Intermolecular Forces, Liquids, and Solids

Transcription

1 New Jersey enter for Teaching and Learning Slide 1 / 90 Progressive Science Initiative This material is made freely available at and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. lick to go to website: Slide 2 / 90 Intermolecular Forces, Liquids, and Solids Slide 3 / 90 Table of ontents lick on the topic to go to that section States of Matter Properties of Gases Measuring Pressure Gas Laws Ideal Gas Law Gas ensity Partial Pressure Graham's Law of ffusion Real versus Ideal Gases

2 Slide 4 / 90 States of Matter Return to Table of ontents Slide 5 / 90 So far this year. We first explained atoms, and how to build up the periodic table from quantum numbers. Then we explained how atoms combine to form molecules: the most common way we find most atoms in nature, and learned about how atoms from molecules rearrange in chemical reactions to form new chemical compounds. Now, we're going to use intermolecular forces to combine molecules to create the common states of matter. Slide 6 / 90 Intermolecular Forces Intermolecular forces are the piece we need to add to the puzzle to explain the world around us. Without intermolecular forces, we wouldn't have tables, lakes, wall...or even our bodies. Intermolecular forces shape our world.

3 Slide 7 / 90 States of Matter While there are many states of matter, the three common states that dominate our world are gases, liquids and solids. These are the states of matter we'll be studying. We won't be discussing more exotic states such as plasma, nuclear matter, etc. Slide 8 / 90 States of Matter The 2 fundamental differences between states of matter are: the distance between particles the particles' freedom to move Slide 9 / 90 States of Matter Gas cool or increase pressure heat or decrease pressure Particles are far apart, total freedom, much of empty space, total disorder Liquid rystalline solid cool heat disorder, freedom, free to move relative to each other, close together ordered arrangement, particles are in fixed positions, close together

4 Slide 10 / 90 Solid Liquid Gas njoy this musical interlude by They Might e Giants! haracteristics of the States of Matter Slide 11 / 90 Gas SHP ssumes the shape of its container VOLUM xpands to the volume of its container Is compressible OMPRSSION Flows easily FLOW Very Rapid IFFUSION haracteristics of the States of Matter Liquid SHP ssumes the shape of the part of a container it occupies VOLUM oes not expand to the volume of the container OMPRSSION Is virtually incompressible FLOW Flows easily IFFUSION Within a liquid, slow Slide 12 / 90

5 Slide 13 / 90 haracteristics of the States of Matter Solid SHP Retains its own shape regardless of container VOLUM oes not expand to the volume of its container OMPRSSION Is virtually incompressible oes not flow FLOW Within a solid, very very slow IFFUSION Slide 14 / 90 ondensed Phases In the solid and liquid states particles are closer together, we refer to them as condensed phases. Gas Liquid cool or increase pressure cool heat heat or decrease pressure Particles are far apart, total freedom, much of empty space, total disorder rystalline solid disorder, freedom, free to move relative to each other, close together ordered arrangement, particles are in fixed positions, close together Slide 15 / 90 It fills only a portion of its container. Its molecules are in relatively rigid positions. It takes on the shape of its entire container. It is not compressible. iffusion is very slow within it. nswer 1 Which of the below is a characteristic of a gas?

6 Slide 15 (nswer) / 90 1 Which of the below is a characteristic of a gas? It fills only a portion of its container. Its molecules are in relatively rigid positions. It takes on the shape of its entire container. It is not compressible. iffusion is very slow within it. nswer [This object is a pull tab] Slide 16 / 90 2 Which of the below is a characteristic of a liquid? It fills only a portion of its container. Its molecules are in relatively rigid positions. It takes on the shape of its entire container. It is compressible. iffusion is very rapid within it. 2 Which of the below is a characteristic of a liquid? It fills only a portion of its container. Its molecules are in relatively rigid positions. It takes on the shape of its entire container. It is compressible. iffusion is very rapid within it. nswer [This object is a pull tab] nswer Slide 16 (nswer) / 90

7 Slide 17 / 90 3 Which of the below is a characteristic of a solid? It fills all of its container. Its molecules are in relatively rigid positions. It takes on the shape of its entire container. It is compressible. iffusion is very rapid within it. nswer 3 Which of the below is a characteristic of a solid? It fills all of its container. Its molecules are in relatively rigid positions. It takes on the shape of its entire container. nswer It is compressible. Slide 17 (nswer) / 90 iffusion is very rapid within it. [This object is a pull tab] Slide 18 / 90 States of Matter The state of a substance at a particular temperature and pressure depends on two opposing properties: Intermolecular Forces, which pulls them together Kinetic energy of the particles, which pulls them apart Without intermolecular forces (IMF's), all molecules would be ideal gases...there would be no liquids or solids.

8 Intermolecular Forces & oiling Points Slide 19 / 90 oiling represents a transition from a liquid to a gas. To make that transition, molecules in the liquid must break free of the intermolecular forces that bind them. Intermolecular Forces & oiling Points The kinetic energy of the molecules is proportional to the temperature: as temperature rises, so does kinetic energy. Slide 20 / 90 Water molecules overcome their intermolecular forces at 100. The boiling point refers to the temperature at which the molecules' energy overcomes the intermolecular forces binding them together. The higher the boiling point of a substance, the stronger the intermolecular forces. Intermolecular Forces H l ovalent bond (strong) H l Intermolecular attraction ( weak) The attractions between molecules, intermolecular forces, are not nearly as strong as the intramolecular attractions that hold compounds together. They are, however, strong enough to control physical properties such as boiling and melting points, vapor pressures, and viscosities. Slide 21 / 90

9 Slide 22 / 90 Intermolecular Forces There are three types of Intermolecular Forces: they are sometimes called van der Waals Forces ipole-dipole interactions Hydrogen bonding London dispersion forces (LF's) ipole-ipole Interactions dipole is a polar molecule. The interaction between any two like charges is repulsive (black) + Molecules that have permanent dipoles are attracted to each other The positive end of one is attracted to the negative end of the other and vice-versa. - + These forces are only important when the molecules are close to each other. Slide 23 / The interaction between any two opposite charges is attractive ( red) Only polar molecules will have this type of Intermolecular Force. ipole-ipole Interactions The polarity of a molecule is measured by its dipole moment, m. The more polar the molecule, the greater its dipole moment. The more polar the molecule, the higher its boiling point. That's because the attraction between the dipoles holds the molecules together, not letting them boil away. Substance Molecular Weight (amu) cetonitrile, H3N cetaldehyde, H3HO Methyl chloride, H3l imethyl ether, H3OH3 Propane, H3H2H ipole Moment u() oiling Point (k) Slide 24 / 90

10 Slide 25 / 90 H3H2H3 Molecular ipole Substance Wt. Moment H3OH3 H3H2H H3l H3HO H3OH H3N H3l H3HO H3N nswer 4 Which of the below molecules will have the highest boiling point? Slide 26 / 90 H3H2H3 H3OH3 H3l H3HO H3N Substance Molecular ipole Moment Wt. H3H2H H3OH3 H3l H3HO H3N nswer 5 Which of the below molecules will have the lowest boiling point? Slide 27 / 90 London ispersion Forces London ispersion Forces occur between all molecules. They result from the fact that electrons are in constant motion and sometimes are the same side of the molecule. When they are on one side, the molecule is polarized: one side is negative and the other is positive; the molecule acts like a dipole. δ- - δ+

11 Slide 28 / 90 London ispersion Forces That polarization creates an electric field that oppositely polarizes nearby molecules...leading to an attraction. δ- δ- δ+ - δ+ - Slide 29 / 90 London ispersion Forces While the electrons in helium repel each other, they occasionally wind up on the same side of the atom. t that instant, the helium atom is polar, with an excess of electrons on one side and a shortage on the other. e2+ e- δ- Helium atom δ+ London ispersion Forces nother helium atom nearby, has a dipole induced in it, as the electrons on the left side of the first atom repel the electrons in the second. electrostatic attraction e- e2+ 2+ e- e- Helium atom 1 Helium atom 2 London dispersion forces, or dispersion forces, are attractions between an instantaneous dipole and an induced dipole. δ- δ+ δ- δ+ Slide 30 / 90

12 Slide 31 / 90 Polarizability These forces are present in all molecules, whether they are polar or nonpolar. The tendency of an electron cloud to distort in this way is called polarizability. ecause larger molecules have more electrons, they are more polarizable. Molecules with more electrons experience stronger London ispersion Forces. Slide 32 / 90 6 Molecules with more electrons experience stronger London ispersion Forces. True nswer False 6 Molecules with more electrons experience stronger London ispersion Forces. True nswer False True [This object is a pull tab] Slide 32 (nswer) / 90

13 Slide 33 / 90 London ispersion Forces xamine the trends among the halogens and the noble gases: Number oiling Noble Halogen of Point gas electrons (K) F2 l2 r2 I He Ne r Kr Xe Number oiling of point (K) electrons the greater the number of electrons, the more polarizable the particles are, resulting in stronger London dispersion forces. Slide 34 / 90 7 Which of the following molecules will have the highest boiling point? nswer F2 l2 r2 I2 7 Which of the following molecules will have the highest boiling point? l2 r2 nswer F2 I2 [This object is a pull tab] Slide 34 (nswer) / 90

14 Slide 35 / 90 F2 l2 r2 I2 nswer 8 Which of the below molecules will have the lowest boiling point? Slide 35 (nswer) / 90 8 Which of the below molecules will have the lowest boiling point? F2 l2 nswer r2 I2 [This object is a pull tab] He Ne r Kr Xe nswer 9 Which of the below molecules will have the highest boiling point? Slide 36 / 90

15 9 Which of the below molecules will have the highest boiling point? He Ne r Kr Xe nswer Slide 36 (nswer) / 90 [This object is a pull tab] 10 Which of the below molecules will have the lowest boiling point? He Ne nswer r Kr Xe 10 Which of the below molecules will have the lowest boiling point? He Ne nswer Slide 37 / 90 r Kr Xe [This object is a pull tab] Slide 37 (nswer) / 90

16 Slide 38 / 90 Which Have a Greater ffect? ipole-ipole Interactions or ispersion Forces ipole-ipole If two polar molecules are of comparable size, dipole-dipole interactions are the dominating force. ispersion Forces If one molecule is much larger than another, dispersion forces will likely determine its physical properties. If molecules are nonpolar, dispersion forces will dominate, since all molecules experience dispersion forces. Slide 39 / 90 Hydrogen onding The graph shows the boiling points for four polar and four non-polar compounds. For the non-polar series, (H4 to SnH4 ), boiling points increase with higher number of electrons. There are stronger dispersion forces due to greater polarizability. Hydrogen onding xamine the boiling points for the four polar compounds (4,2,2 = bent) called Group 16 hydrides. For this series from H2 S through H2 Te, boiling points increase with increasing polarity as expected. Recall that greater differences in electronegativities make a bond more polar. What is going on with water? It would be expected to have the lowest P in the group, but instead has the highest boliing point. Slide 40 / 90

17 Slide 41 / 90 Hydrogen onding The dipole-dipole interactions experienced when H is bonded to N, O, or F are unusually strong. We call these interactions hydrogen bonds. Hydrogen onding Slide 42 / 90 Hydrogen bonding arises in part from the high electronegativity and small radius of nitrogen, oxygen, and fluorine. When hydrogen is bonded to one of those very electronegative elements, the hydrogen nucleus is exposed. F F lick here to watch an animation about Hydrogen onding Hydrogen onding Ice is the only solid that floats in its liquid form. If it didn't, life on arth would be very different. For instance, lakes would freeze from the bottom and fish couldn't survive winters. Hydrogen bonding creates the space in ice that explains its low density. lick here to watch an animation of the Water - Ice transition Slide 43 / 90

18 Slide 44 / 90 HF Hl Hr nswer 11 Which of the following molecules has hydrogen bonding as one of its intermolecular forces? HI ll of the above. Slide 44 (nswer) / Which of the following molecules has hydrogen bonding as one of its intermolecular forces? HF Hl Hr HI ll of the above. nswer [This object is a pull tab] Slide 45 / 90 H3F H3l Hr NO2 None of the above. nswer 12 Which of the following molecules has hydrogen bonding as one of its IM forces?

19 Slide 45 (nswer) / Which of the following molecules has hydrogen bonding as one of its IM forces? H3F H3l nswer Hr NO2 None of the above. [This object is a pull tab] Slide 46 / 90 Ion-ipole Interactions There is a fourth molecular force that will be important as we explore solutions later this year: Ion-dipole interactions are not considered a van der Waals force. The strength of these forces are what make it possible for ionic substances to dissolve in polar solvents _ nion- dipole attractions ation -dipole attractions Slide 47 / 90 Summary of Interactions Interacting molecules or ions re polar molecules involved? NO NO re ions involved? YS YS re polar molecules and ions both present? YS NO re hydrogen atoms bonded to N,O,or F atoms? NO YS ispersion ipole-dipole forces only forces Hydrogen bonding (induced dipoles) H S, H l 2 3 H2O, NH3 r, I2 van der Waals forces Ion- dipole forces Nal in H2O lick here to watch a summary of IMF Ionic bonding Nal, KI

20 Slide 48 / 90 Summary of IMF London dispersion forces ipole- dipole Hydrogenbonding medium strength IMF strongest IMF Who has it? LL molecules have this IMF. Nonpolar molecules have ONLY this IMF. Only POLR molecules Only POLR molecules with a H atom covalently bonded to N, O, or F How do you tell who has it? Molecules are nonpolar if: it is diatomic, or last VSPR number is zero Molecules are polar if: it's made of ONLY 2 different atoms, or Last VSPR number is non-zero (except 642, 523 are NONpolar) What if there is a tie within a category? Look at # of electrons Look at the dipole moment (given) omparison of weakest IMF strength See above Look at which molecule has more N-H, O-H, or F-H bonds Slide 49 / 90 PH3 H 2S Hl SiH4 None of the above. nswer 13 Which of the following molecules has London dispersion as its only IM force? PH3 H 2S Hl SiH4 None of the above. [This object is a pull tab] nswer 13 Which of the following molecules has London dispersion as its only IM force? Slide 49 (nswer) / 90

21 Slide 50 / How many of these substances will have dipoledipole interactions? (How many are polar molecules?) H 2O O2 H4 NH3 nswer Slide 50 (nswer) / How many of these substances will have dipoledipole interactions? (How many are polar molecules?) H 2O nswer O2 H4 NH3 [This object is a pull tab] Slide 51 / 90 H 2O O2 H4 NH3 nswer 15 Which of the following molecules will have the highest boiling point?

22 Slide 51 (nswer) / Which of the following molecules will have the highest boiling point? H 2O O2 nswer H4 NH3 [This object is a pull tab] Slide 52 / Of the following diatomic molecules, which has the highest boiling point? N2 r2 H2 l2 O2 nswer 16 Of the following diatomic molecules, which has the highest boiling point? r2 nswer N2 H2 l2 O2 [This object is a pull tab] Slide 52 (nswer) / 90

23 Slide 53 / Of the following diatomic molecules, which has the lowest boiling point? N2 r2 nswer H2 l2 O2 Slide 53 (nswer) / Of the following diatomic molecules, which has the lowest boiling point? nswer N2 r2 H2 l2 O2 [This object is a pull tab] Slide 54 / 90 r4 F4 l4 I4 nswer 18 Which one of the following derivatives of methane (H4) has the lowest boiling point?

24 Slide 54 (nswer) / Which one of the following derivatives of methane (H4) has the lowest boiling point? r4 F4 l4 I4 nswer [This object is a pull tab] Slide 55 / Which one of the following derivatives of methane (H4) has the highest boiling point? r4 F4 l4 I4 nswer Slide 55 (nswer) / Which one of the following derivatives of methane (H4) has the highest boiling point? r4 F4 l4 I4 nswer [This object is a pull tab]

25 Intermolecular Forces ffect Many Physical Properties Slide 56 / 90 The strength of the attractions between particles can greatly affect the properties of a substance or solution. Slide 57 / 90 Viscosity Resistance of a liquid to flow is called viscosity. It is related to the ease with which molecules can move past each other. Viscosity increases with stronger intermolecular forces and decreases with higher temperature. Substance Hexane Heptane Octane Nonane ecane Formula Viscosity ( kg/m-s) H3H2H2H2H2H3 H3H2H2H2H2H2H3 H3H2H2H2H2H2H2H3 H3H2H2H2H2H2H2H2H3 H3H2H2H2H2H2H2H2H2H x x x x x 10-3 Surface Tension Surface tension results from the net inward force experienced by the molecules on the surface of a liquid. Slide 58 / 90

26 Slide 59 / 90 Phase hanges GS Vaporization ondensation nergy of system Sublimation eposition LIQUI Melting Freezing SOLI nergy hanges ssociated with hanges of State Slide 60 / 90 hemical and physical changes are usually accompanied by changes in energy. When energy is put into the system, the process is called endothermic. When energy is released by the system, the process is called exothermic. 20 Which of the following is not a phase change? vaporization effusion melting sublimation Slide 61 / 90

27 Slide 62 / 90 oiling vs. vaporation oiling and evaporation are two ways in which a liquid can vaporize into a gas. However, there are important distinctions between these processes. oiling vaporation occurs at a specific temperature, the boiling point (.P.) occurs below the boiling point occurs throughout the entire liquid occurs only at the surface of a liquid achieved when atmospheric pressure equals vapor pressure (Patm = Pvap) Slide 63 / 90 Vapor Pressure Vapor pressure is defined as the pressure exerted by gas molecules above the surface of an enclosed liquid. () () Sample () at a lower temperature shows some vapor above the surface of the liquid. Sample () at a higher temperature shows a greater number of vapor particles, thus resulting in higher vapor pressure. Slide 64 / 90 Vapor Pressure t any temperature some molecules in a liquid have enough energy to escape. s the temperature rises, the fraction of molecules that have enough energy to escape increases.

28 Liquid - Vapor quilibrium liquid becomes gas gas becomes liquid Slide 65 / 90 s more molecules escape the liquid, the pressure they exert increases. ventually, the liquid and vapor reach a state of dynamic equilibrium: liquid molecules evaporate and vapor molecules condense at the same rate. Slide 66 / 90 Vapor Pressure urve Like any line, the curve is made up of an infinite number of points. ach point along the curve shows the temperature at which atmospheric pressure equals vapor pressure Patm = Pvap In other words, each point along the curve indicates a boiling point. The type of graph shown here is called a vapor pressure curve. Vapor Pressure urve The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure. The normal boiling point is the temperature at which its vapor pressure is 760 torr. (K 760 mm Hg = 1 atm) Slide 67 / 90

29 21 What is the normal boiling point of ethanol? Slide 68 / What is the boiling point ( in o) of diethyl ether at 200 torr? What is the boiling point of water at 300 torr? Slide 69 / Slide 70 / 90

30 Pressure ooking Slide 71 / 90 liquid will boil when its vapor pressure equals atmospheric pressure. pressure cooker works by increasing the "atmospheric" pressure inside it, so water will not boil at 100o; instead, it may be heated up to 120o before turning to steam. Raising the cooking temperature cuts cooking time drastically. Pressure ooking Slide 72 / 90 Slide 73 / 90 oiling and Pressure Recall that boiling occurs when Pvap = Patm Since atmospheric pressure is so low at high altitudes, (e.g. top of Mount verest) water will boil at a much lower temperature than in New Jersey. lick here for a video of water boiling at room temperature Patm = 33 kpa on Mt. verest Patm = kpa at sea level

31 Slide 74 / It will take longer to hard-boil an egg (cooking time only) on top of Mt. verest at sea level cooking times are equal Slide 75 / 90 Volatility Volatility is another characteristic of a liquid that is based upon the strength of its intermolecular forces. The more volatile a liquid: The more quickly it evaporates The higher its vapor pressure at a given temperature The weaker its Intermolecular Forces Slide 76 / 90 Phase iagrams Phase diagrams display the state of a substance at various pressures and temperatures and the places where equilibria exist between phases.

32 Phase iagrams Slide 77 / 90 The circled line is the liquid-vapor interface. It starts at the triple point (T), the point at which all three states are in equilibrium. Phase iagrams Slide 78 / 90 The liquid-vapor interface ends at the critical point (); above this critical temperature and critical pressure the liquid and vapor are indistinguishable from each other. Phase iagrams The circled line in the diagram below is the interface between liquid and solid. The melting point at each pressure can be found along this line. Slide 79 / 90

33 Phase iagrams Slide 80 / 90 elow the triple point the substance cannot exist in the liquid state. long the circled line the solid and gas phases are in equilibrium; the sublimation point at each pressure is along this line. Phase iagram of Water Slide 81 / 90 Note the high critical temperature and critical pressure. These are due to the strong van der Waals forces between water molecules. omparison of Two Phase iagrams For water, the slope of the solid-liquid line is negative. This means that an increase in pressure can cause this substance to melt. Water is the only substance that does this. For carbon dioxide, the slope of the solid-liquid line is positive, as it is for most other substances. This means that an increase in pressure can cause substances to freeze. Slide 82 / 90

34 Phase iagram of arbon ioxide Slide 83 / 90 arbon dioxide cannot exist in the liquid state at pressures below 5.11 atm; O2 sublimes at normal pressures. The low critical temperature and critical pressure for O2 make supercritical O2 a good solvent for extracting nonpolar substances (like caffeine). Slide 84 / 90 Solids We can think of solids as falling into two groups. rystalline, in which particles are in highly ordered arrangement. morphous, in which there is no particular order in the arrangement of particles. NT ducation Resource enter Slide 85 / 90 morphous Solids Some examples of amorphous solids are: rubber, glass, paraffin wax and cotton candy. rystalline solids include ionic compounds, metals and another group called covalent-network solids. rystalline solids are categorized by bonding type as shown on the next slide.

35 Types of onding in rystalline Solids ovalent-network Solids: iamond Slide 86 / 90 Slide 87 / 90 iamonds are an example of a covalent-network solid, in which carbon atoms are covalently bonded to four other carbon atoms. They tend to be hard and have high melting points. ovalent-network Solids: Graphite Graphite is another example of a covalent-network solid. ach carbon atom is covalently bonded to 3 others in layers of interconnected hexagonal rings. The layers are held together by weak dispersion forces. The layers slide easily across one another, so graphite is used as a lubricant as well as the "lead" in pencils. Slide 88 / 90

36 Slide 89 / 90 Metallic Solids Metals are not covalently bonded, but the attractions between atoms are too strong to be van der Waals forces. In metals, valence electrons are delocalized throughout the solid. This means that the "sea" of electrons moves freely around all the nuclei. Me Me Me Me Me Me e- eme e- Me e- e- Me e- Me ee- Me Me click here for an animation about metallic bonding Properties of Metallic Solids The delocalized nature of the electrons in metals accounts for many physical properties. For example, metals are generally: good conductors of heat and electricity malleable ductile, (i.e. may be drawn into wires) Slide 90 / 90