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Home , Intermolecular force, Intramolecular force, London dispersion force

12.01 Intermolecular Forces Keeping Matter Together

Water crystal

Nature’s Forces and the Magic of Dr. Fred Omega Garces 152 Miramar College

1 and Solids and IMF 05.2015 Phases of Matter: Terminology

Energy is required for phase changes to occur.

Solid-- Triangle

2 Liquids and Solids and IMF 05.2015 Heating Cooling Curve From Ice to Steam and Vice-versa

Stage1 Stage2 Stage3 Stage4 Stage5

2.08 J 40.7 kJ g ° mol 6.01 kJ 0.43 cal

mol g ° 2.05 J 80 cal g °

g 540 cal 0.49 cal 4.184 J g ° g g °

1 cal g o

Heat Addition

What is the energy needed to take 1g H2O at 0°C to 100°C ? 80 +100+ 540 =720cal

3 Liquids and Solids and IMF 05.2015 Intermolecular Forces

At the molecular level: or matter is held together by “glue” called intermolecular forces

SOLID LIQUID GAS

Energy added (K.E. increases) 4 Liquids and Solids and IMF 05.2015 Keeping Matter together

Intramolecular Forces - Force which keeps together, i.e., bonds.

Intermolecular Forces - Attractive force between molecules. Responsible for keeping matter in solid or liquid phase.

5 Liquids and Solids and IMF 05.2015 The Forces be with You 2 Basic types of - Ion - Electrostatic attraction Covalent Bonds - Mutual sharing of electrons

4 Basic types of *

1. Ion - : Ion is attracted to polar molecule (NaCl in water) 2. dipole - dipole: Polar molecules attracted to each other. 3. dipole - induce dipole: Polar molecules attracted to nonpolar molecules. ( in water) 4. induce dipole -induce dipole (London dispersion forces, LDF) nonpolar molecules attraction for each other due to electron distortion.

* plus one 6 Liquids and Solids and IMF 05.2015 Relative Strength

Interaction Example Energy ion- ion Na+ Cl- 400 - 4000 kJ Covalent Bonds H - H 150-1100 kJ + ion-dipole (I-D) Na H2O 40-600 kJ dipole - dipole (D-D) HCl HCl 5-25 kJ

dipole - induce dipole (D-ID) H2O O2 2-10 kJ

London Dispersion (LD) N2 N2 0.05 - 40 kJ

• H-Bond (10- 40 kJ/mol

7 Liquids and Solids and IMF 05.2015 Property of Matter and IMF

IMF manifestation on the Property of matter

Boiling point – Temp. necessary to cause of liquid to equal 1 atm.

Melting point – Temperature necessary to cause solid to change to liquid.

Heats of Vaporization – Energy necessary to convert liquid to vapor

Heats of Fusion- Energy necessary to melt a solid

Specific Heat- Energy necessary to raise temperature one degree

Heat Capacity- Energy necessary to raise 1 gram substance one degree temperature

Surface tension – The force necessary to separate substances at the surface

Capillary action – The between adhesive force versus cohesive force

Viscosity – The resistance for substance to flow

Vapor pressure – The pressure substance exert in a close container.

8 Liquids and Solids and IMF 05.2015 Ion - Ion Covalent Bonds

Ion - Ion: Electrostatic attraction between Na Na+

11 p 11 p 12 n 12 n

11 p 9 p 12 n 10 n F F-

9 p 9 p 10 n 10 n NaF Bond Energy: = 910 kJ/mol

Covalent Bonds: Bond between as a result of electrons sharing. F F F2 Bond Energy: = 155 kJ/mol

9 p 9 p 9 p 9 p 10 n 10 n 10 n 10 n

9 Liquids and Solids and IMF 05.2015 Review of Polarity The Charge distribution may cancel out (nonpolar) or there may be a net distortion (polar)

Analogy:

1. No one wins: nonpolar

2. One team wins: polar

3. a) no one wins: nonpolar b) one team wins: polar c) two team wins polar

10 Liquids and Solids and IMF 05.2015 Ion - Dipole

Ion - Dipole: Charge and size dependent. Most important for larger charge and small ionic radius.

Cation Ion Enthalpy of Hydration + (pm) (KJ/mol) - δ δ

Li+ 90 -515 Na+ 116 -405 K+ 152 -321 Distance between ion center and negative pole of Rb+ 166 -296 dipole Cs+ 181 -263

11 Liquids and Solids and IMF 05.2015 Dipole - Dipole Dipole - Dipole: A permanent attractive intermolecular force resulting from the interaction of the positive end of one molecule with the negative end of another.

Occurs between identical or different polar molecules.

NonPolar Polar M(g/mol) bp (°C) M (g/mol) bp (°C)

N2 28 -196 CO 28 -192 SiH4 32 -112 PH3 34 -88 GeH4 77 -90 AsH3 78 -62 Br2 160 59 ICl 162 97

12 Liquids and Solids and IMF 05.2015 Induce dipole - induced dipole: London Dispersion Forces

London Dispersion Force

(Induce dipole-Induce dipole): Intermolecular force responsible for keeping nonpolar molecules (species) together.

Polarizability - The ease of which an e- cloud can be distorted. Larger the atomic size, the greater the number of electrons, the greater the polarizability.

Boiling Point of the and Noble B.pt (K) B.pt (K)

F2 85.1 He 4.6

Cl2 238.6 Ne 27.3

Br2 332.0 Ar 87.5

I2 457.6 Kr 120.9 Xe 166.1

13 Liquids and Solids and IMF 05.2015 Boiling point versus polarizability

Graphs for family of chemicals that are polar and nonpolar; both show a fairly smooth increase of boiling point with atomic weight (larger degree of polarizability) due to increasing London Dispersion Forces

14 Liquids and Solids and IMF 05.2015 H2O: Nature of Water

Water is a liquid at

room temperature as 100°C H2O a direct consequence of bonding between adjacent HF 0°C water molecules. H2Te NH (Most other molecules with 3 SbH3 H Se comparable molar mass are 2 HI H S 2 AsH gas at room temperature) 3 SnH4 -100°C HCl HBr PH Pure water is a 3 GeG4 liquid between 0°C SiH4

and 100°C. Temperature CH4 Molar Mass (Period)

15 Liquids and Solids and IMF 05.2015 A Special Type of Bonding H-Bonding H-Bonding: A special glue above and beyond dipole- dipole intermolecular forces.

H-bonding is a strong type of intermolecular force (bond) between hydrogen and very electronegative elements (10 - 40 kJ/mol). N-H O-H F-H also consider (Cl-H)

Biochemical structural Integrity. Water possesses H-bond: Responsible for water’s unique properties.

16 Liquids and Solids and IMF 05.2015 Biological Integrity H-bonding is responsible for the structural integrity of Biological molecules. • structures • DNA and RNA

17 Liquids and Solids and IMF 05.2015 Determining IMF at Work The IMF present for matter will depend on the identity of the chemical present. For polar chemicals, dipole-dipole interaction exist as well as LDF. Dipole-dipole is the dominant IMF for polar chemicals however. For polar chemical in which H is bonded to F, N, O and Cl then in addition to the above mentioned IMF, H- bonding, the dominant IMF, is also present. For nonpolar chemicals, then LDF is the only force present. The magnitude of the IMF depends on the polarizability (LDF), dipole moment (dipole-dipole), number of H-X (H-bonding). 18 Liquids and Solids and IMF 05.2015 Example: H-bonding Which of the following substances exhibits H-bonding? Draw the H bonds between two molecules of the substances where appropriate.

a) C2H6 e) H3CCOOH

b) CH3OH f) H3CCH2OH

c) H3CCONH2 g) H3CCOCH3

d) H3C-CF3 h) H2C=O

19 Liquids and Solids and IMF 05.2015 Example: H-bonding

Which of the following substances exhibits H-bonding? Draw the H bonds between two molecules of the substances where appropriate.

a) C2H6 e) H3CCOOH No Yes

b) CH3OH f) H3CCH2OH Yes Yes

c) H3CCONH2 g) H3CCOCH3 Yes No

d) H3C-CF3 h) H2C=O No No

20 Liquids and Solids and IMF 05.2015 Example: IMF

Determine type of IM forces

Molecule LDF Dipole- H-bonding Polar or Dipole nonpolar

C2H6 X NP

CH3OH X X X P

CH3F X X P

H3C-O-CH3 X X P

NH3 X X X P

F3C-NF3 X X P

21 Liquids and Solids and IMF 05.2015 Example

Identify the dominant intermolecular forces for each of the following substances, select the dominant IMF and select the substance with the higher boiling point in each pair;

a) MgCl2 or PCl3 b) H3CNH2 or CH3F ion-dipole dipole-dipole H-bond dipole-dipole LDF LDF dipole-dipole LDF Higher Bpt LDF Higher Bpt

c) CH3OH or CH3CH2OH e) Hexane or cyclohexane H-bond H-bond LDF LDF dipole-dipole dipole-dipole Higher Bpt LDF LDF More surface area Higher Bpt Higher MWt.

22 Liquids and Solids and IMF 05.2015 Example Identify the dominant intermolecular forces for each of the following substances, select the dominant IMF and select the substance with the higher boiling point in each pair;

a) MgCl2 or PCl3 b) H3CNH2 or CH3F ion-ion dipole-dipole H-bond dipole-dipole ion-dipole LDF dipole-dipole LDF LDF LDF Higher Bpt Higher Bpt

c) CH3OH or CH3CH2OH e) Hexane or cyclohexane H-bond H-bond LDF LDF dipole-dipole dipole-dipole More surface area LDF LDF (More polariable) Higher Bpt Higher MWt. Higher BPt

23 Liquids and Solids and IMF 05.2015 Summary of Nature’s Forces

Bonding forces are relatively strong because they involve larger charges that are closer together. Ionic (400-4000 kJ/mol) Covalent (150-1100 kJ/mol)

Intermolecular forces are relatively weak because they typically involve smaller charges that are farther apart. H-bond (10-40 kJ/ mol) LDF (0.05 - 40 kJ/mol)

24 Liquids and Solids and IMF 05.2015 Overview: Recognizing Intermolecular Forces (IMF) Flowchart for recognizing the major types of intermolecular forces. London dispersion forces occur in all instances. The strength of other forces generally increases proceeding from left to right

25 Liquids and Solids and IMF 05.2015 IMF and Matter

Three States of Matter Solid - liquid - gas Intramolecular Forces Ionic Bonds & Covalent Bonds Intermolecular Forces Ion-Dipole Dipole - Dipole ion-induced dipole dipole- induced dipole London Dispersion Forces H-Bonding Water’s Unique Property to be covered …

26 Liquids and Solids and IMF 05.2015 Physical Properties of Matter

Properties:

Density(solid) – Mass of substance for the volume it occupies

Surface tension – The force necessary to separate substances at the surface

Capillary action – The interaction between adhesive force versus cohesive force

Specific Heat- Energy necessary to raise temperature

Heats of Fusion- Energy necessary to melt a solid

Heats of Vaporization – Energy necessary to convert liquid to vapor

Viscosity – The resistance for substance to flow

Boiling point – Temp. necessary to cause vapor pressure of liquid to equal 1 atm.

Melting point – Temperature necessary to cause solid to change to liquid.

Vapor pressure – The pressure substance exert in a close container.

27 Liquids and Solids and IMF 05.2015 IMF and Water’s Unique Property

Properties: Comparison with Other Importance in physical and Property substances Biological Environment Density(solid) - low density

Prevents rapid temperature Surface tension - bugs walking on Specific heat Highest of all liquids and changes; heat transfer by water solids except NH (=4.18 J/g•K) 3 movement is very large; tends to water maintain body temperature

Heat of fusion Highest except for NH3 Thermostatic effect at freezing Capillary action - method of which (=333 J/g) point due to absorption or release trees drink of heat

Specific Heat-highest among all Heat of vaporization Highest of all substances Important in heat and water liquids and solids (=2250 J/g) transfer within the atmosphere

Surface tension Highest of all liquids Important in the physiology of Viscosity - high viscosity 9 (=7.2•10 N/m) cells; controls certain surface phenomena and the behavior and Boiling point / melting point - higher Conduction of heat Highest of all liquids formation of drops than expected: Heat of fusion/

Vaporization Viscosity Less than most liquids at Flows readily to equalize pressure (=10-2 N•s/m2) comparable temperature Vapor pressure - low vapor pressure

Dielectric constant Less of all liquids except Able to keep ions separate in (=80 at 20°C) H2O2 and HCN solution

28 Liquids and Solids and IMF 05.2015 Water: Universal

Water, (CCl4) and . A) Water (a polar molecule)

and CCl4 (a nonpolar molecule) are immiscible, with the more dense water

layer found on top of the nonpolar CCl4 layer. A small amount of iodine is added in water to give a brown solution (top) - although only a small amount of iodine is dissolved in water. B) The mixture in A is then stirred.

The nonpolar molecule I2 is more

soluble in nonpolar CCl4 as indicated by the the dark color of the I2 in the

CCl4 layer.

H-bonding network between water molecules.

29 Liquids and Solids and IMF 05.2015 H2O: Density •Water has a higher density than most material as a result most insoluble material floats.

•The density of water increases slightly with increasing temperature between 0°C and 3.98 °C, where it reaches its maximum value.

•For a great majority of substances, the solid state is more dense than the liquid. The fact that water shows the reverse behavior means that lakes freeze from the top down, not the bottom up. This topsy-turvy behavior is convenient for aqueous plants, fish, and ice skaters. This same property has dangerous consequence for living cells. When living tissue freeze (frostbite) the ice crystals expands the cells and eventually rupture the cell.

30 Liquids and Solids and IMF 05.2015 H2O: Surface tension • Water has a high surface tension. –The tendency for liquids to maintain a minimum surface area is most clearly seen in the formation of spherical drops in a rain showers. This is due to the forces experience at the surface to that in the interior. In the interior each and every molecule is surrounded by other molecules; therefore, the intermolecular attractions extend in every direction equally. Not so on the surface. A liquid molecule at the surface is attracted more to other liquid molecules beneath it rather than to the gas molecules above it Therefore, there is a preferential pull toward the center of the liquid. This pull called the surface tension, crowds the molecules on the surface, thereby establishing a layer that is tough to penetrate.

Molecules at surface is attracted only to molecules below and besides. The unevenness of attraction causes surface to contract making it act like a skin.

Molecules in the interior is attracted by surrounding molecules. 31 Liquids and Solids and IMF 05.2015 H2O: Capillary action How do plants drink water?

Polar liquids typically spontaneously rise up a narrow tube. Two different types of forces are responsible for this property: Cohesive forces, the intermolecular forces within the molecules in the liquid; Adhesive forces, the attraction between the liquid molecules and the container (stem). The cohesive force results in surface tension where as adhesive force occur when a container (cellulose of stem) contains many oxygen atoms (hydrophilic components) in which the partial negative charges of the oxygen are attractive to the positive end of water (the hydrogen) to form hydrogen bonding.

For Water: FAdhesive > F Cohesive

For Mercury: FCohesive > F Adhesive

32 Liquids and Solids and IMF 05.2015 H2O: Heat Capacity

Water absorbs large amounts of heat without the temperature changing. This is due to energy going into the breaking down of H-bonding before going into molecule kinetic energy.

Heat capacity of water is 10 times greater than Cu or Fe.

The heat capacity of water accounts for the moderate climate for communities near oceans or lakes. The temperature of the earth is 59°F (15°C) compared to the moon (-387°F to +253°F, 225°F avg) or Mars (-220°F to +70°F, -81°F average ) temperature which are very extreme.

33 Liquids and Solids and IMF 05.2015 Planet without Water Imagine an Earth Without Water

Liquid water has an unusually high specific heat capacity of nearly 4.2 J/g•K, about six times that of rock (~0.7 J/g•K). If the Earth were devoid of oceans, the Sun’s energy would heat a planet composed of rock. It would take only 0.7 J ( or 0.17 cal) of energy to increase the temperature of each gram of rock by 1-degree. Daytime temperatures would soar easily into the several hundred °C. Because we have water on the Earth surface, the average temperature on Earth is 59°C. The oceans also limit the temperature drop when the Sun sets, because the energy absorbed during the day is released at night. If the Earth had a rocky surface, temperatures would be frigid every night.

34 Liquids and Solids and IMF 05.2015 H2O: Heat of Vaporization Water has the highest heat of vaporization, consequently it has a very large cooling effect during the evaporation process. Evaporating water molecules removes a considerable amount of energy.

35 Liquids and Solids and IMF 05.2015 Vapor Pressure Evaporation occurs when molecules have sufficient energy to escape the interface of a liquid substance.

Vapor Pressure - The pressure exerted by the liquid’s vapor at equilibrium.

Normal Boiling Point - The temperature at which the vapor pressure of a liquid equals the atmospheric pressure.

36 Liquids and Solids and IMF 05.2015 Phase Diagram (Revisited)

Heating - Cooling Curves and their relation to the Phase Diagram

37 Liquids and Solids and IMF 05.2015 Summary

IMF is the phenomena responsible for the phases of matter.

Water has all three IMF; LDF, DD and H-Bond. These forces makes water a special molecule. It has stronger IMF than other molecules of the same size. This manifest itself in water having properties mentioned.

38 Liquids and Solids and IMF 05.2015