CHEMICAL COMPOUNDS & CHEMICAL FORMULAS

Transcription

1 Chemical Names and Formulas CHAPTER 7 CHEMICAL COMPOUNDS & CHEMICAL FORMULAS Everyday chemicals that we use are given common names. These common names don t tell us anything about the actual chemical composition of the compound. Nomenclature systems allow for us to use the most accurate name for chemicals. Significance of a Formula Recall: a formula tells the type and the numbers of atoms Monatomic Ions Recall: Cations have very low ionization energies [energies needed to lose an electron], while anions have very high electron affinities [energy needed to add an electron]. The goal for elements is to reach a noble-gas configuration. Noble-gas configuration = STABILITY!

2 Monatomic Cations Members of Group 1 tend to lose 1 electron in order to get back to a noble-gas configuration. This results in a 1+ charge. Members of Group 2 lose 2 electrons in order to get back to a noble-gas configuration. This results in a 2+ charge. Members of Group 13 lose 3 electrons to get to a noble-gas configuration, resulting in a 3+ charge. Monatomic Anions Starting with Group 15, elements begin to gain electrons in order to reach noble-gas configuration. Group 15 = 3- charge [gain of 3 electrons] Group 16 = 2- charge [gain of 2 electrons] Group 17 = 1- charge [gain of an electron] There are some elements on the periodic table that can have multiple charges (positive), see the transition metals in the middle of the PT. Naming Monatomic Ions When naming cations, the name of the cation is the same as the metal s name. When naming anions, the name of the anion is changed by adding the suffix ide. When an element can have multiple charges, we must use the Stock system. The Stock system uses Roman numerals in parenthesis to indicate the charge of the cation. The Notorious B.I.C. (Binary Ionic Compound) Binary ionic compounds are compounds composed of 2 different elements. As a general rule, the total + charge must equal the total charge. When writing the formulas for BICs, follow the following steps. 1. Write ions side by side with cation first. 2. Criss-cross charge to make subscripts. 3. Check to see if subscripts are in lowest terms. Remember, + must = -!

3 Writing Chemical Formulas Practice Write the formula of the binary ionic compound that will result between the following elements: 1. zinc and sulfur 2. aluminum and phosphorus 3. strontium and chlorine 4. barium and oxygen 5. sodium and nitrogen 6. lithium and iodine Naming BICs When naming BICs, we name the cation (metal) first, then the anion (nonmetal). Examples: 1. Sr 3 N 2 2. AgCl 3. NaI 4. CaO Naming BICs Practice Name the following BICs indicated by the following formulas: 1. AgBr 2. ZnO 3. CaBr 2 4. MgO 5. AlP Naming BICs Using Stock System Name the following BICs according to the Stock system: 1. CuO 2. SnS 3. Fe2O3 4. FeO 5. PbCl2 6. VO

4 Polyatomic Ions Polyatomic ions are ions that are composed of more than one type of atom. Almost all polyatomic ions are negatively charged, except the ammonium ion [NH 4+ ]. A majority of polyatomic ions are called oxyanions. Oxyanions are polyatomic ions that contain oxygen. Nomenclature of Polyatomic Ions We can make several different polyatomic ions from the same two elements. Ex. N & O Nitrite = NO 2- Nitrate = NO 3- The suffix ite goes with the anion with the lower number of oxygen atoms. The suffix ate goes with the anion with the higher number of oxygen atoms. Nomenclature of Polyatomic Ions (cont d) Sometimes, we may have to use prefixes when we have more than 2 possible anions. Ex. Chlorine & oxygen ClO 4 - = perchlorate ClO 3 - = chlorate ClO 2 - = chlorite ClO - = hypochlorite The prefix per- is used for the highest number of oxygen atoms; whereas, the prefix hypo- is used for the lowest number of oxygen atoms. Writing Formulas Using Polyatomic Ions When writing formulas for compounds using polyatomic ions, we follow the same steps as BICs. 1. Write ions side by side cation first! 2. Criss-cross charges to make subscripts.* 3. Check to see if subscripts are in lowest terms. *There is only a slight difference: If we crisscross and the subscript for the polyatomic ion is greater than one, then we must put the polyatomic ion in parentheses.

5 Writing Formulas Practice Write formulas for the following ionic compounds: 1. lithium nitrate 2. copper (II) sulfate 3. potassium perchlorate 4. ammonium chloride 5. lead (IV) phosphate 6. tin (IV) oxalate 7. ammonium carbonate Naming Compounds Using Polyatomic Ions When naming ionic compounds using polyatomic ions, the rules are the same. Cation goes first, followed by anion. We don t have to change the ending of the polyatomic since the majority of them are anions. Naming Compounds Practice Give the names of the following ionic compounds: 1. NaCH 3 COO 2. SrCO 3 3. Ba 3 (PO 4 ) 2 Binary Molecular Compounds (BMCs) Different from BICs contain 2 nonmetal atoms Nomenclature system uses Greek numerical prefixes PREFIXES *Use mono- only for second word 4. AgNO 3 5. Cu(ClO 4 ) 2 1 mono- 2 di- 3 tri- 4 tetra- 5 penta- 6. Al 2 (SO 4 ) 3 7. KCN 6 hexa- 7 hepta- 8 octa- 9 nona- 10 deca-

6 Naming BMCs Practice Give the names of the following binary molecular compounds: 1. SO 3 2. CO 2 3. N 2 O 5 4. As 2 O 5 5. PBr 5 6. SF 6 7. ICl 3 Writing BMC Formulas Practice Write the formulas for the following compounds: 1. oxygen difluoride 2. carbon tetraiodide 3. phosphorus trichloride 4. dinitrogen monoxide 5. disilicon hexabromide 6. diphosphorus trioxide 7. disulfur dichloride