CHEM 120: Introduction to Inorganic Chemistry

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CHEM 120 Introduction to Inorganic Chemistry

• Instructor Upali Siriwardane (Ph.D., Ohio State
  University)
• CTH 311, Tele 257-4941, e-mail
  upali_at_chem.latech.edu
• Office hours 1000 to 1200 Tu Th 800-900
  and 1100-1200 M,W, F

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Chapters Covered and Test dates

• Tests will be given in regular class periods 
  from  930-1045 a.m. on the following days
• September 22,     2004 (Test 1) Chapters 1 2
• October 8,         2004(Test 2)  Chapters  3,
  4
• October 20,         2004 (Test 3) Chapter  5 6
  
• November 3,        2004 (Test 4) Chapter  7 8
• November 15,      2004 (Test 5) Chapter  9 10
• November 17,      2004 MAKE-UP Comprehensive
  test (Covers all chapters
• Grading
• ( Test 1 Test 2 Test3 Test4 Test5)
  x.70 Homework quiz average x 0.30 Final
  Average
•                               5

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Chapter 6. States of Matter Gases, Liquids, and
Solids

• Describe the behavior of gases Boyle's law,
  Charles's law, combined gas law, Avogadro's law,
  the ideal gas law, and Dalton's law.
• 2. Use gas law equations to calculate conditions
  and changes in conditions of gases.
• 3. Describe the major points of the kinetic
  molecular theory of gases.
• 4. Explain the relationship between the kinetic
  molecular theory and the physical properties of
  macroscopic quantities of gases.
• 5. Describe properties of the liquid state.
• 6. Describe the processes of melting, boiling,
  evaporation, and condensation.
• 7. Describe the dipolar attractions known
  collectively as London dispersion (van der
  Waals) forces.
• 8. Describe hydrogen bonding and its relationship
  to boiling and melting
• temperatures.
• 9. Relate the properties of the various classes
  of solids (ionic, covalent,
• molecular, and metallic) to the structure of
  these solids.

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States of matter

• By changing the temperature (and pressure) all
  matter can exist as a solid, as a liquid and as a
  gas.
• There are forces of attraction (which we learn
  about later) btn cmpds that determine what
  physical state (gas, liquid, solid) we find the
  cmpd in at a given temperature.

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• Temperature gives molecules kinetic energy.
  ______ the temp the ________ the kinetic energy.
• If the strength of attractive forces btn
  molecules is much larger than the kinetic energy
  due to temp the cmpd will be a ________
• If the molecules kinetic energy due to temp is
  much greater than the attractive forces btn
  molecules the cmpd will be a _______
• If the attractive forces and the energy due to
  temp are similar the cmpd will be a _______

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Elements That Exist as Gases at 25C, 1 atm
YOU READ AND BE RESPONSIBLE FOR THIS SECTION!
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• Gas properties

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• Liquid properties

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• Solid properties
• .

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• 4. In general for the same substance density
  of a solid gt density of a liquid gt density of a
  gas
• For water densityliquid gt densitysolid (ice
  floats)
• See table 6.1

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The gaseous state

• We are going to describe a gas in terms of the
  pressure (P) it exerts, the volume (V) it
  occupies and its temperature (T).
• Pressure is a
• We live at the bottom of a sea of gas molecules
  which are constantly hitting us and exerting
  pressure on us.

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Lower Atmosphere a) Troposphere (bottom) close
to earth. b) Stratosphere most atmospheric ozone
is concentrated in a layer in the
stratosphere. Upper Atmosphere c) Mesosphere d) Th
ermosphere (top)
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• The downward force on any surface area (say 1
  in2)due to air is equal to the mass of the
  column of air above the area and is 14.7psi
  (lb/in2).
• We measure the pressure of the atmosphere with a

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• Pair PHg in the barometer tube. The downward
  pressure of the mercury in the column is balanced
  by the outside atmospheric pressure pressing down
  on the mercury in the dish.
• We define one atmosphere as the atmospheric
  pressure which

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• 1 atm
• (1 torr 1 mm Hg)
• Express 528 mm Hg in atm
• Express 2.86 atm in mm Hg and torr.

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Objectives

• 4 easily measured macroscopic properties V, T,
  P, n ( moles)
• Now we want to develop a mathematical
  relationship btn P,V,T and the no. of moles (n)
  of a gas.

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Boyles law

• Boyle (1660) did some experiments that showed as
  the pressure applied to a gas increases, the
  volume occupied by the gas decreases as long as
  the temperature and amt of gas is held
  constant.

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Plot for an inverse relationship
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• or P ??1/V and V ??1/P
• PV k1 where k1 is a proportionality constant
  that is
• PiVi k1 and PfVf k1 so
• PiVi PfVf at the same temp and no.moles
  of gas

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• Gases follow Boyles law best (PVk) at
• .
• complete Pi(atm) Pf(atm) Vi(L)
  Vf(L)
• 1.0 0.50 ?
  0.30
• 1.0 2.0 0.75
  ?
• What happens to the volume if you triple the
  pressure at constant temp and no. moles?

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Charles Law, T and V

• Charles, a hot air balloonist, (1800s)
  investigated how V and T (temperature in K) were
  related.
• He found that as the temperature of the gas
  increased, the volume occupied by the gas also
  increased as long as the pressure and amt of the
  gas were held constant.

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plot for direct relationship
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• or V ??T and V k2T where k2 is a
  proportionality constant that depends on the
• Remember to convert from oC to K

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Charles Law

• V k2T
• V/T k2
• k2 proportionality constant
• independent of identity of gas
• requires constant P and n
• Vi/Ti k2 and Vf/Tf k2 so
• Vi/Ti Vf/Tf
• excellent approximation at

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• What happens to the volume when the temp in
  Kelvin is tripled at constant P and n?

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Avogadros Law, V and n

• Avogadro found that the volume of a gas increased
  as the amt of the gas increased when the pressure
  and temp were held constant. (balloon)
• V ??n or V k3n direct relationship

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• V ? n
• V k3n
• V/n k3
• Vi/ni Vf/nf
• holds best at

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Upshot of Avogadros Law

• Equal volumes of gases under the same conditions
  of temp and pressure contain equal nos. of
  particles.
• Equal moles of all gases under the same
  conditions of temp and pressure have the same
  volume.

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The Ideal Gas Law

• Boyle V ??1/P
• Charles V ? T
• Avogadro V ??n

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• An ideal gas obeys the gas laws we have
  developed. A real gas may deviate somewhat from
  these laws. But under conditions of
  _____________________, these laws are obeyed. The
  reason for this will be discussed later.

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• STP (standard temp and pressure)
• It is found that 1 mol of a gas occupies a volume
  of
• Substituting the molar volume at STP in PVnRT

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• we get

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Molar volume

• V of one mole of gas at STP 22.4 L
• Same V regardless of identity of gas!
• but
• 22.4 L of N2
• 22.4 L of CH4(g)

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Gas densities

• d
• At STP
• 1 mol of H2 has a mass of 2.0 g so dH2
• 1 mol of O2 has a mass of 32.0 g so dO2
• 1 mol of CO has a mass of 28.0 g so dCO

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• The ideal gas law contains all the other laws.

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• The temp has to be in
• In the comparative laws (Boyles, Charles, etc)
  pressure and volume just have to be in the same
  units. n has to be in moles
• In the ideal gas law the units are as specified
  before.

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Problems

• A sample of nitrogen gas kept in a container of
  volume 2.3L and at a temp of 32oC exerts a
  pressure of 4.7 atm. Calc the no. of moles and
  the mass of gas present.

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• A balloon has a volume of 43.0L at 20oC. What is
  its volume at -5oC?
• A syringe has a volume of 10.0mL at 14.7psi. If
  the tip is blocked so that air cant escape, what
  pressure is required to decrease the volume to
  2.00mL?
• If 20.0g of N2 gas has a volume of 4.00L and a
  pressure of 6.00atm, what is its temp?

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• Which sample contains more molecules 2.0L of CO2
  at 300K and 500 mm Hg or 1.5L of N2 at 57oC and
  760 mm Hg? Which sample weighs more?
• An aerosol can has an internal pressure of
  3.75atm at 25oC. What temp is required to raise
  the pressure to 16.6atm?

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• A compressed-air tank carried by scuba divers has
  a volume of 8.0L and a pressure of 140 atm at
  20oC. What is the volume of air in the tank at
  0oC and 1.00atm pressure (STP)?
• Cyclopropane. C3H6, is used as a general
  anesthetic. If a sample of cyclopropane is stored
  in a 2.00 L container at 10.0 atm and 25.0oC is
  transferred to a 5.00 L container at 5.00 atm,
  what is its resulting temp?

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• What is the effect on a gas if you
  simultaneously
• a) halve its pressure and double its Kelvin temp
• b) double its pressure and double its Kelvin
  tempereature.

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• What volume will 818 g of sulfur hexafluoride gas
  occupy if the temperature and pressure of the gas
  are 128oC and 9.4 atm?
• At what temp will 2.00 mol He fill a 2.00 L
  container at STP?

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• 6.34 How many grams of helium must be added to a
  balloon containing 8.00 g of helium gas to double
  its volume. Assume no temp or pressure change.

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Daltons Law of Partial Pressures

• Dalton (1803) said in a mixture of gases, each
  gas exerts a pressure as if it were present alone
  in the container. The pressure each gas exerts is
  called

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Daltons Law of Partial Pressures

• For gas mixtures
• Partial Pressure pressure of an individual gas
  component in a mixture
• Daltons Law of Partial Pressure total pressure
  of a mixture of gases is the sum of the pressures
  that each gas would exert if it were present
  alone

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• The mixture of gases as well as each gas obeys
  the ideal gas law and all of the other laws.

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• The partial pressure of CH4(g) is 0.225atm and
  C2H6(g) is 0.165 atm in a mixture of the two
  gases. What is the total pressure?
• A gas mixture has three components, N2, O2 and
  He. If the total pressure of the mixture is 0.78
  atm and the partial pressure of N2 and He are
  0.40 atm and 0. 18 atm respectively, what is the
  partial pressure of the O2 in the mixture?

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Kinetic Molecular Theory of Gases

• There are several basic hypotheses that are used
  to explain the behavior of gases.
• 1.Volume occupied by gas molecules themselves is
  negligible compared to the total volume occupied
  by the gas itself. (Gas molecules are though of
  as point masses have mass but occupy no volume.)

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• 2.The molecules of a gas are in constant, rapid,
  random straight line motion (Brownian motion)
  with no attractive forces btn the the molecules.
• 3.The collisions the molecules make with
  themselves and with the walls of the container
  are elastic collisions. In other words energy is
  transferred from one molecule to another in a
  collision but the total energy of the molecules
  stays the same.

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• 4. At a given time the gas molecules have
  different speeds and different kinetic energies
  but the average kinetic energy of all the
  molecules of the gas is directly proportional to
  the Kelvin temperature(T).
• KEaverage µ T or
• KEaverage cT where c is a constant
• Note that as
• Gases that obey these assumptions are known as

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How good are these assumptions?

• Zero volume?
• No attractive forces?

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• How explain compressibility, expand, low density,
  diffusion
• KE 1/2mv2
• At the same temp, molecules with

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What are these forces?

• Back to end of chapter 4 and review polar vs
  nonpolar

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Intermolecular forces

• Now what are these intermolecular forces we
  mentioned earlier.
• Intermolecular forces are forces btn different
  molecules. Intramolecular forces are forces btn
  atoms in a bond (of the order of 200-500
  kJ)--generally much stronger than intermolecular
  forces.

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• Stronger intermolecular force, the _______ the
  boiling and melting points
• What are these forces?
• I. ion-ion forces

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• II.Dipole-dipole forces forces that operate when
  have ______ molecules. In general, the more polar
  the molecule (larger the difference in
  electronegativities), the stronger the
  forces.
• These forces (dipole-dipole) are of the order of
  5 to 20 kJ/mol. Cmpds that have these forces
  (dipole-dipole) are frequently

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Dipole-Dipole
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• III. London (dispersion) forces used to explain
  intermolecular forces in
• Electrons in molecules are constantly moving.
  
• On the average, in a nonpolar molecule the
  electrons are evenly distributed leading to an
  overall equal sharing throughout.
• But since electrons are moving, at some instance
  in time there is an unequal distribution and an

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• This instantaneous dipole induces a dipole in
  neighboring molecules, creating an interaction
  btn molecules.
• This interaction is relatively weak (0.1-5 kJ).
• London and dipole-dipole forces are known
  collectively a

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• Remember as strength of forces increase have
  higher m and b pts.
• Therefore
• and
• and
• Notice that we are comparing like species,
• But what about HF, HCl, HBr, HI and H2O, H2S,
  H2Se, H2Te and NH3, PH3, AsH3 and SbH3.

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• Explain these anomalies by a new force called
• Requirements for hydrogen bonding

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• Water forms 4 hydrogen bonds per molecule, HF and
  NH3 only one.

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• Dimethyl ether (CH3OCH3) and ethanol (C2H5OH)
  have the same formula (C2H6O) but the b pt of the
  ehter is -25oC and of the ethanol 78oC. Explain.
• Which of these form hydrogen bonds?
• CH3OH
• C2H4
• CH3NH2
• HCN
• NH4

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• In general ionic forces the strongest, then
  hydrogen bonding, dipole-dipole and lastly
  dispersion for species of similar molar mass.
• N2 (bpt -195oC) O2 (bpt -183oC)
• N2 (bpt -195oC) CO (bpt -190oC) H2O (bpt
  100oC)
• CH3F (-141.8oC) CCl4 (-23oC)
• NaCl (801oC mp)

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Liquids and vapor pressure

• Put a lid on a container filled with a liquid so
  have closed system.
• Find some of the molecules in the liquid phase
  have enough KE to escape from the surface of the
  liquid and form a vapor phase.
• At the same time some of the gas molecules in the
  vapor phase fall back into the liquid.
• evaporation
• Liquid gas
• condensation

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• At some point in time the
• Say we have reached a state of dynamic
  equilibrium.
• Pressure exerted by the vapor (gas molecules)
  above the liquid is called the equilibrium
  _________________

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• The value of the vapor pressure depends on

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The green line represents the minimum energy
required to break the intermolecular
attractions. Even at the cold temp, some
molecules can be converted.
of water
energy H2O(l) ? H2O(g)
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• Normal b pt temp at which the v.p. of the liquid
  
• Boiling pt depends on strength of intermolecular
  forces.

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• Which will have the greater vapor pressure at
  5oC? The higher b pt?
• CH3OCH3 or CH3CH2OH
• CH4 or CCl4
• I2 or Cl2

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Liquid state cont

• Compressibility increased pressure essentially
  no effect on liquids and solids--brake fluid
• Viscosity resistance to flow stronger
  intermolecular forces, greater viscosity
  viscosity decreases with increase in temp.

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Liquid state

• Surface tension measure of attractive forces at
  surface of liquid--leads to sperical shape of
  drops of liquid
• Surfactant (soaps and detergents) decrease
  surface tension--grease removal

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The solid state

• Properties virtually incompressible
• Melting point temp at which change into
  liquid--depends on strength of intermolecular
  forces

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Types of crystalline solids

• Crystalline solids regular repeating order in 3D
  structure
• Types of crystalline solids
• 1. Ionic solids

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• 2. Covalent (network )solids
• 3. Molecular solids

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• 4. Metallic solids