Chemical Formulas: Nomenclature Rules for Ionic and Covalent Compounds

1. Section 2.3—Chemical Formulas Objective: Explain and use nomenclature rules of writing ionic and covalent chemical formulas We need to be able to read the formulas for chemicals in the antacids!

2. Binary Ionic compounds

3. Ionic Compound Recall these Definitions: Ionic bond- bond formed by attraction between + and - ions Binary Ionic Compound- compound containing two elements—one metal and one non-metal – bonded through an ionic bond. + Cation - Anion

4. Ionic Charges Think about it: If ionic bonds are the attractive force between a cation (+ charge) and an anion (- charge) AND that an ionic compound contains a metal and a nonmetal, it must also be true that the metals must be charged and the nonmetals must be charged! HOW CAN WE DETERMINE THAT CHARGE??

5. Variable Positive Charges Charges for these elements will be GIVEN by a roman numeral following the cation’s name ex. iron (III) oxide: Fe is +3

6. Writing Formulas for Binary Ionic Compounds • To write these formulas: • Write the symbol & charge of the first element (the metal, cation) • Write the symbol & charge of the second element (the non-metal, anion) • Add more of the cations and/or anions in order to have a neutral compound • Use subscripts to show how many of each type of ion is there.

7. Example #1 Sodium chloride

8. Example #1 Na+1 Cation Sodium chloride Anion Cl-1 NaCl

9. Example #1 Na+1 Cation Na+1 Cl-1 Sodium chloride +1 + -1 = 0 Anion The compound is neutral…no subscripts are needed. Cl-1 NaCl

10. Example #2 Calcium bromide

11. Example #2 Ca+2 Cation Calcium bromide Anion Br-1

12. Example #2 Ca+2 Cation Ca+2 Br-1 Calcium bromide +2 + -1 = +1 Anion Ca+2 Br-1 Br-1 Br-1 +2 + -1 + -1 = 0 CaBr2 The subscript “2” is used to show that 2 anions are needed.

13. Let’s Practice Cesium chloride Potassium oxide Aluminum sulfide Calcium bromide Example: Write the following chemical formulas

14. Let’s Practice Cesium chloride Potassium oxide Aluminum sulfide Calcium bromide CsCl K2O Al2S3 CaBr2 Example: Write the following chemical formulas

15. Shortcut Criss-cross the NUMBER of the charge to obtain the subscripts. Reduce if necessary. Example1: Al+3 S-2 Al2S3 Example 2: Ca+2 O-2  Ca2O2  CaO

16. Polyatomic Ionic Compounds

17. Polyatomic Ionic Compound - Polyatomic Anion Recall these Definitions Polyatomic Ion- a group of atoms that are bonded together and have an overall charge Polyatomic Ionic Compound- compound containing at least one polyatomic ion + Cation

18. Identifying & Naming Polyatomic Ionic • To write these formulas: • Write the symbol & charge of the cation & anion; if either is a polyatomic ion, look up its charge. • Add additional cations or anions in order to have a neutral compound (OR use the criss-cross shortcut.) • Use subscripts to show the number of ions • When using subscripts with a polyatomic ion, you MUST put the polyatomic ion in parenthesis.

19. Example #3 Sodium carbonate

20. Example #3 Na+1 Cation Sodium carbonate Polyatomic Anion CO3-2

21. Example #3 Na+1 Cation Na+ CO32- Sodium carbonate +1 + -2 = -1 Polyatomic Anion Na+ Na+ CO32- +1 + 1 + -2 = 0 CO3-2 The subscript “2” is used to show that 2 cations are needed. Na2CO3

22. Example #4 Magnesium nitrate

23. Example #4 Mg+2 Cation Magnesium nitrate Polyatomic Anion NO3-1

24. Example #4 Mg+2 Mg+2 NO3- Cation +2 + -1 = +1 Magnesium nitrate Mg+2 NO3- NO3- Polyatomic Anion +2 + -1 + -1 = 0 NO3-1 Mg(NO3)2 The subscript “2” is used to show that 2 anions are needed. Parenthesis are used to show 2 anion groups are needed.

25. Let’s Practice Sodium nitrate Calcium chlorate Aluminum sulfite Calcium hydroxide Ammonium Phosphate Example: Write the following chemical formulas

26. Let’s Practice Sodium nitrate Calcium chlorate Aluminum sulfite Calcium hydroxide Ammonium Phosphate NaNO3 Ca(ClO3)2 Al2(SO3)3 Ca(OH)2 (NH4)3PO4 Example: Write the following chemical formulas

27. Binary Covalent Compounds

28. Covalent compound Definition Covalent bond atoms share electrons Binary Covalent Compound compound made from two non-metals that share electrons Non metal Non metal

29. Identifying & Naming Binary Covalent • How we named them: • Prefixes were used to indicate the number of atoms of each element • Example: N5O pentanitrogen monoxide

30. Writing Formulas • To write these formulas: • Write the symbols of the first and second element • Translate the covalent prefixes (assume the first element is “1” if there’s no prefix) into subscripts to show number of atoms. Atoms DO NOT form charges when bonding covalently…you DO NOT need to worry about charges with this type!

31. Example #7 Dinitrogen Tetraoxide

32. Example #7 “Di-” = 2 N Dinitrogen Tetraoxide O “Tetra-” = 4 N2O4

33. Example #8 Silicon dioxide

34. Example #8 “Mono-” is not written for the first element Si Silicon dioxide O “Di-” = 2 SiO2

35. Let’s Practice Carbon monoxide Nitrogen dioxide Diphosphorus pentaoxide Example: Write the following chemical formulas

36. Let’s Practice Carbon monoxide Nitrogen dioxide Diphosphorus pentaoxide CO NO2 P2O5 Example: Write the following chemical formulas

37. Diatomic Elements • Some elements are so chemically reactive that they cannot and do not exist in nature as single atoms. • If they do not find an atom of another element to bond to, they will bond to an atom of their same kind. • The formula for these such elements ALWAYS has a “2” subscript. • These elements are: hydrogen, H2 chlorine, Cl2 • nitrogen, N2 bromine, Br2 • oxygen, O2 iodine, I2 • fluorine, F2

38. Common Names & Formulas • There are a few compounds that are known by a common name, rather than a scientific one. • H2O is known as water. • NH3 is known as ammonia. • (Note: do not confuse this with the ion ammonium, NH4+)