Dr. S. M. Condren

Chapter 3

Molecules, Ions,

and their

Compounds

Dr. S. M. Condren

Structure Determination of DNA

http://mrsec.wisc.edu/Edetc/background/DNA/index.html

Dr. S. M. Condren

DNA

Dr. S. M. Condren

NaCl, saltNaCl, saltNaCl, saltNaCl, salt

Buckyball, CBuckyball, C6060

Ethanol, CEthanol, C22HH66OO

Molecules, Ions& Their Compounds

Dr. S. M. Condren

• Formula for glycine is Formula for glycine is CC22HH55NONO22

• In one molecule there areIn one molecule there are

–2 C atoms2 C atoms

–5 H atoms5 H atoms

–1 N atom1 N atom

–2 O atoms2 O atoms

MOLECULAR FORMULAS

Dr. S. M. Condren

Some Common Molecules

Dr. S. M. Condren

ExampleHow many moles of ethyl alcohol (ethanol,

C2H6O) are in a “standard” can of beer if there are 21.3 g of C C22HH66O?O?

MM = 46.069 g/mol

#mol = (21.3 g)(1 mol/46.069 g)= 0.462 mol

Dr. S. M. Condren

ExampleHow many molecules of ethyl alcohol

(ethanol, C2H6O) are in a “standard” can of beer if there are 21.3 g of C C22HH66O?O?

MM = 46.069 g/mol

#mol = 0.462 mol# molecules = (0.462 mol)

(6.022x1023 molecules/mol)= 2.78x1023 molecules

Dr. S. M. Condren

ExampleHow many C atoms are in a “standard” can

of beer if there are 21.3 g of C C22HH66O?O?

MM = 46.069 g/mol

#mol = 0.462 mol# molecules = 2.78x1023 molecules

#C atoms = (2.78x1023 molecules)(2 C atoms/molecule C2H6O)

= 5.57x1023 C atoms

Dr. S. M. Condren

Molecular & Ionic Compounds

HemeHeme NaClNaCl

Fe

N

Dr. S. M. Condren

Lithium Fluoride

Dr. S. M. Condren

+3

-4 -1-2-3+1

+2

By losing or gaining e-, atom has same By losing or gaining e-, atom has same number of e-’s as nearest Group 8A atom.number of e-’s as nearest Group 8A atom.

Charges on Common Ions

Dr. S. M. Condren

Announcement

• Lab Safety Quiz must be completed by start of lab tomorrow with a perfect score

• You can retake as many times as necessary

• Lake Study is due on Friday

Dr. S. M. Condren

AnnouncementATTN CHEMISTRY STUDENTS: Need a

Tutor? Visit the GUTS DROP IN CENTER for FREE CHEMISTRY TUTORING! Where: 1ST FLOOR OF COLLEGE LIBRARY When: Sundays, 2pm-8pm, Mondays-Wednesdays, 2pm-6pm Just stop by and work with a tutor on homework or exam prep! No registration necessary. Detailed schedule: http://

guts.studentorg.wisc.edu/dropinsummerschedule.htm With any other questions email the GUTS Office at guts@rso.wisc.edu or visit the website: http://guts.studentorg.wisc.edu

Dr. S. M. Condren

Predicting Charges on Monatomic Ions

Dr. S. M. Condren

Ion Formation

Reaction of aluminum and bromine

Dr. S. M. Condren

Dr. S. M. Condren

Combustion Analysis

Dr. S. M. Condren

Percentage Composition

description of a compound based on the relative amounts of each element in the compound

Dr. S. M. Condren

EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?MM = 1(gaw)C + 1(gaw)H + 3(gaw)Cl

= (12.011 + 1.00797 + 3*35.453)amu

= (12.011 + 1.00797 + 106.36)amu

= 119.38amu

1(gaw)C 1(12.011)%C = ----------- = ------------ X 100 = 10.061% C

119.38 119.38

Dr. S. M. Condren

EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?MM = 1(gaw)C + 1(gaw)H + 3(gaw)Cl

= (12.011 + 1.00797 + 3*35.453)amu

= 119.38amu

1(1.00797)H%H = ---------------- X 100 = 0.84436% H 119.38

Dr. S. M. Condren

EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?MM = 1(gaw)C + 1(gaw)H + 3(gaw)Cl

= (12.011 + 1.00797 + 3*35.453)amu

= 119.38amu

3(35.453)Cl%Cl = ----------------- X 100 = 89.095% Cl

119.38

Dr. S. M. Condren

EXAMPLE: What is the percent composition of chloroform, CHCl3, a substance once used as an anesthetic?MM = 1(gaw)C + 1(gaw)H + 3(gaw)Cl

= 119.377amu

%C = 10.061% C

%H = 0.84436% H

%Cl = 89.095% Cl

Dr. S. M. Condren

Simplest (Empirical) Formula

formula describing a substance based on the smallest set of subscripts

Dr. S. M. Condren

Acetylene, C2H2, and benzene, C6H6, have the same empirical formula. Is the correct empirical formula:

C2H2

CH

C6H6

Dr. S. M. Condren

EXAMPLE: A white compound is formed when phosphorus burns in air. Analysis shows that the compound is composed of 43.7% P and 56.3% O by mass. What is the empirical formula of the compound?

Element % (%/gaw)

P

O

43.7

56.3

43.7/30.97 = 1.41

56.3/15.9994 = 3.52

Divide bySmaller

1.41/1.41

= 1.00

3.52/1.41= 2.50

Multiplyby Integer

2*1.00

2*2.50

2

5

Empirical Formula => P2O5

Dr. S. M. Condren

Never round-off these numbers

Always round-off here

Example When analyzed, an unknown compound gave these experimental results: C, 54.0%; H, 6.00%, and O, 40.0%. Four different students used these values to calculate the empirical formulas shown here. Which answer is correct? Why did some students not ge the correct answer? (a) C4H5O2 (b) C5H7O3 (c) C7H10O4 (d) C9H12O5

Dr. S. M. Condren

EXAMPLE: A sample of a brown-colored gas that is a major air pollutant is found to contain 2.34 g of N and 5.34 g of O. What is the empirical formula of the compound?

5.34%O = ----------------- X 100 = 69.5% O

2.34 + 5.34

2.34 %N = ----------------- X 100 = 30.5% N 2.34 + 5.34

Dr. S. M. Condren

EXAMPLE: A sample of a brown-colored gas that is a major air pollutant is found to contain 2.34 g of N and 5.34 g of O. What is the empirical formula of the compound?%N = 30.5% N %O = 69.5% O

Element % (%/gaw)

N 30.5 30.5/14.0067 = 2.18

O 69.5 69.5/15.9994 = 4.34

Divide by Smaller2.18/2.18 = 1.00

4.34/2.18 = 1.99

1

2

Empirical Formula => NO2

x1=

x1=

Dr. S. M. Condren

Molecular Formula

the exact proportions of the elements that are formed in a molecule

Dr. S. M. Condren

Molecular Formula from Simplest Formula

empirical formula => EF

molecular formula => MF

MF = X * EF

Dr. S. M. Condren

Molecular Formula from Simplest Formula

formula mass => FM

sum of the atomic weights represented by the formula

molar mass = MM = X * FM

Dr. S. M. Condren

Molecular Formula from Simplest Formula

first, knowing MM and FM

X = MM/FM

then

MF = X * EF

Dr. S. M. Condren

EXAMPLE: A colorless liquid used in rocket engines, whose empirical formula is NO2, has a molar mass of 92.0. What is the molecular formula?

FM = 1(gaw)N + 2(gaw)O = 46.0

MM 92.0X = ------- = -------- = 2 FM 46.0

thus MF = 2 * EF

Dr. S. M. Condren

What is the correct molecular formula for this colorless liquid rocket fuel?

2NO2

NO2

N2O4

Dr. S. M. Condren

Example: A 100.00 g sample of CuSO4.XH2O was

strongly heated to drive off the waters of hydration. After the heating, the sample weighed 63.92 g. What is the value of X? the formula of the hydrated compound?

= 2.002 mol H2O

(1 mol H2O/18.02g H2O)(36.08g H2O)#mol H2O == 36.08g water= 100.00g – 63.92g

- #g anhydrous#g hydrate#g water =

#mol CuSO4 = (63.92g CuSO4)(1 mol CuSO4/159.6 g CuSO4)

= 0.4005 mol CuSO4

X= (2.002 mol H2O/0.4005 mol CuSO4) = 5

Thus CuSO4.5H2O