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

I. Chapter Outline I.Introduction II.Naming “Type I” Compounds III.Naming “Type II” Compounds IV.Polyatomic Ions V.Acid Names VI.Naming “Type III” Compounds VII.Molecular Masses

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. H 2 O 2 )  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

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

I. Breakdown of Pure Substances

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.

II. Type I Compounds Type I compounds are ionics that have a metal from Groups 1 or 2 and a nonmetal from Groups Examples:  NaCl = sodium chloride  MgBr 2 = magnesium bromide  K 2 S = potassium sulfide

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.”

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

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. Fe 2+ and Fe 3+. Thus, a name like “iron chloride” is ambiguous.

III. Type II Compounds Type II compounds are ionics that have a transition metal (Groups 3-12) and a nonmetal (Groups 14-17). Examples:  FeCl 2 = iron(II) chloride  FeCl 3 = iron(III) chloride

III. Type II Compounds e.g. Give the correct name or formula for the compounds below. a)MnO 2 b)copper(II) chloride c)AuCl 3 d)molybdenum(VI) fluoride e)Hg 2 Cl 2

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 FeCl 3 = ferric chloride FeCl 2 = ferrous chloride

III. Some Transition Metal Cations

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

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

IV. Oxoanion Families There are families of oxoanions, and they have a systematic naming system. Have either two- or four-member families.  e.g. NO 2 - and NO 3 -  e.g. ClO -, ClO 2 -, ClO 3 -, and ClO 4 -

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. NO 2 - = nitrite and NO 3 - = nitrate

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  ClO 2 - = chlorite  ClO 3 - = chlorate  ClO 4 - = perchlorate

IV. Oxoanion Naming Summary

IV. Naming Practice e.g. Give names or formulas for the following compounds. a)Na 2 CO 3 b)magnesium hydroxide c)potassium nitrate d)CoPO 4 e)nickel(II) sulfate f)NaClO 2

V. Acids Acids are special ionic compounds that have H + as the cation. There are two categories of acids that have different naming rules. 1)Binary acids 2)Oxoacids

V. Naming Binary Acids Binary acids are comprised of H + and a nonmetal anion.  HCl = hydrochloric acid  HBr = hydrobromic acid  H 2 Se = hydroselenic acid  HI = hydroiodic acid So what’s the naming rule?

V. Naming Oxoacids Set 1  HNO 3 = nitric acid  H 2 SO 4 = sulfuric acid  HClO 3 = chloric acid  HClO 4 = perchloric acid  H 2 CO 3 = carbonic acid  H 3 PO 4 = phosphoric acid Set 2  HNO 2 = nitrous acid  HClO 2 = chlorous acid  HClO = hypochlorous acid  H 2 SO 3 = sulfurous acid Oxoacids are comprised of H + and an oxoanion. So what’s the naming rule?

VI. Type III Compounds Type III compounds are covalent (nonmetal bonded to nonmetal). Naming rules: 1)Element w/ lower group # is named 1 st using the normal element name EXCEPT when halogens are bonded to oxygen. 2)If elements are in the same group, lower element named first. 3)Second element is named using its root and the “-ide” suffix. 4)#’s of atoms indicated with Greek prefixes EXCEPT when there is only one atom of the first element.

VI. Greek Prefixes

VI. Type III Compounds Some examples:  ClO 2 = chlorine dioxide  N 2 O 5 = dinitrogen pentoxide  S 2 Cl 2 = disulfur dichloride  SeF 6 = selenium hexafluoride

VI. Naming Practice e.g. Give the correct formula or name of the compounds below. a)CoCl 3 b)dichlorine heptaoxide c)SrO d)magnesium hydroxide e)carbon tetrachloride f)HF g)sodium hydride h)V 2 O 5 i)Ru(ClO 4 ) 3 j)hydrosulfuric acid k)H 2 SO 4 l)titanium(IV) oxide m)N 2 F 2

VII. Masses of Compounds Atomic masses are readily accessible via the periodic table, e.g. H = 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.

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

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