Nomenclature: The ABC s of Naming Chemical Compounds

Transcription

1 Nomenclature: The ABC s of Naming Chemical Compounds

2 Table of Contents 1. Naming Ionic Compounds Type I 2. Naming Ionic Compounds Type II 3. Naming Covalent Compounds 4. Naming Polyatomic Compounds

3 Welcome to your NEW Periodic Table This periodic table identifies several aspects of the elements we already know. This IS a reference tool. This IS NOT a cheat sheet. You will only ever be allowed to use ONE of your periodic tables at a time.

4 Ionic Compounds Type I

5 Ionic Compounds Without Transition Metals Ionic compounds are formed when a metal gives up its electrons to a non-metal. Basically if the compound contains a metal, it is ionic. But there are different sets of rules for transition metals. A transition metal is an element with an atomic number of 21 to 30, 39 to 48 or 57 to 80. So for a compound with any other metal, apply these rules: 1. The metal ion's name does not change regardless of charge. 2. The non-metal's name ends in the suffix -ide. For example: AlCl 3 = aluminum chloride Na 2 S = sodium sulfide K 2 O = potassium oxide MgH 2 = magnesium hydride Notice how the little numbers (subscripts) do not affect the way we name them. In going backwards (from name to formula), we will have more fun. In such a case the total charge of the (+) and (-) ions in the compound has to be ZERO.

6 Example: What is the correct chemical formula for Calcium Phosphide? Here, we have to consider the common charges for calcium and phosphorus, which are +2 and -3, respectively. Calcium, if you recall, typically loses two electrons to get a noble gas electron arrangement, and phosphorus needs three more electrons. Ca +2 and P -3 One of each would create a sum of 2 + (-3) = -1. To get a sum of zero, we need three Ca +2 ions and two P -3 for a total of 3(2)+ 2(-3) = 0. So the answer is Ca 3 P 2. Other examples: potassium oxide : K +1 and O -2 yields K 2 O aluminum bromide: Al +3 and Br -1 yields AlBr 3.

7 Kriss-Kross Method for determining Chemical Formulas Using the Kriss-Kross Method helps us to determine the chemical formula for a chemical compound when given a written equation. For example you have been given the compound Calcium Phosphide. Below you will see an example of how to use this method to determine its formula. Step 1: Write out the ion forms of both elements. 2+ Ca P 3- Step 2: Take the absolute value of the charge and Kriss-Kross their positions to the opposite element. Ca 2 P 3 Step 3: Write the chemical equation in its reduced form. Ca 3 P 2

8 Ionic Compounds Type II

9 Ionic Compounds with Transition Metals The only difference here is that we have to specify the charge of the transition metal ion by using a Roman numeral, and keep in mind that a transition metal is an element with an atomic number of 21 to 30, 39 to 48 or 57 to 80. The reason we do this is not for the sake of nostalgia for bygone Roman numerals nor to imitate movie credits. Because transition metals can assume more than one charge, we have to specify which one is involved Example: manganese(ii) oxide contains Mn +2 and O -2. So we just need one of each and the formula becomes MnO. Copper(I) oxide is Cu 2 O. To go backwards, we need to figure out the charge of the transition metal. Roman Numeral Number I 1 II 2 III 3 IV 4 V 5 VI 6 VII 7

10 Covalent Compounds Type III

11 Naming Rules and Prefixes Step 1: Name the 1 st element with its name Step 2: Name the 2 nd element with the suffix -ide Step 3: Use the prefixes to denote the number of atoms of each element. Step 4: Do NOT use the mono prefix on the 1 st element. The only time we drop a prefix is if the mono is to appear at the beginning of the name. 1 - mono 2 - di 3 - tri 4 - tetra 5 - penta 6 - hexa 7 - hepta 8 - octa 9 - nona 10 - deca

12 Naming Examples Compound Formula: OCl 2 First Element: Oxygen Second Element: dichloride Compound Name: Oxygen Dichloride Compound Formula: PCl 5 1st Element: Phophorus 2nd Element: pentachloride Compound Name: Phosphorus pentachloride

13 Check for Understanding Name Compound Formula Use the Nomenclature rules to determine the correct names of the following compounds. CO Compound Formula Name Use the Nomenclature rules to determine the correct compound formulas of the following compounds. dinitrogen pentoxide CO 2 phosphorus trichloride CH 4 Dihydrogen monoxide

14 Polyatomic Compounds

15 Naming Polyatomic Compounds When metals are bonded to polyatomic ions, which consist of two or more atoms with one overall charge, the same rules apply, but you have to learn the names and charges of common polyatomic ions. Na 2 CO 3 = sodium carbonate. ( This is a useful chemical in purifying others; it is sometimes called washing soda) KNO 3 = potassium nitrate ( This is an ingredient of gunpowder and it is also found in fertilizer.) To go backwards: Aluminum sulfate This has Al +3 and SO 4-2. To get a sum charge of ZERO, we need two aluminum ions and three sulfates, so the formula becomes Al 2 (SO 4 ) 3. Notice that when there is more than one polyatomic group, we make use of brackets.

16 List of Polyatomic Ions While memorization of these are not required it would be a good idea to know the ones with a star next to them.

17 Review Day

18 Nomenclature Summary Use this chart to help determine the names of chemical compounds Does the compound contain a metal? YES NO Is the metal a TRANSITION METAL? Compound is COVALENT; Mono=1, Di=2, Tri=3, Tetra=4, Penta=5 YES NO Use I, II, III, IV, V to indicate the charge of the metal Don t use roman numerals; Don t use prefixes