WRITING FORMULAS AND NAMING COMPOUNDS IONIC COMPOUNDS

Transcription

1 WRITING FORMULAS AND NAMING COMPOUNDS IONIC COMPOUNDS One of the most important concepts to understand when naming and writing ionic compounds is the concept of charge. You must be able to predict which ions will have which charge. Therefore, let s have a little review! Fill in the charge (or charges) for each of the following groups. Group Metal or Non-Metal? Lose or Gain Electrons? Charge(s)? Group 1 Metal Lose 1 electron Group 2 Metal Lose 2 electrons Group 13 Metal Lose 3 electrons Group 14 Non-Metal Metal Gain 4 electrons Lose 2 or 4 electrons Group 15 Non-Metal Gain 3 electrons Group 16 Non-Metal Gain 2 electrons Group 17 Non-Metal Gain 1 electron We also have three elements in the transition metal section which always have a set charge. You will eventually need to make sure you have these memorized. Ag +1 Zn +2 Cd +2 A. Binary Ionic Compounds Binary means 2 types of elements! Not 2 total atoms. Now that you know which elements have which charge, we are ready to start writing formulas of ionic compounds! The goal of ionic compounds is to make electrons lost equal electrons gained or, in other words, TO MAKE CHARGES CANCEL OUT. Therefore, you might need more than one of an element to make them cancel!

2 If you need more than one of an element, you will use a subscript to indicate how many you need. We do not show a subscript if only one of that element is needed. Also, in the final formula, charges are not shown the subscripts are indicating that charges are canceling out, so we don t need to show them! Remember -ide means single element anion EXCEPT hydroxide and cyanide Notice no charges are shown in the final compound! Elements Ions Make Charges Cancel! Final Formula Calcium chloride Ca +2 and Cl = 0 (need 1 Ca +2 and 2 Cl -1 ) Aluminum oxide Al +3 and O = 0 (need 2 Al +3 and 3 O -2 ) CaCl 2 Al 2 O 3 Lithium fluoride Magnesium phosphide Zinc iodide Gallium bromide Potassium sulfide Silver bromide NOTICE HOW CATIONS (metals) GO FIRST AND ANIONS (non-metals) GO SECOND! We always write the positive ions first and the negative ions second. We name in the same order as well. IONS before ANIONS! Now, let s talk about how to name compounds! For BINARY (2-element) ionic compounds where there is only one possible charge for the element, this process is very easy. Simply name the metal, then name the non-metal with an ide ending.

3 Formula Name CaCl 2 Calcium chloride Al 2 O 3 Na 2 O BaI 2 B. Binary Ionic Compounds WITH those WEIRD Transition metals! So far, we ve only looked at ionic compounds where the elements have only one possible charge for their ions. However, we have several metals that can have more than one charge for their ions! The metals that like to have more than one charge for their ions are most of the transition metals, and the metals of groups 14 and 15. Therefore, we need to show which charge was used for the metal when we write the name of the compound. We do this by placing the charge of the metal as a roman numeral directly after the metal s name. We name the non-metal with the ide ending. Find the final formula for each compound. These examples are using elements that have more than one possible charge for the metal ion. But why is there no roman numeral charge for the oxide? The (III) tells us that iron has a +3 charge! Because oxygen only has one possible charge for his ion! Compound Ions Make Charges Cancel! Final Formula Iron (III) oxide Fe +3 and O = 0 (need 2 Fe +3 and 3 O -2 ) Fe 2 O 3 Tin (IV) chloride Lead (IV) oxide

4 Now that you ve seen how the roman numerals work in the forward direction, it s time to try it out in the backwards direction. This gets a little bit harder. First, when you see an ionic compound, identify if the metal has more than one possible charge or not. If it does have more than one possible charge, use the non-metal to figure out the charge of the metal. Remember, charges must cancel out to zero! Then, to name the compound, (1) name the metal, (2) place the charge of the metal using roman numerals in brackets, and (3) name the non-metal using the ide ending. Name the following binary ionic compounds. These examples are using elements that all have more than one possible charge for the metal ion. Formula Non-Metal Ion with Charge Find Charge of Metal PbCl 2 Cl -1 Pb = +2 Pb -1-1 = 0 (so, Pb has +2 charge) Cu 2 S S -2 Cu = +1 Cu + Cu -2 = 0 (so, Cu has +1 charge) Name (use roman numeral for charge!) Lead (II) chloride Copper (I) sulfide SnO CoF 3 C. Ternary Ionic Compounds USING POLYATOMIC IONS! Finally, we need to learn how to name and write compounds that have polyatomic ions as part of the formula. Luckily for us, this is not much different than what we ve already learned! By the way, these are called TERNARY ionic compounds because they have three or more elements. With formula writing, the process is the same as it was with binary ionic compounds the only difference is that if you need more than one of a polyatomic ion, we use parentheses before we put the final subscript. Find the final formula for each of the following compounds. Notice parentheses were used when more than one polyatomic ion was needed! Compound Ions Make Charges Cancel! Final Formula Aluminum nitrate Al = 0 and NO 3 (need 1 Al +3 and 3 NO -1 3 ) Ammonium phosphate NH = 0 4 and PO 4 (need 3 NH +1 4 and 1 PO -3 4 ) Al(NO 3 ) 3 (NH 4 ) 3 PO 4 Calcium hydroxide Copper (II) sulfate Zinc chlorate

5 Naming Flowchart to help with Ionic Compound naming: Metal + nonmetal NH nonmetal Ionic Com pound Metal + poly ion NH poly ion NOTICE HOW IMPORTANT SPELLING IS!!!!! Ammonium Chloride: NH 4 Cl 1. Name metal or ammonium 2. Name non-m etal with "-ide" ending 1. Name metal or ammonium 2. Name polyatomic ion If m etal has more than one possible oxidation number, show using rom an numerals (Group 3-15 metals, except Al +3, Zn +2, Ag +1, & Cd +2 ) Ammonium Chlorate: NH 4 ClO 3 Ammonium Chlorite: NH 4 ClO 2 -ATE and ITE endings indicate POLYATOMIC IONS. -IDE endings indicate non-metal ions, except cyanide and hydroxide. D. Ionic Compounds that are HYDRATES Hydrates are ionic compounds that have trapped water in their crystal structure. They have different physical properties from the anhydrate form. the name. # Waters PREFIX # Waters PREFIX 1 mono- 6 hexa- 2 di- 7 hepta- 3 tri- 8 octa- 4 tetra- 9 nona- 5 penta- 10 deca- Use covalent prefixes to indicate the number of waters that are bound when writing Use a (dot) to show how many waters are bound when writing the formula. FORMULA Cu 2 SO 3 3H 2 O Na 2 SO 4 10H 2 O NAME Zinc sulfate heptahydrate Cobalt (II) fluoride tetrahydrate NAME Copper (I) sulfite trihydrate FORMULA ZnSO 4 7H 2 O Note that you need to include roman numerals because copper has more than one oxidation number!

6 A. INORGANIC Covalent Molecules COVALENT MOLECULES A binary covalent compound is composed of two different nonmetal elements. For example, a molecule of chlorine trifluoride, ClF 3 contains 1 atom of chlorine and 3 atoms of fluorine. STEPS TO NAMING: Step 1: Name the first non-metal using a prefix to indicate how many of that element was in the compound. Step 2: Name the second non-metal using a prefix and add the suffix -ide to the end of the name of the element. # ATOMS PREFIX # ATOMS PREFIX 1 mono- 6 hexa- 2 di- 7 hepta- 3 tri- 8 octa- 4 tetra- 9 nona- 5 penta- 10 deca- You will be tempted to use prefixes when naming ionics. DO NOT GIVE IN TO THE TEMPTATION! EXCEPTION: If the compound contains one atom of the element that is written first in the name, the prefix "mono-" is not used. Note: when the addition of the Greek prefix places two vowels adjacent to one another, the "o" or a at the end of the Greek prefix is usually dropped; "monooxide" would be written as "monoxide". The "i" at the end of the prefixes "di-" and "tri-" are never dropped. FORMULA CO 2 N 2 O 3 SO 3 BBr 3 NAME Carbon dioxide There is one carbon, but since it is the first element, we don t use the prefix mono. There are two oxygens, so we use the prefix di and change the ending to ide just like with binary ionics!) Si 2 Br 6 P 4 O 10

7 NAME PREFIXES FORMULA Dinitrogen pentoxide di = 2, pent = 5 N 2 O 5 Chlorine monofluoride Nitrogen trifluoride Triboron hexachloride B. ORGANIC Covalent Compounds We will be using organic compounds which contain carbon and hydrogen only, called hydrocarbons. The compounds will be of two general types straight chain and cyclic. Straight chain hydrocarbons will always fit the general formula. C n H 2n+2 and their names must be memorized (but they are very intuitive after the first four). These names end in -ane A cyclic hydrocarbon can be recognized by the fact that it will fit the general formula C n H 2n, and the same type of naming system will be used EXCEPT that the prefix cyclo will be placed in front of the name. HINT for the first 4: Mom Eats Peanut Butter Meth, Eth, Prop, But 1 meth- 6 hex- 2 eth- 7 hept- 3 prop- 8 oct- 4 but- 9 non- 5 pent- 10 dec- Butane, C 4 H 10 SUMMARY: They all end in ane! Put a prefix in front of ane to indicate carbons. If #H = (2 x #C) + 2 more, then you are done! If #H = (2 x #C), add cyclo at the beginning. Cyclobutane, C 4 H 8 Octane C 2 H 6 Cyclopropane C 10 H 20 Cyclopentane C 9 H 20 Heptane C 8 H 16

8 ACIDS We tend to place acids into their own category, as they follow their own set of rules. Acids are always aqueous solutions (aq). An example is HCl (aq) named hydrochloric acid. If the substance is a gas (such as HCl (g)), then use your ionic naming rules i.e. hydrogen chloride. 1. Naming Acids: Name the anion present in the acid. Change the suffix of the anion according the chart below Add the word acid as a last name. If the acid has sulfur or phosphorus, we add the ur and or back into the name. Ex. H 2 SO 3 sulfite sulfurous acid Formula of Acid Anion Name Acid Name H + non-metal ide Hydro ic acid H + poly ion (per-ate) Per ate Per ic acid H + poly ion (-ate) ate ic acid H + poly ion (-ite) ite ous acid H + poly ion (hypo-ite) Hypo ite Hypo ous acid I ate something icky and all nite I was nauseous. It reminded of when I took a ride on a hydraulic plane! FORMULA ANION NAME ACID NAME HNO 2 (aq) Nitrite Nitrous acid HF (aq) H 3 PO 3 (aq) HIO 4 (aq) 2. Writing Acid Formulas: Change the acid suffix to an anion suffix Write the anion formula Add enough H +1 to balance out the charge on the anion ACID NAME ANION NAME ANION FORMULA Phosphoric acid Phosphate ( ic = ate ) PO 4 3- Acetic acid ACID FORMULA Add H + to anion H 3 PO 4