Naming/Writing Chemical Formulas

Transcription

1 Naming/Writing Chemical Formulas

2 Chemical formulas A molecule s chemical formula tells you the ratio of atoms of each element in the compound. 2H 2 O Superscript Hydrogen How many of the element in front of it Oxygen 1 2 Means that you have 2 water molecules

3 CFU! How many of each element if present? 1. NaC 2 H 3 O 2 Na= C= H= O= 2. Ca 3 (PO 4 ) 2 Ca= P= O= 3. 3BaCl 2 Ba= Cl=

4 STRAIGHT WITH 8! Oxidation Numbers tell you how many electrons an atom can lose (-) or gain (+) when forming a compound

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

6 Ionic Compounds Type I

7 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. A. 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 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. B. 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.

8 Example #1 What is the correct 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. Work space Ca +2 and P -3 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. If necessary! ***Lets try one where we reduce & one where we use the Carbon family

9 CFU Example Formula Name H + Cl Li + Br C + O Mg + Si Rb + P Mg + S

10 Ionic Compounds Type II

11 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 because transition metals can assume more than one charge, we have to specify which one is involved Example: Iron (II) Oxide Iron (III) Oxide Work space To go backwards, we need to figure out the charge of the transition metal. Name it by writing the metal first, its charge in roman numerals, then the non-metal with the suffix -ide

12 CFU Example Formula Name Iron (II) Sulfide Cobalt (II) Nitride Tin (IV) Oxide Manganese (II) Sulfide

13 Covalent Compounds Type III

14 Roman Numerals These are formed from non-metals that share electrons. Because there are many sharing possibilities between two non-metals, the formula cannot be guessed unless we have a naming system that reveals the number of atoms involved. Prefix Number of atoms mono 1 di 2 tri 3 tetra 4 penta 5 hexa 6 The only time we drop a prefix is if the mono is to appear at the beginning of the name.

15 Examples Work space 1. CO 2. CO 2 3. dinitrogen pentoxide 4. phosphorus trichloride

16 Polyatomic Compounds

17 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: Example: Aluminum sulfate Work space If necessary!

18 Polyatomic Ion OH -1 SO -2 4 PO -3 4 NO -1 3 CO -2 3 HCO -1 3 ClO -1 3 NH +1 4 Name hydroxide sulfate phosphate nitrate carbonate hydrogen carbonate or bicarbonate chlorate ammonium

19 CFU Example Sodium Nitrate Aluminum Phosphate *Silicon Sulfate Formula Formula NaNO 3 Na 2 SO 4 Name

20 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