Introduction to Nomenclature (section 2.5, Nelson Chemistry 11) Na O Al C S Ba Br

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1 Introduction to Nomenclature (section 2.5, Nelson Chemistry 11) Read p.89: To what do common names sometimes refer? What does the acronym IUPAC mean? Read p.90 (top): What is the valence of an element? How can it be determined? A more useful term for valence is oxidation number. It also is an indication of the number of electrons that are gained (negative) or lost (positive) when an atom forms a compound. Identify the oxidation number of the following atoms when they form compounds. Na O Al C S Ba Br In our section on nomenclature, many different types of compounds will be named. Consider all compounds as having two parts, a positive half and a negative half. For some, special naming rules may apply; most, however, will follow a set of simple, basic rules: 1. The substance with the positive oxidation (valence) number always goes first. 2. Except for ions, there should be a neutral (0) charge on the compound. The positive and negative halves can be balanced by adjusting the number of each atom, not the charges. 3. The name of the positive part rarely changes; the name of the negative part is almost always adjusted. A: Simple Binary Ionic Compounds (refer to p.90-91) What identifies a binary ionic compound? a) Naming: Naming basically involves easy steps: 1. Identify the first half (metal) and the second half (non-metal). 2. Change the ending of the non-metal to ide. 3. Don t worry about the number (how many) of each atom. Ex. MgO the metal half is: magnesium the non-metal half is: oxygen (change to oxide) Name the following compounds: a) MgCl 2 e) LiF b) NaBr f) CaF 2 c) Al 2O 3 g) GaP d) K 2 O h) Li 2 S the name of the compound is magnesium oxide

2 a) Writing the formula Like the name, the formula has two parts, a positive half and a negative half. Follow simple steps, such as in the crisscross rule (p.90). Read Sample Problems 1 and 2 (p.90-91) Write the formula for the following compounds: a) lithium oxide e) calcium bromide b) potassium sulphide f) aluminium chloride c) sodium nitride g) magnesium phosphide d) rubidium fluoride h) scandium iodide B: Multivalent Binary Compounds (refer to p.91-92) What does the term multivalent mean? How can multivalent elements be identified? What two naming systems can be used? a) Naming: the most significant task in naming a multivalent binary compound is stating which valence (oxidation number) of the metal is being used; this must be done, no matter what naming system is used. Different naming systems have different methods for identifying which oxidation number is being used. Notice that there are no multivalent values for negative oxidation numbers. Follow the same basic steps as before, then: 1. Identify which positive oxidation number was used for the metal based on the relative number of each atom in the formula (work backwards from the negative). 2. Determine how to indicate the positive oxidation number based on the naming system to be used. How is the positive oxidation number indicated in each of the following systems? a) IUPAC (Stock) - b) Classical system - ******REMEMBER: NIETHER SYSTEM INVOLVES INDICATING HOW MANY ATOMS OF EACH ELEMENT ARE PRESENT!!!!!!!!!!

3 Examine Sample Problems 3 and 4 (p.92) Name the following compounds a) CuBr e) FeO b) NiBr 2 f) CoP c) NiBr 3 g) PbO d) NbN h) PbO 2 b) Writing the formula: Writing the formula is as simple as before. The given name, in either naming system, will indicate the positive oxidation number of the multivalent metal. Notice that metals that are not multivalent do not have their oxidation number expressed. Follow the same steps as before, using the oxidation numbers indicated by the name. ******REMEMBER: NIETHER SYSTEM INVOLVES INDICATING HOW MANY ATOMS OF EACH ELEMENT ARE PRESENT!!!!!!!!!! Write the formula for the following compounds: a) iron (II) chloride e) stibnous phosphide b) copper (I) oxide f) cobaltous oxide b) stannous bromide g) cuprous chloride erric sulphide h) stannous sulphide Whether writing names or formulas, everything counts. All names must be correctly spelled; all symbols must be correctly d; a capitol and a small letter indicate two different things; stions: 11 OMIC IONS (refer to p ) ion is a molecule that has a charge. In nomenclature, it can be treated as a single unit, the difficulty is identifying the different ions. ing or writing formulae, just identify the correct ion by name or formula and use its given charge as its oxidation number. Notice e name if the polyatomic ion does not change (i.e. ate does not change to ide ), nor does the charge. Examine Sample Problems 5 and 6. Practice problem p. 96 #15 and 16

4 P R A C T I C E P R A C T I C E P R A C T I C E D. Molecular compounds (refer to p. 97) Molecular (covalent) compounds follow patterns very similar to those found in ionic compounds. However, they also bring up the question, If all compounds have two halves, which part of the covalent compound is the positive and which is the negative? When comparing the two elements in the compound, consider their electronegativity. The atom with the higher electronegativity is considered more negative than the one with the lower value. The lower value atom is considered relatively positive and is written first. As well, most non-metals have more than one positive oxidation number; they are multivalent. Most periodic tables don t show this information yet this is a very common occurrence. Two systems can be used to name covalent compounds: the Stock system (using Roman numerals) and the prefix system (using prefixes in front of each element). For example: the compound P 2 O 5 can be named as phosphorous (V) oxide (Stock system) What do the Roman numerals in a name indicate? or as diphosphorous pentoxide (prefix system) What do the prefixes in a name indicate? Write out the prefixes matching subscripts 1 to 10. What do you notice about the prefixes in the following set of examples? CO carbon monoxide CO 2 carbon dioxide SO 2 sulphur dioxide BF 3 boron trifluoride a. Naming: Just as in naming ionic compounds, identifying the oxidation number is essential if the Stock system is to be used. Work backwards from the oxidation number of the negative element. b. Writing the formula: If the Stock system was used, balance the oxidation numbers as before. If the prefix system was used, just identify from the prefixes how many atoms of each elelemtn are present.

5 Examine Sample Problem 7 Practice Problems: p. 98 #22 (right column), #23