Ch. 3: Molecules, Compounds, and Chemical Equations (Part I)

1. Ch. 3: Molecules, Compounds, and Chemical Equations (Part I) Dr. Namphol Sinkaset Chem 200: General Chemistry I

2. I. Chapter Outline • Introduction • Naming “Type I” Compounds • Naming “Type II” Compounds • Polyatomic Ions • Acid Names • Naming “Type III” Compounds • Molecular Masses

3. I. Chemical Formulas • There are three types of formulas. • molecular: gives the actual number of atoms of each element in a molecule of a compound (e.g. H2O2) • empirical: gives the relative number of atoms of each element in a compound (e.g. HO) • structural: uses lines to represent covalent bonds and shows interconnectivity

4. I. Chemical Models • Formulas lead to models which give an idea of the 3-D shape of a molecule.

5. I. Breakdown of Pure Substances

6. I. Chemical Nomenclature • Like any specialized field, chemistry has its own language. • The ability to name and recognize names of chemical entities is very important. • The naming system is LOGICAL!! • The periodic table is indispensable when you are first learning nomenclature.

7. II. Type I Compounds • Type I compounds are ionics that have a metal from Groups 1 or 2 and a nonmetal from Groups 14-17. • Examples: • NaCl = sodium chloride • MgBr2 = magnesium bromide • K2S = potassium sulfide

8. II. Type I Compounds • To get a formula from a name, remember that a compound must be neutral. • Ion charges can be found by locating the element on the periodic table. • “The charge on one becomes the subscript of the other.”

9. II. Type I Compounds • e.g. What are the formulas for sodium nitride, calcium chloride, potassium sulfide, and magnesium oxide?

10. III. Transition Metals • Transition metals are found in the “Valley,” Groups 3-12, of the periodic table. • Transition metal cations often can carry different charges, e.g. Fe2+ and Fe3+. • Thus, a name like “iron chloride” is ambiguous.

11. III. Type II Compounds • Type II compounds are ionics that have a transition metal (Groups 3-12) and a nonmetal (Groups 14-17). • Examples: • FeCl2 = iron(II) chloride • FeCl3 = iron(III) chloride

12. III. Type II Compounds • e.g. Give the correct name or formula for the compounds below. • MnO2 • copper(II) chloride • AuCl3 • molybdenum(VI) fluoride • Hg2Cl2

13. III. Type II Compounds • An archaic naming system uses common names for transition metal cations of different charge. • Higher charge given –ic suffix • Lower charge given –ous suffix • FeCl3 = ferric chloride • FeCl2 = ferrous chloride

14. III. Some Transition Metal Cations

15. IV. Additional Complications • To make naming ionic compounds harder, sometimes polyatomic ions are involved. • polyatomic ion: two or more atoms that are bonded covalently and have a net positive or negative charge

16. IV. Common Polyatomic Ions • These can be involved in either Type I or Type II compounds. • Polyatomic ions containing oxygen are called oxoanions.

17. IV. Oxoanion Families • There are families of oxoanions, and they have a systematic naming system. • Have either two- or four-member families. • e.g. NO2- and NO3- • e.g. ClO-, ClO2-, ClO3-, and ClO4-

18. IV. Two-Member Families • For a two-member family, oxoanion with fewer O atoms is given the “–ite” suffix while the one with more O atoms is given the “–ate” suffix. • e.g. NO2- = nitriteand NO3- = nitrate

19. IV. Four-Member Families • For the four-member families, the prefixes “hypo-” and “per-” are used to indicate fewer or more oxygen atoms. • e.g. the chlorine oxoanions • ClO- = hypochlorite • ClO2- = chlorite • ClO3- = chlorate • ClO4- = perchlorate

20. IV. Oxoanion Naming Summary

21. IV. Naming Practice • e.g. Give names or formulas for the following compounds. • Na2CO3 • magnesium hydroxide • potassium nitrate • CoPO4 • nickel(II) sulfate • NaClO2

22. V. Acids • Acids are special ionic compounds that have H+ as the cation. • There are two categories of acids that have different naming rules. • Binary acids • Oxoacids

23. V. Naming Binary Acids • Binary acids are comprised of H+ and a nonmetal anion. • HCl = hydrochloric acid • HBr = hydrobromic acid • H2Se = hydroselenic acid • HI = hydroiodic acid • So what’s the naming rule?

24. Set 1 HNO3 = nitric acid H2SO4 = sulfuric acid HClO3 = chloric acid HClO4 = perchloric acid H2CO3 = carbonic acid H3PO4 = phosphoric acid Set 2 HNO2 = nitrous acid HClO2 = chlorous acid HClO = hypochlorous acid H2SO3 = sulfurous acid V. Naming Oxoacids Oxoacids are comprised of H+ and an oxoanion. So what’s the naming rule?

25. VI. Type III Compounds • Type III compounds are covalent (nonmetal bonded to nonmetal). • Naming rules: • Element w/ lower group # is named 1st using the normal element name EXCEPT when halogens are bonded to oxygen. • If elements are in the same group, lower element named first. • Second element is named using its root and the “-ide” suffix. • #’s of atoms indicated with Greek prefixes EXCEPT when there is only one atom of the first element.

26. VI. Greek Prefixes

27. VI. Type III Compounds • Some examples: • ClO2 = chlorine dioxide • N2O5 = dinitrogen pentoxide • S2Cl2 = disulfur dichloride • SeF6 = selenium hexafluoride

28. VI. Naming Practice • e.g. Give the correct formula or name of the compounds below. • CoCl3 • dichlorine heptaoxide • SrO • magnesium hydroxide • carbon tetrachloride • HF • sodium hydride • V2O5 • Ru(ClO4)3 • hydrosulfuric acid • H2SO4 • titanium(IV) oxide • N2F2

29. VII. Masses of Compounds • Atomic masses are readily accessible via the periodic table, e.g. H = 1.008 amu. • Molecular masses or molecular weights are calculated by adding up the masses of each atom in the compound. • Thus, molecular mass = sum of atomic masses.

30. VII. Molecular Mass of Water • The formula for water is H2O, so it is comprised of 2 H atoms and 1 O atom.

31. VII. Formula Mass • e.g. What is the formula mass of barium nitrate?