following chemical formulas Carbon monoxide Nitrogen dioxide Diphosphorus pentaoxide

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

Mixed Practice Example: Write the following chemical formulas Magnesium hydroxide Copper (II) nitrate Iron (III) oxide Nitrogen dioxide Sodium bicarbonate

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

Writing Chemical Formulas for Binary & Oxyacids

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

Example #4 Hydrofluoric acid

Example #4 Hydrofluoric acid Hydrogen cation Does not contain oxygen H +1 F -1 HF H +1 F = 0 The compound is neutral. Subscripts are not needed

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)

Example #5 Carbonic acid

Example #5 Carbonic acid Hydrogen cation From the “___ate” anion H +1 CO 3 -2

Example #5 Carbonic acid Hydrogen cation From the “___ate” anion H +1 CO 3 -2 H 2 CO 3 H + CO = -1 H + H + CO = 0

Example #6 Nitrous acid

Example #6 Nitrous acid Hydrogen cation From the “___ite” anion H +1 NO 3 -1

Example #6 Nitrous acid Hydrogen cation From the “___ite” anion H +1 NO 3 -1 HNO 2 H + NO = 0

Let’s Practice Example: Write the formula for the following acids Phosphoric acid Hydroiodic acid Carbonous acid Perchloric acid

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