Section 2-3: Writing Chemical formulas

Section 2.3—Chemical Formulas :Section 2.3—Chemical Formulas We need to be able to read the formulas for chemicals in the antacids!


Reminders from Section 2.2 :Your Appendix (Page A-2) has lists of: Common polyatomic ions Multivalent metals Covalent prefixes Use your periodic table to determine the charges of common elements when they form ions Reminders from Section 2.2


Ionic compounds :Ionic compounds


Definitions :Definitions Binary Ionic Compound- compound containing two elements—one metal and one non-metal + Cation - Anion Ionic bond- bond formed by attraction between + and - ions


Definition :Definition Polyatomic Ion- more than one atom that together have a charge + Cation Polyatomic Ionic Compound- compound containing at least one polyatomic ion


Metals & Non-Metals :Metals & Non-Metals Ionic Bonds are between metals & non-metals


Identifying & Naming Binary Ionic :These compounds: Contain a metal To write these formulas: Write the symbol & charge of the first element (the metal, cation). If there are roman numerals, that is the charge! Write the symbol & charge of the second element (the non-metal or polyatomic ion, 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. If adding a subscript to a polyatomic ion, use parenthesis. Identifying & Naming Binary Ionic


Example #1 :Example #1 Sodium chloride


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


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


Example #2 :Example #2 Calcium bromide


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


Example #2 :Example #2 Calcium bromide Cation Anion Ca+2 Br-1 CaBr2 Ca+2Br-1 +2 + -1 = +1 Ca+2Br-1Br-1 The subscript “2” is used to show that 2 anions are needed. +2 + -1 + -1 = 0


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


Let’s Practice :Let’s Practice CsCl K2O CaS Li3N Example: Write the following chemical formulas Cesium chloride Potassium oxide Calcium sulfide Lithium nitride


Example #3 :Example #3 Sodium carbonate


Example #3 :Example #3 Sodium carbonate Cation Polyatomic Anion Na+1 CO3-2


Example #3 :Example #3 Sodium carbonate Cation Polyatomic Anion Na+1 CO3-2 Na2CO3 Na+CO32- +1 + -2 = -1 Na+Na+CO32- The subscript “2” is used to show that 2 cations are needed. +1 + 1 + -2 = 0


Example #4 :Example #4 Magnesium nitrate


Example #4 :Example #4 Magnesium nitrate Cation Polyatomic Anion Mg+2 NO3-1


Example #4 :Example #4 Magnesium nitrate Cation Polyatomic Anion Mg+2 NO3-1 Mg(NO3)2 Use parenthesis when adding subscripts to polyatomic ions Mg+2NO3- +2 + -1 = 1 Mg+2NO3- NO3- The subscript “2” is used to show that 2 anions are needed. +2 + -1 + -1 = 0


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


Let’s Practice :Let’s Practice NaNO3 Ca(ClO3)2 K2SO3 Ca(OH)2 Example: Write the following chemical formulas Sodium nitrate Calcium chlorate Potassium sulfite Calcium hydroxide


Example #5 :Example #5 Iron (III) oxide


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


Example #5 :Example #5 Iron (III) oxide Cation Anion Fe+3 O-2 Fe2O3 Fe+3O2- +3 + -2 = -1 Fe+3Fe+3O2-O2-O-2 The subscript “2” and “3” are used to show the numbers of atoms needed. +3 + 3 + -2 + -2 + -2 = 0


Example #6 :Example #6 Copper (II) nitrate


Example #6 :Example #6 Copper (II) nitrate Cation Polyatomic Anion Cu+2 NO3-1


Example #6 :Example #6 Copper (II) nitrate Cation Polyatomic Anion Cu+2 NO3-1 Cu(NO3)2 Cu+2NO3- +2 + -1 = 1 Cu+2NO3-NO3- Use parenthesis when adding subscripts to a polyatomic ion +2 + -1 + -1 = 0


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


Let’s Practice :Let’s Practice Fe(NO3)2 CuCl Pb(OH)4 SnO Example: Write the following chemical formulas Iron (II) nitrate Copper (I) chloride Lead (IV) hydroxide Tin (II) oxide


Binary Covalent Compounds :Binary Covalent Compounds


Definition :Definition Binary Covalent Compound compound made from two non-metals that share electrons Non metal Non metal Covalent bond atoms share electrons


Identifying & Naming Binary Covalent :These compounds: Use covalent prefixes 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 :Example #7 Dinitrogen Tetraoxide


Example #7 :Example #7 Dinitrogen Tetraoxide N O “Di-” = 2 “Tetra-” = 4 N2O4


Example #8 :Example #8 Silicon dioxide


Example #8 :Example #8 Silicon dioxide Si O “Mono-” is not written for the first element “Di-” = 2 SiO2


CAUTION!!! :CAUTION!!! bi- di- Stands for “2” in covalent compounds Means there’s a hydrogen in the polyatomic anion “di” and “bi” do not mean the same thing! Carbon dioxide = CO2 Sodium biphosphate = Na2HPO4


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


Let’s Practice :Let’s Practice CO NO2 P2O5 Example: Write the following chemical formulas Carbon monoxide Nitrogen dioxide Diphosphorus pentaoxide


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


Mixed Practice :Mixed Practice Mg(OH)2 Cu(NO3)2 Fe2O3 NO2 NaHCO3 Example: Write the following chemical formulas Magnesium hydroxide Copper (II) nitrate Iron (III) oxide Nitrogen dioxide Sodium bicarbonate