Chapter 7
Chemical Formulas and Chemical Compound

 

I: Introduction Chemical Names and Formulas

1. common names vs IUPAC system of naming

2. Common names for: calcium carbonate, sodium chloride and hydrogen oxide

II: Significance of a Chemical Formula

1. ionic v molecular formula

2. symbol

3. subscript

4. use of parentheses

5. significance of no subscript

III: Monatomic Ions

loss or gain of electrons

monatomic ions - definition

number gained or lost for main group elements usually determined by electron configuration and octet rule

exceptions are carbon and silicon, tin and lead

d block elements (transition elements) can form +2 and +3 (e.g. iron and chromium) or sometimes +1 and +4 ions.

vanadium and lead form ions with charges of +2, +3 and +4

Naming Compounds: flowchart

a: Naming Monatomic Ions

anions and ending -ide

cations

IV: Binary Ionic Compounds

binary compounds - definition

total positive must equal total negative

cross over method using absolute value for the charges

cations always written first then anion

check subscripts and reduce to lowest whole number ratio

eliminate charges

e.g. aluminum oxide, calcium hydroxide, aluminum sulfate

V: Naming Binary Ionic Compounds

naming system = nomenclature

combine name of cation and name of anion - if binary cpd, the name of the anion must end in -ide

name the elements as you see them

examples

Homework: 7.1

a: Stock System of Nomenclature

ion that can have more than one charge e.g. Fe or Cu or Hg

name of cation followed by Roman Numeral in parentheses followed by name of anion (use ide if binary compound)

e.g. CuCl2 is copper (II) chloride

Homework: 7.2

B: Compounds Containing Polyatomic Ions

most polyatomic ions are anions

most of these are oxyanions - definition

names of oxyanions

nitrate v nitrite

hypochlorite, chlorite, chlorate, perchlorate

named the same as binary compounds i.e. name of cation followed by name of polyatomic anion

e.g. Al2(SO4)3 is aluminum sulfate

C: Naming Binary Molecular Compounds

composed of molecules not ions as above

two different systems a) Stock system and system that uses Greek prefixes
prefixes indicate the subscript
rules for binary compounds still apply
generally, the less electronegative element is written first
table 7-3 page 212 need to know

Methodology

-compound involves two nonmetals, generally
-prefix + name for first element (no prefix if subscript is one)
-prefix + name for second element -- use ending -ide if the compound is binary
-Alternate way is to use the Stock System (use of Roman numerals to indicate the charge of the cation -- do not mix with Greek prefixes)

table 7-4 page 213

Homework: 7.3 and 7.4

D: Covalent Network Compounds

all atoms joined to other atoms by covalent bonds -- no molecules

subscripts indicate ratio just as in ionic compounds

nomenclature is same as for molecular compounds

e.g. SiC, SiO2, and Si3N4

E: Acids and Salts

-acids are molecular compounds
-formula usually begins with the element hydrogen
-acids usually either binary acids or oxyacids
-binary acid - definition
-oxyacid - definition
-all acids are solutions of the compound in water -- often have he subscript (aq) after the formula
-many of our polyatomic ions come about when an oxyacid loses its hydrogen
-table 7-5 page 214
-salt - definition
-the anion of the acid may have no hydrogen or some hydrogen from the oxyacid

Homework: 7.5

Naming Compounds: flowchart

VI: Oxidation Numbers

oxidation number (oxidation state) - definition

applies to molecular compounds

often used to indicate the charge of an ion

need to know for writing formulas, naming compounds, and balancing equations

A: Assigning Oxidation Numbers

eight rules on page 216

e.g. water
e.g. hydrogen fluoride
e.g. UF6
e.g. H2SO4
e.g. ClO31-

Homework: 7.6

B: Using Oxidation Numbers and Formulas and Names

many elements have multiple oxidation states

table 7-6 page 219

the Roman numerals in the Stock system represent the oxidation numbers of the elements

can use the stock system to replace the prefix system - a trend that is becoming more popular

table on page 219 -- prefix v stock system

Homework: 7.7

VII: Using Chemical Formulas

A: Introduction

formula indicates the elements present and the relative number of atoms or ions

use formulas to calculate formula mass, molar mass, and percentage composition by mass of a compound

B: Formula Masses

formula mass - definition

e.g. Water
e.g. sodium chloride
e.g. potassium chlorate

Homework: 7.8

C: Molar Mass

molar mass of a compound - definition

e.g. barium nitrate

Homework: 7.9

D: Molar Mass as a Conversion Factor

relates amount in moles to a mass in grams

can go from moles to number of atoms or molecules using Avogadro’s number and visa versa

can go from grams to atoms or molecules using Avogadro’s number and visa versa

e.g. page 225 Sample problem 7-9 sections a and b

Homework: 7.10

E: Percentage Composition

percentage composition - definition

e.g. Sample Problem 7-10 Cu2S

e.g. Na2CO3 . 10H2O

Homework: 7.11

Determining Chemical Formulas
Introduction

new compounds are analyzed

from percentage composition data, the empirical formula can be calculated

empirical formula - definition

Calculation of Empirical Formulas

-convert percentages given to grams -- assuming a 100 gram sample
-convert grams to moles
-make the moles the subscripts
-reduce the subscripts to lowest whole number ratio
--can be done by dividing all subscripts by the smallest subscript
--keep in mind that because of rounding and experimental error the mole ratios may not appear to be whole number ratios

e.g. Sample Problem: The percentage composition of diborane is 78.1% Boron and 21.9% hydrogen. Calculate its empirical formula.

Homework: 7.12

Calculation of Molecular Formulas

the correct formula for diborane is B2H6 since it is a molecular formula; its empirical formula is BH3 as we calculated

to calculate the molecular formula you need
-the empirical (simplest formula) or the percentage composition of the compound so you can calculate the empirical formula
-the molecular (molar) mass of the compound

when calculating the molecular formula you will use the methodology:
(molar mass of the empirical formula) times x = given molar mass

e.g. Sample problem 7-14 page 232

Homework: 7.13

end of notes

A monatomic ion is an ion formed from a single atom.

A binary compound is a compound composed of two different elements.

Oxyanions are polyatomic ions that contain oxygen.

A binary acid is an acid that consists of hydrogen and one other element.

An oxyacid is an acid that contains hydrogen, oxygen and one other element.

A salt is an ionic compound composed of a cation and the anion from an acid.

An oxidation number (oxidation state) indicates the general distribution of electrons among the bonded atoms in a molecular compound.

The formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented in its formula.

The molar mass is numerically equal to its formula mass.

Percentage composition is the percentage by mass of each element in a compound.

An empirical formula consists of the symbols for the elements combined in a compound, with subscripts showing the smallest whole number ratio of the different atoms in the compound.