chemistry 104 lecture 1 -- imfs

8/9/2019 Chemistry 104 Lecture 1 -- IMFs

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CHEM 104--Section 2

Prof. Mills

Chemistry Dept. Hunter College

Saturday, 8:10-12:00

Room 1321A HN, Office Hrs Th 12-1

Text: Zumdahl, 8th Edition



BlackBoard 8: Instructions on how to access the

course website on bb8 can be found at:http://bb.hunter.cuny.edu. You should check the site

regularly. It can also be used to communicate with

your classmates.

Email: this is the primary form of communication

between me and you. Be sure you are either

forwarding or checking your email.



Required Homework: We will be using Quest,

an on-line homework system hosted by theUniversity of Texas. You will be required to

complete and submit homework by the

required deadlines. Specific details about thehomework with be on the homework page.

Currently there are only 83 out of 130 enrolled.



Two homework deadlines:

1) Wednesday evening covering the material

from the prior Saturday;

2) A short preview Saturday morning before

lecture.



Grading

13, 30 min tests. Each test will have 10 questions worth 1 point each.

The maximum number of points you can earn from the tests is 100pts.

Weekly homework sets. Each homework set will be scaled to 10points. The maximum number of homework points you can get is100.

Final exam: worth 200 points. The final exam will count 50% of your

grade.

Final Exam

The final will be SUNDAY, May 23 from 1:10-3:00 pm.



Daily Schedule

Except for the first day, the daily schedule will runaccording to the following schedule:

8:10-9:00 Problem solving from the week, Q&A if

needed, lecture on new material.9:00-9:30 Exam on prior week's material (every

week except week 1)

9:45-10:30 Lecture on unit material

10:30-11:30 Problem Solving/Lecture on KeyIdeas and Difficult Areas

11:30-12:00 Clicker wrap up session



The Phases of Matter and

Intermolecular Forces



Figure 10.4: Boiling Points of Elements in

Groups 4A, 5A, 6A, and 7A



Lets build an understanding to explain the graph

1) Be sure you can describe the three states of matter. Have a mental picture of the macroscopic level and the microscopic level.

2) If we describe the molecular formula and geometry of a molecule and then

we picture just that molecule, then we are thinking about an isolate

molecule. This is more akin to which phase?



From last semester

Know the lewis structure, bonding (single, double, triple, 1.5), resonance

structures, geometry. Look at methane be able to see its geometry in

your mind. The tetrahedral geometry is the most common form for organic

compounds. Get very familiar with it now.



Methane Models

Ball and Stick Model of

Methane to Emphasize

Bonding

Space Filling Model of Methane to

Emphasize Electron Density.

Both Models

Shown Side by

Side



From last semester

Dipole moment? What is it? Another way to see molecules is as a

collection of mobile electronic charge. The net charge of a molecule is zero

but this electronic charge distribution can move around. The extent towhich the charge can move around is called the POLARIZABILITY of the

molecule.

Now heres the thing. The total negative and positive charges can be balanced

and therefore the molecule has no total charge. BUT the electronicdistribution can be unsymmetric that is one side can be more negative than

the other wide. This kind of directionality is called the dipole moment.



From last semester

Practicality: if you can point a negative end towards me and a positive end

towards you, then you have a dipole moment.

Can estimate the negative and positive ends of a molecule using

electronegativities.

+ H - F -



Which of these three molecules have a

dipole moment?

I) CH4 II) CO2 III) NH3

A) I only D) I and II

B) II only E) I and II

C) III only F) II and III



Gases Condensed PhasesConsider cooling and going fromIdeal gas Real gas Liquid Solid

Ideal gas no interactions between molecules. But in reality there are

interactions but because the molecule is moving so quickly, there is no way

for the molecules to get sticky.

Real gas the molecules are sticky called inter-molecular forces. As you

cool, the stickiness appears to increase because the molecules are slowing

down. The actual energy of the stickiness remains the same but the system

starts to feel it as the molecules move more slowly.

Liquid phase stickiness overcomes the kinetic energy of the molecules andthe molecules condense. Notice that there is a BIG density change.



Figure 10.1: Schematic Representations of

Three Sates of Matter

Key Notes: liquid and solid densities are very similar gas is way lower.

Distinguishing feature between solid and liquid is order.



Basic Fact Interlude

Melting Point Temperature at which the solid melts.

Boiling Point Temperature at which the liquid boils.

Normal melting point typically the melting point at 1 atm pressure.

Normal boiling point typically the boiling point at 1 atm pressure.



Figure 10.2: (a) Electrostatic

Interaction of Two Polar Molecules;

(b) Interaction of Many Dipoles in Condensed State



Intermolecular Interactions

Always electrostatic

Hierarchy of strengths of interactions on a per int eraction basis

Charge-charge ion interactions, NaCl, MgCl2 physical properties, solids at room

temperature, high melting points, high boiling points

Dipole Dipole interactions, or permanent dipole permanent dipole

interactions. Molecules, like HF, with a permanent dipole moment interact with

each other through the dipole-dipole mechanism.

STRONG SUBSET of DIPOLE-DIPOLE interactions hydrogen bonding. IF H is

attached to O, F, or N, then the molecule can have a dipole moment. The dipolemoment is particularly strong and the H atom is particularly small. So there can be

an interaction between the H of one molecule and the O, F, or N of the other

molecule. The two atoms can get closer together than in the d-d case and form a

stronger d-d interaction.



Figure 10.3: (a) Polar H2O Molecule; (b) H

Bonding Among H2O Molecules



Intermolecular Interactions Always electrostatic

Hierarchy of strengths of interactions on a per int eraction basis

Charge-charge ion interactions, NaCl, MgCl2 physical properties, solids at roomtemperature, high melting points, high boiling points

Dipole Dipole interactions, or permanent dipole permanet dipoole

interactions. Molecules, like HF, with a permanent dipole moment interact with

each other through the dipole-dipole mechanism.

STRONG SUBSET of DIPOLE-DIPOLE interactions hydrogen bonding. IF H is

attached to O, F, or N, then the molecule can have a dipole moment. The dipole

moment is particularly strong and the H atom is particularly small. So there can be

an interaction between the H of one molecule and the O, F, or N of the other

molecule. The two atoms can get closer together than in the d-d case and form a

stronger d-d interaction.

LDF-LDF: London dispersion forces. If the molecule has NO permanent dipole

moment, its electrons can still shift around and INDUCE a dipole moment. Kind of

a shady, shifting world. This is how O2 or N2 are liquefied.



Now explain this figure

Figure 10.4: Boiling Point



Predict Physical Properties

Predict/rationalize trends in boiling

point, vapor pressure, heats of

vaporization



Figure 10.38: Behavior of

Liquid in a Closed Container

At equilibrium (b) the gas above the

liquid exerts a pressure and this is

called the vapor pressure.

Vapor Pressure

New Concept: Equilibrium and rat es of r eactions or processes




Heat of Vaporization. (Hvap. Enthalpy r equir ed to cause the

phase transition from liquid to the gas. This is a positive

quantitative, Del H vaporization is always positive

Recall problem: Consider:

Is the reaction A) endothermic or B) exothermic?

Is the sign of (H A) negative or B) positive?

2Cl Cl2




Discussion points:

How is (Hvap affected by intermolecular forces?

Butane is a gas but can be compressed into a lighter. Whats

happening here? Make a guess at the butane boiling point.

The only type of IMFs in candle wax are LDFs. Yet candle wax is

a solid. Why?



Break



SOLIDS

Molecular IonicAtomic



Ionic Solids

NaCl(s), Mg3(PO

4)

2(s)

Which is Na+: A) green, or B) purple?

Radius chloride: 181 pm

Radius sodium ion: 102 pm

Is the melting point of an ionic solid A) high or B) low? (and why?)



Molecular Solids

Dry Ice (CO2(s)) S8 P4

Figure 10.34

Relatively low melting points

(compared to ionic compounds)



SOLIDS

Molecular IonicAtomic

Network Group 8AMetals



Figure 10.22:

(a) (b)

Structures

of Diamondand Graphite

Network

Mixed Network and LDF

Network only

Directional

bonds, very

strong



Metallic

Valence electrons can be

delocalized over entire molecule

and electrons can travel away

from original nuclei.

Cu(s)



Question

Candle wax is a hydrocarbon and has the

formula CnH2n+2 where n is a fairly large number

like 20. How best could you characterize the

solid:

1) metallic, 2) atomic network, 3) molecular, 4)

ionic, 5) atomic LDF



Question

Quartz has the empirical formula SiO2. Based on

the physical properties of quartz, do you think

the solid is most like 1) metallic, 2) network, 3)

molecular, 4) LDF?



Break



Vapor Pressure depends on T

VP of Water

T P (torr)

10 9.2

25 23.7

40 55.3

100 760.0

The T of the VP when VP = 1 atm = normal boiling point



At low temperature and

high pressure I wouldexpect the substance to

be a 1) solid, 2) liquid, 3)

gas?



Particular Features

LINES two phases in

equilibrium:

boiling points line

melting points line

sublimation line



Phase Diagram for Carbon

How many triple points on this

phase diagram?

At what minimum temperature

could carbon be vaporized?

Are diamond and vapor ever in

equilibrium?

Is diamond stable at room T?



Colligative Properties

Freezing Point Depression and Boiling Point Elevation

Use the language to drive the idea: Ethylene glycol and water may freeze at

A) -5° C; B) 0 ° C; C) 5 ° C ?

Use the language to drive the idea: Ethylene glycol and water may boil at

A) 95 ° C; B) 100 ° C; C) 105 ° C ?



How does it work?

Think about what happens at the interface of

the solid and liquid.



With Solute

Rate stays same but freezing direction rate is reduced: substance melts



Questions



At P=4 atm and T = 80C, the

phase of carbon dioxide is

a) Solidb) Liquid

c) Gas



At a temperature of 60C, carbon

dioxide

A) Needs more than 72 atm of

pressure to liquefyB) Needs more than 100 atm of

pressure to solidify

C) Cannot be liquefied at any

pressure

chemistry 104 lecture 1 -- imfs

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