Naming Compounds Writing Formulas and Equations Larry Scheffler Lincoln High School

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.

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

Names of Polyatomic Ions with Oxygen ClO- hypochlorite ClO2- chlorite ClO3- chlorate ClO4- perchlorate NO2- Nitrite  NO3- Nitrate  PO33- phosphite  PO43- phosphate  SO32- SO42- sulfite  sulfate  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.

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

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-

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

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 – tetraphosphorous decoxide CO – carbon monoxide CO2 – carbon dioxide

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

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 as dinitrogen monoxide N2O3 =  Nitrogen (III) oxide    Since oxygen has a 2- charge, the nitrogen must be 3+ to balance the charges.  Also  known as dinitrogen trioxide

Binary compounds of Hydrogen The binary compounds of hydrogen are special cases. They were discovered before a convention was adopted and hence their original names have stayed. 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

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” Cl- Chloride HCl Hydrochloric Acid NO2- Nitrite HNO2 Nitrous Acid NO3- Nitrate HNO3 Nitric Acid SO32- Sulfite H2SO3 Sulfurous Acid SO42- Sulfate H2SO4 Sulfuric Acid PO33- Phosphite H3PO3 Phosphorous Acid PO43- Phosphate H3PO4 Phosphoric Acid CO32- Carbonate H2CO3 Carbonic Acid

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

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

Diatomic Molecules Hydrogen Fluorine Oxygen Iodine Chlorine Bromine H2 Nitrogen F2 Fluorine O2 Oxygen I2 Iodine Cl2 Chlorine Br2 Bromine 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

Diatomic Molecules Hydrogen Have Nitrogen No Fluorine Fear Oxygen Of 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 H2 Hydrogen Have N2 Nitrogen No F2 Fluorine Fear O2 Oxygen Of I2 Iodine Ice Cl2 Chlorine Cold Br2 Bromine Bunnies