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Naming Compounds Writing Formulas and Equations

Naming Compounds Writing Formulas and Equations. Larry Scheffler Lincoln High School. Naming Compounds. The chemical formula represents the composition of each molecule.

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Naming Compounds Writing Formulas and Equations

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  1. Naming CompoundsWriting Formulasand Equations Larry Scheffler Lincoln High School

  2. Naming Compounds The chemical formula represents the composition of each molecule. In writing the chemical formula, in almost all cases the element farthest to the left of the periodic table is written first. So for example, the chemical formula of a compound that contains one sulfur atom and six fluorine atoms is SF6. If the two elements are in the same group, the symbol of the element of that is lower in the group (i.e. heavier) is written first e.g. IF3.

  3. Naming Ionic Compounds Ionic compounds are combinations of positive and negative ions. In writing the chemical formula, the positive ion is written first, It is then followed by the name of the negative ion. Monatomic anions end in ide. Special endings apply for polyatomic ions Examples NaCl Sodium chloride BaF2 Barium Fluoride ZnO Zinc Oxide

  4. Names of Polyatomic Ions with Oxygen • Polyatomic ions usually contain oxygen in addition to another element.  • Normally, they have a negative charge.  • They end in either "ate" or "ite" depending on the number of oxygen atoms present.

  5. Polyatomic Ion -- Exceptions • Most polyatomic ions contain oxygen • Their names end in “ite” or “ate”. • There are several exceptions: OH- hydroxide CN- cyanide SCN- thiocyanate

  6. Elements with Multiple Cations • When an element can form more than one cation, a Roman numeral is used to distinguish the oxidation state of the compound. • Iron, Tin, Lead, Copper, and are common elements with more than one cation. • Examples • PbSO4  =  lead (II) sulfate  This compound is formed from Pb2+ and  SO42- • Pb(SO4)2 =  lead (IV) sulfate  This compound is formed from Pb4+ and  SO42- • Fe(OH)2  =  iron (II) hydroxide  This compound is formed from Fe2+ and  OH- • Fe(OH)3  =  iron (III)  hydroxide  This compound is formed from Fe3+ and  OH-

  7. Examples of Ionic Compounds • NaCl = Sodium chloride • ZnF2 =Zinc fluoride • KOH = Potassium hydroxide • Ca(NO3)2 = Calcium nitrate • BaSO3 = Barium Sulfite • Al2(SO4) 3 = Aluminum sulfate • Ca3(PO3)2 = Calcium phosphite • NH4Cl = Ammonium chloride • (NH4)2CO3 = Ammonium carbonate

  8. Naming Covalent Compounds When naming covalent compounds, the name of the first element in the formula is unchanged. The suffix “-ide” is added to the second element. Often a prefix to the name of the second element indicates the number of the element in the compound Covalent molecules use prefixes; Ionic molecules use Roman Numerals (most of the time). Examples: SF6 – sulfur hexafluoride P4O10 – tetraphosphorousdecoxide CO – carbon monoxide CO2 – carbon dioxide

  9. Naming Covalent Compounds Greek Prefixes: Mono- Di- Tri- Tetra- Penta- Hexa- Hepta- Octa- Nona- Deca-

  10. Covalent molecules with multiple possibilities Example of exceptions: (not normally done, but you may come across) • A Roman Numeral is used to indicate the state of the more positive element • N2O   =  Nitrogen (I) oxide  Since oxygen has a 2- charge, the nitrogen must be 1+ to  balance the charges.    Also known asdinitrogenmonoxide • N2O3 =  Nitrogen (III) oxide   Since oxygen has a 2- charge, the nitrogen must be 3+ to balance the charges.  Also  known as dinitrogentrioxide

  11. Binary compounds of Hydrogen Water H2O is not called dihydrogen monoxide • Hydrogen forms binary compounds with almost all non-metals except the noble gases. • Examples • HF - hydrogen fluoride • HCl - hydrogen chloride • H2S - hydrogen sulfide The binary compounds of hydrogen are special cases. They were discovered before a convention was adopted and hence their original names have stayed.

  12. Acids When many hydrogen compounds are dissolve in water they take on the form of an acid. Special rules apply to acids. The “ide” suffix becomes “hydro” “-ic”, The “ite” suffix becomes “ous” The “ate” suffix becomes “ic”

  13. Writing Formulas for Ionic Compounds • Write the positive ion (cation) first, then the negative ion. • The positive charges must balance the negative charges. • Use subscripts to show how many times each ion must appear in order for the charges to balance. A subscript is not used if the ion appears only once. (Crisscross Method) • Use parenthesis around polyatomic ions that appear more than once in the formula

  14. Examples • Na+ and Cl- = NaCl • Zn2+ and Br- = ZnBr2 • K+ and OH- = KOH • Ca2+ and OH- = Ca(OH)2 • Fe2+ and SO42- = FeSO4 • Fe3+ and SO42- = Fe2(SO4) 3 • Ca2 + and PO43- = Ca3(PO4)2 • NH4+ and Cl- = NH4Cl • NH4+ and CO32- = (NH4)2CO3

  15. Diatomic Molecules • Certain elements exist as diatomic molecules in nature • The “Seven at 7” • Starting at #7, in the shape of a 7 (sort of), there are 7 elements

  16. Diatomic Molecules • Certain elements exist as diatomic molecules in nature • The “Seven at 7” • Starting at #7, in the shape of a 7 (sort of), there are 7 elements

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