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
Molecules, Ions
& Their Compounds
NaCl, salt
Ethanol, C2H6O
Buckyball, C60
Dr. S. M. Condren
MOLECULAR FORMULAS
• Formula for glycine is C2H5NO2
• In one molecule there are
–2 C atoms
–5 H atoms
–1 N atom
–2 O atoms
Dr. S. M. Condren
Some Common Molecules
Dr. S. M. Condren
Example
How many moles of ethyl alcohol (ethanol,
C2H6O) are in a “standard” can of beer if
there are 21.3 g of C2H6O?
MM = 46.069 g/mol
#mol = (21.3 g)(1 mol/46.069 g)
= 0.462 mol
Dr. S. M. Condren
Example
How many molecules of ethyl alcohol
(ethanol, C2H6O) are in a “standard” can of
beer if there are 21.3 g of C2H6O?
MM = 46.069 g/mol
#mol = 0.462 mol
# molecules = (0.462 mol)
(6.022x1023 molecules/mol)
= 2.78x1023 molecules
Dr. S. M. Condren
Example
How many C atoms are in a “standard” can
of beer if there are 21.3 g of C2H6O?
MM = 46.069 g/mol
#mol = 0.462 mol
23 molecules
=
2.78x10
# molecules
#C atoms = (2.78x1023 molecules)
(2 C atoms/molecule C2H6O)
= 5.57x1023 C atoms
Dr. S. M. Condren
Molecular & Ionic Compounds
Heme
NaCl
N
Fe
Dr. S. M. Condren
Lithium Fluoride
Dr. S. M. Condren
Charges on Common Ions
-4 -3 -2 -1
+1
+2
+3
By losing or gaining e-, atom has same
number of e-’s as nearest Group 8A atom.
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
Announcement
ATTN 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:
C 2H 2
CH
C 6H 6
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)
Divide by Multiply
Smaller by Integer
P
43.7
43.7/30.97
= 1.41
1.41/1.41
= 1.00
2*1.00
2
O
56.3
56.3/15.9994 3.52/1.41
= 2.50
= 3.52
2*2.50
5
Empirical Formula => P2O5
Dr. S. M. Condren
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
Always round-off here
Never round-off these numbers
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?
2.34
%N = ----------------- X 100 = 30.5% N
2.34 + 5.34
5.34
%O = ----------------- X 100 = 69.5% O
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)
Divide by Smaller
N
30.5 30.5/14.0067 = 2.18 2.18/2.18 = 1.00 x1= 1
O
69.5 69.5/15.9994 = 4.34 4.34/2.18 = 1.99 x1= 2
Empirical Formula => NO2
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
92.0
X = ------- = -------- = 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?
#g water = #g hydrate - #g anhydrous
= 100.00g – 63.92g
= 36.08g water
#mol H2O = (36.08g H2O) (1 mol H2O/18.02g H2O)
= 2.002 mol H2O
#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
Dr. S. M. Condren