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1、Force of acting between molecules Range of existence:between atomsbond energy：100800 KJmol-1Chemical bonds:ionic bonds,metallic bonds and covalent bonds.Impact：The physicochemical properties of element and its compound Covalent bond is a general action.Apart from a few atomic crystals(such as diamon
2、d,quartz,etc.),most molecules exist via covalent bonding(such as HCl,H2O),and therefore form molecular crystal via inter-molecular forces,this force is also called van der Waals force,which is one of important parameters depending on the physical property.The intrinsic dipole of polar molecule is de
3、fined as permanent dipole.The dipole of nonpolar molecule is induced by polar molecule is called an induced dipole.The dipole caused by the separation of positive and negative charge center is called the instantaneous dipole,the main reason is due to the relative displacement of the constantly movin
4、g electrons and the constantly vibrating nucleus in a certain moment.Dispersion forceNonpolar moleculespolar moleculesNonpolar moleculespolar moleculesOrientation forceInduced forceInducedOrientationInstantaneous dipole interaction of nonpolar molecules The essence reasons for the intermolecular att
5、raction are due to:every molecule has positive and negative electrical centers and has the ability for deformation.Intermolecular actions is due to instantaneous dipoles.2.Intermolecular attraction1.Dispersion action(dispersion force):The general profileDispersion forces are related to molecular pol
6、arizability.increase with dispersion force increaseEvery moment 2.、色散力、色散力(dispersion force)（O2、N2、Cl2、稀气可液化或凝固，如何解释？、稀气可液化或凝固，如何解释？）定定义义由由于于存存在在“瞬瞬间间偶偶极极”而而产产生生的的相相互互作作用用力力过过程程电电子子的的运运动动、核核的的振振动动核核和和电电子子云云之之间间的的瞬瞬间间相相对对位位移移瞬瞬时时偶偶极极分分子子间间瞬瞬间间偶偶极极吸引。吸引。也叫伦敦力也叫伦敦力(London force)。范围范围所有分子之间所有分子之间 本质本质静电
7、静电 通常情况下非极性分子的正电荷重心与负电荷重心重合，通常情况下非极性分子的正电荷重心与负电荷重心重合，但原子核和电子的运动可导致电荷重心瞬间分离，从而产生但原子核和电子的运动可导致电荷重心瞬间分离，从而产生瞬间偶极瞬间偶极.瞬间偶极又使邻近的另一非极性分子产生瞬间诱瞬间偶极又使邻近的另一非极性分子产生瞬间诱导偶极，不难想像，两种偶极处于异极相邻状态导偶极，不难想像，两种偶极处于异极相邻状态。2.dispersion force O2,N2,Cl2 and noble gas can be liquefied or solidified,how to explain?Definition-P
8、rocess of interaction due to the presence of“instantaneous dipoles”-electron motion,nuclear vibration instantaneous relative displacement between nucleus and electron cloud instantaneous dipole intermolecular instantaneous dipole attraction.Also called as London Force.Normally,the center of positive
9、 charge overlap with that of negative charge in nonpolar molecules,however,the movement of the nucleus and the electron can cause the center of their charge to separate momentarily,thus generating a instantaneous dipole,which thereafter causes a instantaneous induced dipole in a neighboring nonpolar
10、 molecule,and it is not difficult to imagine that the two dipoles are adjacent to each other.It exists among all molecules.The essence belongs to static electricityThe dispersion force depends on both size and shape of the molecules(1)Propane,n-butane and n-pentane are straight chain compounds(the i
11、nfluence of molecular shape can be ignored),in which,the dispersion force increases with the increase of molecular volume,leading to the increase of boiling point in the following order:CH3CH2CH3 CH3CH2CH2CH3 CH3CH2CH2CH2CH3 b.p.-44.5 b.p.-0.5 b.p.36(2)The relative molecular mass of the n-pentane,is
12、opentane and neopentane are the same,and belong to the geometric isomers,their dispersion force decreases with the increase of the degree of molecular structure compactness,leading to the decrease of boiling point in the following order:CH3 CH3CH2CH2CH2CH3 CH3CH2CHCH3 CH3CCH3 CH3 CH3 b.p.36 b.p.28 b
13、.p.9.5(3)The dispersion force is dominant in most molecule except a few strong polar molecules(such as HF,H2O).Interactions between nonpolar moleculesInteractions between nonpolar moleculesInteractions between nonpolar moleculesInstant momentgenerally2.诱导作用诱导作用(诱导力诱导力)：决定诱导作用强弱的因素：决定诱导作用强弱的因素：极性分子的偶
14、极矩极性分子的偶极矩：愈大，诱导作用愈强。愈大，诱导作用愈强。非极性分子的极化率非极性分子的极化率：愈大，诱导作用愈强。愈大，诱导作用愈强。由于诱导偶极而产生的分子间相互作用。由于诱导偶极而产生的分子间相互作用。分子离得较远分子离得较远分子靠近时分子靠近时2.Induction action(induction force)：Factors that depend on the strength of induction:(1)dipole moments of polar molecules:The greater the,the stronger the induction effect.
15、(2)polarizability of nonpolar molecules:The greater the,the stronger the induction.due to the induced dipole of intermoleculesfar away each otherclose to together3.Orientation action(orientation force):due to the same pole repels,the opposite pole attracts between two inherent dipoles.far away each
16、othertend to orientation When the two polar molecules are close to each other,due to the repulsion of the same pole and the attraction of the opposite pole,the molecules rotation and their orientation according to the adjacent state of different poles result in that they are further close to each ot
17、her.Question1.What factors depending on orientation?2.Whats the interaction between polar molecules besides orientation?Intermolecular force is the general term for three kinds of attraction,and its size is around several kJmol-1,smaller 1-2 orders than that of chemical bond.Intermolecular attractio
18、n(10-22 J)Characteristics of intermolecular forces：In different cases,the composition of intermolecular forces is different.For example,there are only dispersion forces between nonpolar molecules,but in three kinds of forces between polar molecules the dispersion force is dominant,except for H2O wit
19、h strong polarity.The range of intermolecular forces is very small(general around 300-500 pm).The intermolecular forces are weak,neither direction nor saturation.molecular massdispersion effectintermolecular forceB.and M.pointSolubility in waterHeNeArKrXemolecular mass smalllargelargelargelarge lowh
20、ighsmalllarge depend on the physical properties of a substance such as melting,boiling point,heat of vaporization,heat of fusion,vapor pressure,solubility,and surface tension.The meaning of intermolecular forces:smallsmallsmall3.Hydrogen bondBoiling point(oC)Periodic number of elemental tableHF HCl
21、HBr HIboiling point/oC 19.9 -85.0 -66.7 -35.4 polarizability small largerdispersion effect weak strongboiling point/oC low highWhy is HF unusually high?reason the existence of hydrogen bonds.X -H +F、O、NF、O、NY -The formation conditions of hydrogen bond are as follows:Bond length:FH F 270pm Bond energ
22、y of around 28kJmol1 Direction and saturation Characteristics of hydrogen bond:H atom and the elements(F,O,N)with small radius,large electronegativity,and lone pair electronsSuch as:formic acid forms dimers by hydrogen bonds.HCOOHHOOHCFor example,the intramolecular hydrogen bonding of nitric acid le
23、ads to lower melting and boiling points.Besides that HF,H2O and NH3 have intermolecular hydrogen bonds,hydrogen bonds also exist in carboxylic acids,alcohols,phenols,amines,amino acids and proteins.Besides that intermolecular hydrogen bonds,there are intramolecular hydrogen bonds.Ice is less dense t
24、han water and therefore can float on water.The density of water is the highest at 4.Its effects on ice and water density:Reason:All water molecules are adjacent to each other with hydrogen bonds,and form an open structure with considerable gaps(density less than water).When ice melts some hydrogen b
25、onds are destroyed the open structure“collapses”liquid water has a high density,but still exists in the small structural groups of(H2O)n when the temperature rises.(H2O)nn(H2O),the water molecules are much closer together,d value thermal motion，V value,d valueWhen 0 4,the first factor is dominant,but the second factor is dominant after 4,so the density of water is the highest at 4（1.00g/ml）.