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Liquids, Solids, and Intermolecular Forces

Liquids, Solids, and Intermolecular Forces
Liquids, Solids, and Intermolecular Forces www.ThesisScientist.comInteractions Between Molecules • Many of the phenomena we observe are related to interactions between molecules that do not involve a chemical reaction, such as taste, smell at the receptor sites in our tongue and nose, fleeting in nature. www.ThesisScientist.comInteractions Between Molecules • Important to scientists are the physical properties of solids, liquids and gas: How can water exists in three states on this planet Why are there solids What holds a liquid together Why are gasses not liquids Why does matter have such different melting and boiling points www.ThesisScientist.comThe Physical States of Matter • Matter can be classified as solid, liquid, or gas based on what properties it exhibits. State Shape Volume Compress Flow Solid Fixed Fixed No No Liquid Indef. Fixed No Yes Gas Indef. Indef. Yes Yes •Fixed = Keeps shape when placed in a container. •Indefinite = Takes the shape of the container. www.ThesisScientist.comStructure Determines Properties • The atoms or molecules have different structures in solids, liquids, and gases, leading to different properties. www.ThesisScientist.comProperties of the States of Matter: Gases • Low densities compared to solids and liquids. • Fluid. The material exhibits a smooth, continuous flow as it moves. • Take the shape of their container(s). • Expand to fill their container(s). • Can be compressed into a smaller volume. www.ThesisScientist.comProperties of the States of Matter: Liquids • High densities compared to gases. • Fluid.  The material exhibits a smooth, continuous flow as it moves. • Take the shape of their container(s). • Keep their volume, do not expand to fill their container(s). • Cannot be compressed into a smaller volume. www.ThesisScientist.comProperties of the States of Matter: Solids • High densities compared to gases. • Nonfluid.  They move as an entire ―block‖ rather than a smooth, continuous flow. • Keep their own shape, do not take the shape of their container(s). • Keep their own volume, do not expand to fill their container(s). • Cannot be compressed into a smaller volume. www.ThesisScientist.comThe Structure of Solids, Liquids, and Gases www.ThesisScientist.comGases • In the gas state, the particles have complete freedom from each other. • The particles are constantly flying around, bumping into each other and their container(s). • In the gas state, there is a lot of empty space between the particles. On average. www.ThesisScientist.comGases, Continued • Because there is a lot of empty space, the particles can be squeezed closer together. Therefore, gases are compressible. • Because the particles are not held in close contact and are moving freely, gases expand to fill and take the shape of their container(s), and will flow. www.ThesisScientist.comLiquids • The particles in a liquid are closely packed, but they have some ability to move around. • The close packing results in liquids being incompressible. • But the ability of the particles to move allows liquids to take the shape of their container and to flow. However, they don’t have enough freedom to escape and expand to fill the container(s). www.ThesisScientist.comSolids • The particles in a solid are packed close together and are fixed in position.  Though they are vibrating. • The close packing of the particles results in solids being incompressible. • The inability of the particles to move around results in solids retaining their shape and volume when placed in a new container, and prevents the particles from flowing. www.ThesisScientist.comSolids, Continued • Some solids have their particles arranged in an orderly geometric pattern. We call these crystalline solids. Salt and diamonds. • Other solids have particles that do not show a regular geometric pattern over a long range. We call these amorphous solids. Plastic and glass. www.ThesisScientist.comWhy Is Sugar a Solid, But Water Is a Liquid? • The state a material exists in depends on the attraction between molecules and their ability to overcome the attraction. • The attractive forces between ions or molecules depends on their structure.  The attractions are electrostatic.  They depend on shape, polarity, etc. • The ability of the molecules to overcome the attraction depends on the amount of kinetic energy they possess. www.ThesisScientist.comProperties and Attractive Forces Relative strength of attractive Phase Density Shape Volume forces Gas Low Indefinite Indefinite Weakest Liquid High Indefinite Definite Moderate Solid High Definite Definite Strongest www.ThesisScientist.comPhase Changes: Melting • Generally, we convert a material in the solid state into a liquid by heating it. • Adding heat energy increases the amount of kinetic energy of the molecules in the solid. • Eventually, they acquire enough energy to partially overcome the attractive forces holding them in place. • This allows the molecules enough extra freedom to move around a little and rotate. www.ThesisScientist.comPhase Changes: Boiling • Generally, we convert a material in the liquid state into a gas by heating it. • Adding heat energy increases the amount of kinetic energy of the molecules in the liquid. • Eventually, they acquire enough energy to completely overcome the attractive forces holding them together. • This allows the molecules complete freedom to move around and rotate. www.ThesisScientist.comProperties of Liquids: Surface Tension • Liquids tend to minimize their surface—a phenomenon we call surface tension. • This tendency causes liquids to have a surface that resists penetration. • The stronger the attractive force between the molecules, the larger the surface tension. www.ThesisScientist.comSurface Tension • Molecules in the interior of a liquid experience attractions to surrounding molecules in all directions. • However, molecules on the surface experience an imbalance in attractions, effectively pulling them in. • To minimize this imbalance and maximize attraction, liquids try to minimize the number of molecules on the exposed surface by minimizing their surface area. • Stronger attractive forces between the molecules = larger surface tension. www.ThesisScientist.comProperties of Liquids: Viscosity • Some liquids flow more easily than others. • The resistance of a liquid’s flow is called viscosity. • The stronger the attractive forces between the molecules, the more viscous the liquid is. • Also, the less round the molecule’s shape, the larger the liquid’s viscosity.  Some liquids are more viscous because their molecules are long and get tangled in each other, causing them to resist flowing. www.ThesisScientist.comEvaporation • The evaporation happens at the surface. • Molecules on the surface experience a smaller net attractive force than molecules in the interior. • All the surface molecules do not escape at once, only the ones with sufficient kinetic energy to overcome the attractions will www.ThesisScientist.com escape.Escaping the Surface • The average kinetic energy is directly proportional to the Kelvin temperature. • Not all molecules in the sample have the same amount of kinetic energy. • Those molecules on the surface that have enough kinetic energy will escape.  Raising the temperature increases the number of molecules with sufficient energy to escape. www.ThesisScientist.comEscaping the Surface, Continued • Since the higher energy molecules from the liquid are leaving, the total kinetic energy of the liquid decreases, and the liquid cools. • The remaining molecules redistribute their energies, generating more high energy molecules. • The result is that the liquid continues to evaporate . www.ThesisScientist.comFactors Effecting the Rate of Evaporation • Liquids that evaporate quickly are called volatile liquids, while those that do not are called nonvolatile. • Increasing the surface area increases the rate of evaporation.  More surface molecules. • Increasing the temperature increases the rate of evaporation.  Raises the average kinetic energy, resulting in more molecules that can escape. • Weaker attractive forces between the molecules = faster rate of evaporation. www.ThesisScientist.comReconnecting with the Surface • When a liquid evaporates in a closed container, the vapor molecules are trapped. • The vapor molecules may eventually bump into and stick to the surface of the container or get recaptured by the liquid. This process is called condensation. A physical change in which a gaseous form is converted to a liquid form. www.ThesisScientist.comEvaporation and Condensation Shortly, the water When water is just starts to evaporate. added to the flask Initially the rate and it is capped, all of evaporation is the water molecules much faster than rate are in the liquid. of condensation Opposite processes that Eventually, the condensation occur at the same rate in and evaporation reach the the same system are said same speed. The air in the to be in dynamic flask is now saturated with equilibrium. water vapor. www.ThesisScientist.comVapor Pressure • Once equilibrium is reached, from that time forward, the amount of vapor in the container will remain the same. As long as you don’t change the conditions. • The partial pressure exerted by the vapor is called the vapor pressure. • The vapor pressure of a liquid depends on the temperature and strength of intermolecular attractions. www.ThesisScientist.comBoiling • In an open container, as you heat a liquid the average kinetic energy of the molecules increases, giving more molecules enough energy to escape the surface.  So the rate of evaporation increases. • Eventually, the temperature is high enough for molecules in the interior of the liquid to escape. A phenomenon we call boiling. www.ThesisScientist.comBoiling Point • The temperature at which the vapor pressure of the liquid is the same as the atmospheric pressure is called the boiling point.  The normal boiling point is the temperature required for the vapor pressure of the liquid to be equal to 1 atm. • The boiling point depends on what the atmospheric pressure is.  The temperature of boiling water on the top of a mountain will be cooler than boiling water at sea level. www.ThesisScientist.comTemperature and Boiling • As you heat a liquid, its temperature increases until it reaches its boiling point. • All the energy from the heat source is being used to overcome all of the attractive forces in the liquid. www.ThesisScientist.comEnergetics of Evaporation • As it loses its high energy molecules through evaporation, the liquid cools. • Then the liquid absorbs heat from its surroundings to raise its temperature back to the same as the surroundings. • Processes in which heat flows into a system from the surroundings are said to be endothermic. • As heat flows out of the surroundings, it causes the surroundings to cool.  As alcohol evaporates off your skin, it causes your skin to cool. www.ThesisScientist.comEnergetics of Condensation • As it gains the high energy molecules through condensation, the liquid warms. • Then the liquid releases heat to its surroundings to reduce its temperature back to the same as the surroundings. • Processes in which heat flows out of a system into the surroundings are said to be exothermic. • As heat flows into the surroundings, it causes the surroundings to warm. www.ThesisScientist.comHeat of Vaporization • The amount of heat needed to vaporize one mole of a liquid is called the heat of vaporization. DH vap  It requires 40.7 kJ of heat to vaporize one mole of water at  100 °C.  Always endothermic. Number is +. DH depends on the initial temperature. vap • Since condensation is the opposite process to evaporation, the same amount of energy is transferred but in the opposite direction. DH = −DH condensation vaporization www.ThesisScientist.comHeats of Vaporization of Liquids at Their Boiling Points and at 25 °C DH at vap Normal boiling DH at vap Chemical boiling point, 25 °C, Liquid formula point, °C (kJ/mol) (kJ/mol) Water H O 100 +40.7 +44.0 2 Isopropyl C H OH 82.3 +39.9 +45.4 3 7 alcohol Acetone C H O 56.1 +29.1 +31.0 3 6 Diethyl C H O 34.5 +26.5 +27.1 4 10 ether www.ThesisScientist.comExample 12.1—Calculate the Mass of Water that Can Be Vaporized with 155 KJ of Heat at 100 °C. Given: 155 kJ Find: g H O 2 Solution Map: kJ mol H O g H O 2 2 1 mol 18.02 g 40.7 kJ 1 mol Relationships: 1 mol H O = 40.7 kJ, 1 mol = 18.02 g 2 Solution: 1 mol H O 18.02 g 2 155 kJ  68.6 g H O 2 40.7 kJ 1 mol Check: Since the given amount of heat is almost 4x the DH , the amount of water makes sense. vap www.ThesisScientist.comPractice—How Much Heat Energy, in kJ, is Required to Vaporize 87 g of Acetone, C H O, (MM 58.08) at 25 C? 3 6 (DH = 31.0 kJ/mol) vap www.ThesisScientist.comPractice—How Much Heat Energy, in kJ, Is Required to Vaporize 87 g of Acetone, C H O, (MM 58.08) at 25 C? 3 6 (DH = 31.0 kJ/mol), Continued vap Given: 87 g C H O 3 6 Find: kJ Solution Map: g C H O mol C H O kJ 3 6 3 6 1 mol 31.0 kJ 58.08 g 1 mol Relationships: 1 mol C H O = 31.0 kJ at 25 C, 1 mol = 58.08 g 3 6 Solution: 1 mol C H O 31.0 kJ 3 6 87 g C H O  46 kJ 3 6 58.08 g 1 mol C H O 3 6 Check: Since the given mass is than one mole, the answer being greater than DH makes sense. vap www.ThesisScientist.comTemperature and Melting • As you heat a solid, its temperature increases until it reaches its melting point. • Once the solid starts to melt, the temperature remains the same until it all turns to a liquid. • All the energy from the heat source is being used to overcome some of the attractive forces in the solid that hold them in place. www.ThesisScientist.comEnergetics of Melting and Freezing • When a solid melts, it absorbs heat from its surroundings, it is endothermic. • As heat flows out of the surroundings, it causes the surroundings to cool.  As heat flows out of your drink into the ice cubes (causing them to melt), the liquid gets cooler. • When a liquid freezes, it releases heat into its surroundings, it is exothermic. • As heat flows into the surroundings, it causes the surroundings to warm.  Orange growers often spray their oranges with water when a freeze is expected. Why? www.ThesisScientist.comHeat of Fusion • The amount of heat needed to melt one mole of a solid is called the heat of fusion. DH fus  Fusion is an old term for heating a substance until it melts, it is not the same as nuclear fusion. • Since freezing (crystallization) is the opposite process of melting, the amount of energy transferred is the same, but in the opposite direction. DH = -DH crystal fus • In general, DH DH because vaporization requires vap fus breaking all attractive forces. www.ThesisScientist.comHeats of Fusion of Several Substances Chemical Melting DH , fusion Liquid formula point, °C (kJ/mol) Water H O 0.00 6.02 2 Isopropyl alcohol C H OH -89.5 5.37 3 7 Acetone C H O -94.8 5.69 3 6 Diethyl ether C H O -116.3 7.27 4 10 www.ThesisScientist.comPractice—How Much Heat Energy, in kJ, is Required to Melt 87 g of Acetone, C H O, (MM 58.08)? 3 6 (DH = 5.69 kJ/mol) fus www.ThesisScientist.comPractice—How Much Heat Energy, in kJ, Is Required to Melt 87 g of Acetone, C H O, (MM 58.08)?, Continued 3 6 Given: 87 g C H O 3 6 Find: kJ Solution Map: g C H O mol C H O kJ 3 6 3 6 1 mol 5.69 kJ 58.08 g 1 mol Relationships: 1 mol C H O = 5.69 kJ at -94.8 C, 1 mol = 58.08 g 3 6 Solution: 1 mol C H O 5.69 kJ 3 6 87 g C H O  8.5 kJ 3 6 58.08 g 1 mol C H O 3 6 Check: Since the given mass is more than one mole, the answer being greater than DH makes sense. vap www.ThesisScientist.comSublimation • Sublimation is a physical change in which the solid form changes directly to the gaseous form. Without going through the liquid form. • Like melting, sublimation is endothermic. www.ThesisScientist.comIntermolecular Attractive Forces www.ThesisScientist.comEffect of the Strength of Intermolecular Attractions on Properties • The stronger the intermolecular attractions are, the more energy it takes to separate the molecules. • Substances with strong intermolecular attractions have higher boiling points, melting points, and heat of vaporization; they also have lower vapor pressures. www.ThesisScientist.comPractice—Pick the Substance in Each Pair with the Stronger Intermolecular Attractions. • • su sug gar ar o or r water water. • • water o water or r aceton acetone e. • • ice ice o or r d dry ry ice ice. www.ThesisScientist.comAttractive Forces and Properties • Like dissolves like.  Miscible = Liquids that do not separate, no matter what the proportions. 1. Ionic 2. Polar molecules dissolve in polar solvents.  Water, alcohol, CH Cl . 2 2 3. A special case of polarity: Molecules with O or N higher solubility in H O due to H-bonding with H O. 2 2 4. Nonpolar molecules dissolve in nonpolar solvents or Dispersion forces  Ligroin (hexane), toluene, CCl . 4 • If molecule has both polar and nonpolar parts, then hydrophilic-hydrophobic competition. www.ThesisScientist.comDispersion Forces • Also known as London forces or instantaneous dipoles. • Caused by distortions in the electron cloud of one molecule inducing distortion in the electron cloud on another. • Distortions in the electron cloud lead to a temporary dipole. • The temporary dipoles lead to attractions between molecules—dispersion forces. • All molecules have attractions caused by dispersion forces. www.ThesisScientist.comInstantaneous Dipoles www.ThesisScientist.comStrength of the Dispersion Force • Depends on how easily the electrons can move, or be polarized. • The more electrons and the farther they are from the nuclei, the larger the dipole that can be induced. • Strength of the dispersion force gets larger with larger molecules. www.ThesisScientist.comDispersion Force and Molar Mass Noble Gas Molar Mass Boiling Point (g/mol) (K) He 4.00 4.2 Ne 20.18 27 Ar 39.95 87 Kr 83.80 120 Xe 131.29 165 www.ThesisScientist.comPractice—The Following Are All Made of Non– Polar Molecules. Pick the Substance in Each Pair with the Highest Boiling Point. • • CH CH o or r C C H H . 4 4 3 3 8 8 • • BF BF o or r BC BCl l . 3 3 3 3 • • CO CO o or r CS CS . 2 2 2 2 www.ThesisScientist.comPermanent Dipoles • Because of the kinds of atoms that are bonded together and their relative positions in the molecule, some molecules have a permanent dipole.  Polar molecules. • The size of the molecule’s dipole is measured in debyes, D. www.ThesisScientist.comDipole-to-Dipole Attraction • Polar molecules have a permanent dipole. A + end and a – end. • The + end of one molecule will be attracted to the – end of another. www.ThesisScientist.comPolarity and Dipole-to-Dipole Attraction Molar Mass Boiling Dipole (g/mol) Point, °C size, D CH CH CH 44 -42 0 3 2 3 CH -O-CH 46 -24 1.3 3 3 CH - CH=O 44 20.2 2.7 3 41 81.6 3.9 CH -CN 3 www.ThesisScientist.comAttractive Forces Dispersion forces—All molecules. _ + + _ + _ + _ Dipole-to-dipole forces—Polar molecules. + - + - + - + - www.ThesisScientist.comIntermolecular Attraction and Properties • All molecules are attracted by dispersion forces. • Polar molecules are also attracted by dipole- dipole attractions. • Therefore, the strength of attraction is stronger between polar molecules than between nonpolar molecules of the same size. www.ThesisScientist.comPractice—Determine Which of the Following Has Dipole–Dipole Attractive Forces. (EN C= 2.5, F = 4, H = 2.1, S = 2.5) • • CS CS Nonpolar bonds = nonpolar molecule. 2 2  S C S • • CH CH F F Polar bonds and asymmetrical = polar molecule. 2 2 2 2 H C F H F • • CF CF Polar bonds and symmetrical shape = nonpolar 4 4 molecule. F C F F F www.ThesisScientist.com          Attractive Forces and Properties • Like dissolves like.  Miscible = Liquids that do not separate, no matter what the proportions. 1. Ionic 2. Polar molecules dissolve in polar solvents.  Water, alcohol, CH Cl . 2 2  Molecules with O or N higher solubility in H O due to H- 2 bonding with H O. 2 3. Nonpolar molecules dissolve in nonpolar solvents.  Ligroin (hexane), toluene, CCl . 4 • If molecule has both polar and nonpolar parts, then hydrophilic-hydrophobic competition. www.ThesisScientist.comImmiscible Liquids When liquid pentane, a nonpolar substance, is mixed with water, a polar substance, the two liquids separate because they are more attracted to their own kind of molecule than to the other. www.ThesisScientist.comHydrogen Bonding • HF, or molecules that have OH or NH groups have particularly strong intermolecular attractions.  Unusually high melting and boiling points.  Unusually high solubility in water. • This kind of attraction is called a hydrogen bond. www.ThesisScientist.comRelationship Between H-Bonding and Intermolecular Attraction 150 H O 2 100 50 HF H Te 2 0 1 2 3 4 5 NH H Se 3 2 H S 2 -50 SnH 4 -100 GeH BP, HX 4 SiH 4 BP, H2X -150 CH 4 BP, H3X -200 BP, XH4 Period www.ThesisScientist.com Boiling Point, °CProperties and H-Bonding Molar Boiling Melting Solubility mass point, point, Name Formula Structure in water (g/mol) °C °C H H Immiscible H C C H Ethane C H 30.0 -88 -172 2 6 H H H H C O H Miscible Ethanol CH O 32.0 64.7 -97.8 4 H www.ThesisScientist.comIntermolecular H-Bonding www.ThesisScientist.comHydrogen Bonding • When a very electronegative atom is bonded to hydrogen, it strongly pulls the bonding electrons toward it. • Since hydrogen has no other electrons, when it loses the electrons, the nucleus becomes deshielded. Exposing the proton. • The exposed proton acts as a very strong center of positive charge, attracting all the electron clouds from neighboring molecules. www.ThesisScientist.comH-Bonds vs. Chemical Bonds • Hydrogen bonds are not chemical bonds. • Hydrogen bonds are attractive forces between molecules. • Chemical bonds are attractive forces that make molecules. www.ThesisScientist.comAttractive Forces and Properties Molar Boiling Solubility Mass Point, in water (g/mol) °C (g/100 g H O) 2 CH CH OCH CH 3 2 2 3 74 34.6 7.5 CH CH CH CH CH 3 2 2 2 3 72 36 Insoluble CH CH CH CH OH 3 2 2 2 74 117 9 www.ThesisScientist.comExample 12.5—Which of the Following Is a Liquid at Room Temperature? (The Other Two Are Gases.) • • fo form rmal ald deh ehy yd de, e, CH CH O O. 2 2 O  30.0 30.03 3 g g/m /mol. ol C  polar polar mol mole ec cule ule  dipo dipole le– –dipo dipole le a att ttr ra ac cti tions pre ons present sent. H H  P po olar lar C C= =O O b bo on nd d & and asy asy mm mm etr etr icic. • • fl flu uo oro rom met eth hane, ane, CH CH F F. 3 3 F  34.03 34.03 g g/m /mol ol. C  pol pola ar r mo molec lecule ule  dip dipole ole– –dip dipole ole a att ttra rac cti tions ons pre present sent. H H  P po olar lar C C−F −F b bo on nd d & and as asy ymm mm etr etr icic. H • • h hy yd dro rog gen en p pero erox xi id de, e, H H O O 2 2 2 2  34.02 34.02 g g/m /mol ol. O O  pol pola ar r mo molec lecule ule  dip dipole ole– –dip dipole ole a att ttra rac cti tions ons pre present sent.  p Po olar lar H H− −O O b bo on nd ds s & an a ds a ys m ym mm etr etr icic. H H  H H− −O bonds O bonds  hy Hydrog drogen en-bon bondin ding g pre present. sent www.ThesisScientist.comPractice–Pick the Compound in Each Pair Expected to Have the Higher Solubility in H O. 2 • CH CH OCH CH or CH CH CH CH CH . 3 2 2 3 3 2 2 2 3 • CH CH NHCH or CH CH CH CH . 3 2 3 3 2 2 3 • CH CH OH or CH CH CH CH CH OH. 3 2 3 2 2 2 2 www.ThesisScientist.comPractice–Pick the Compound in Each Pair Expected to Have the Higher Solubility in H O, Continued. 2 • CH CH OCH CH or CH CH CH CH CH contains polar O. 3 2 2 3 3 2 2 2 3 • CH CH NHCH or CH CH CH CH contains polar N. 3 2 3 3 2 2 3 • CH CH OH or CH CH CH CH CH OH contains less nonpolar parts. 3 2 3 2 2 2 2 www.ThesisScientist.comTypes of Intermolecular Forces Type of Relative Present force strength in Example Weak, but All atoms Dispersion increases and H 2 force with molar molecules mass Dipole– Only Dipole Moderate polar HCl force molecules Molecules Hydrogen having H Strong HF bonded to Bond www.ThesisScientist.com F, O, or NCrystalline Solids www.ThesisScientist.comTypes of Crystalline Solids www.ThesisScientist.comMolecular Crystalline Solids • Molecular solids are solids whose composite units are molecules. • Solid held together by intermolecular attractive forces. Dispersion, dipole-dipole, or H-bonding. • Generally low melting points and DH . fusion www.ThesisScientist.comIonic Crystalline Solids • Ionic solids are solids whose composite units are formula units. • Solid held together by electrostatic attractive forces between cations and anions.  Cations and anions arranged in a geometric pattern called a crystal lattice to maximize attractions. • Generally higher melting points and DH than molecular solids. fusion  Because ionic bonds are stronger than intermolecular forces. www.ThesisScientist.comAtomic Crystalline Solids • Atomic solids are solids whose composite units are individual atoms. • Solids held together by either covalent bonds, dispersion forces, or metallic bonds. • Melting points and DH vary fusion depending on the attractive forces between the atoms. www.ThesisScientist.comPractice—Classify Each of the Following Crystalline Solids as Molecular, Ionic, or Atomic. • • H H O( O(s s) )—molecular. 2 2 • • Si( Si(s s) )—atomic. • • C C H H O O ( (s s) )—molecular. 12 12 22 22 11 11 • • CaF CaF ( (s s) )—ionic. 2 2 • • Sc( Sc(NO NO ) ) ( (s s) )—ionic. 3 3 3 3 www.ThesisScientist.comMetallic Bonding • The model of metallic bonding can be used to explain the properties of metals. • The luster, malleability, ductility, and electrical and thermal conductivity are all related to the mobility of the electrons in the solid. • The strength of the metallic bond varies, depending on the charge and size of the cations, so the melting points and DH of fusion metals vary as well. www.ThesisScientist.com
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