ChemicalBonding化学链接课件

1、ChemicalBonding化学链接,1,7,Chemical Bonding 化学键结,ChemicalBonding化学链接,2,Chapter Goals,1. Lewis Dot Formulas of Atoms 路易斯电子点结构式 Ionic Bonding 离子键结 2. Formation of Ionic Compounds 形成离子化合物 Covalent Bonding 共价键结 3. Formation of Covalent Bonds 形成共价键 4. Bond Lengths and Bond Energies 键长及键能 5. Lewis Formulas f

2、or Molecules and Polyatomic Ions 分子极多元子离子之路易斯结构式 6. Writing Lewis Formulas: The Octet Rule 八隅体法则 7. Formal Charges 形式电荷 8. Writing Lewis Formulas: Limitations of the Octet Rule 八隅体法则之限制 9. Resonance 共振 10. Polar and Nonpolar Covalent Bonds 极性及非极性共价键结 11. Dipole Moments 偶极距 12. The Continuous Range o

3、f Bonding Types 键结形式之连续范围,ChemicalBonding化学链接,3,Introduction,Attractive forces that hold atoms together in compounds are called chemical bonds (化合物中将原子拉进的吸引力称之为化学键结) The electrons involved in bonding are usually those in the outermost (valence) shell (与键结有关的电子通常是指最外层的电子,ChemicalBonding化学链接,4,Introdu

4、ction,Chemical bonds are classified into two types: Ionic bonding 离子键结 results from electrostatic attractions among ions, which are formed by the transfer of one or more electrons from one atom to another. 离子键为阳离子与阴离子间之库伦静电力，阳离子由金属失去电子形成，阴离子由非金属得到电子形成。两正负电荷之离子吸引力，称为离子键。 Ionic compound 离子化合物 NaCl Cov

5、alent bonding 共价键结 results from sharing one or more electron pairs between two atoms. 价键为两原子共享电子对之化学键，其结合原子皆为非金属原子 Covalent compound H2, Cl2,ChemicalBonding化学链接,5,ChemicalBonding化学链接,6,Lewis Dot Formulas of Atoms 原子的路易斯电子点结构式,Lewis dot formulas or Lewis dot representations are a convenient bookkeepi

6、ng method for tracking valence electrons 价电子. The electrons in the outermost occupied shells (最外层的电子数) s and p orbitals Valence electrons are those electrons that are transferred or involved in chemical bonding (价电子是指与化学键结有关或转移的电子) They are chemically important,ChemicalBonding化学链接,7,Lewis Dot Formul

7、as 路易斯结构 of Atoms,Elements that are in the same periodic group have the same Lewis dot structures (同族元素具相同路易斯结构,1 electron in valence shell,5 electrons in valence shell,Not as useful for the transition and inner transition elements (不适用于过渡元素,ChemicalBonding化学链接,8,Ionic Bonding 离子键结,Formation of Ioni

8、c Compounds 形成离子化合物 An ion is an atom or a group of atoms possessing a net electrical charge. Ions come in two basic types: positive (+) ions or cations These atoms have lost 1 or more electrons. negative (-) ions or anions These atoms have gained 1 or more electrons,ChemicalBonding化学链接,9,Formation

9、of Ionic Compounds,Monatomic ions consist of one atom. Examples: Na+ sodium ion, Ca2+, Al3+ - cations Cl- chloride ion, O2-, N3- - anions Polyatomic ions contain more than one atom. Examples: NH4+ ammonium ion - cation NO2-, CO32-, SO42- sulfate ion anions The atoms of a polyatomic ion are held toge

10、ther by covalent bonds (多原子离子之原子间以共价键结,ChemicalBonding化学链接,10,Elements that have low electronegativities and low ionization enengy metals (oxidozed; lose electrons to form cations) Elements that have high electronegativities and very negative electron affinities nonmetals (reduced; gain electrons to

11、 form anions,Ionic Bonding is the attraction of oppositely charged ions (cations and anions) in large numbers to form a solid. Such a solid compound is called an ionic solid,React,Ionic compound,ChemicalBonding化学链接,11,Formation of Ionic Compounds,Reaction of Group IA Metals with Group VIIA Nonmetals

12、,1A metal 7A nonmetal 2Li(s) + F2(g) 2LiF(s) Silver yellow white solid Solid gas with an 842oC melting point,ChemicalBonding化学链接,12,Formation of Ionic Compounds,The underlying reason for the formation of LiF lies in the electron configurations of Li and F. 1s 2s 2p Li F These atoms form ions with th

13、ese configurations. Li+ same configuration as He loss one electron F- same configuration as Ne gained one electron,Li+ isoelectronic with He,等电子离子,F+ isoelectronic with Ne,ChemicalBonding化学链接,13,Formation of Ionic Compounds,We can also use Lewis dot formulas to represent the neutral atoms and the io

14、ns they form,ChemicalBonding化学链接,14,Formation of Ionic Compounds,The Li+ ion contains two electrons, same as the helium atom. Li+ ions are isoelectronic 等电子离子 with helium. The F- ion contains ten electrons, same as the neon atom. F- ions are isoelectronic with neon. Isoelectronic species contain the

15、 same number of electrons. Most ionic compounds formed by reactions between representative metals 典型金属and representative nonmetals 典型非金属,ChemicalBonding化学链接,15,Formation of Ionic Compounds,The reaction of potassium with bromine is a second example of a group IA metal with a Group VIIA non metal. Wri

16、te the reaction equation,1A metal 7A nonmetal 2K(s) + Br2(g) 2KBr(s) ionic solid,ChemicalBonding化学链接,16,Formation of Ionic Compounds,We look at the electronic structures of K and Br. 4s 4p K Ar Br Ar and the d electrons The atoms form ions with these electronic structures. 4s 4p K+ same configuratio

17、n as Ar Br- same configuration as Kr,ChemicalBonding化学链接,17,Formation of Ionic Compounds,Write the Lewis dot formula representation for the reaction of K and Br,ChemicalBonding化学链接,18,Formation of Ionic Compounds,There is a general trend evident in the formation of these ions. Cations become isoelec

18、tronic with the preceding noble gas. 之前的钝气 Anions become isoelectronic with the following noble gas. 之后的钝气,ChemicalBonding化学链接,19,Formation of Ionic Compounds,In general for the reaction of IA metals and VIIA nonmetals, the reaction equation is: 2 M(s) + X2 2 M+ X-(s) where M is the metals Li to Cs

19、and X is the nonmetals F to I. Electronically this is occurring. ns np ns np M M+ X X-,ChemicalBonding化学链接,20,Formation of Ionic Compounds,Next we examine the reaction of IIA metals with VIIA nonmetals. This reaction forms mostly ionic compounds. Notable exceptions are BeCl2, BeBr2, and BeI2 which a

20、re covalent compounds. One example is the reaction of Be and F2. Be(s) + F2(g) BeF2(g,ChemicalBonding化学链接,21,Formation of Ionic Compounds,The valence electrons in these two elements are reacting in this fashion. 2s 2p 2s 2p Be He Be2+ F He F- Next, draw the Lewis dot formula representation of this r

21、eaction,ChemicalBonding化学链接,22,Formation of Ionic Compounds,The remainder of the IIA metals and VIIA nonmetals react similarly. Symbolically this can be represented as: M(s) + X2 M2+ X2- M can be any of the metals Be to Ba. X can be any of the nonmetals F to Cl,ChemicalBonding化学链接,23,Formation of Io

22、nic Compounds,For the reaction of IA metals with VIA nonmetals, a good example is the reaction of lithium with oxygen. The reaction equation is,ChemicalBonding化学链接,24,Formation of Ionic Compounds,Draw the electronic configurations for Li, O, and their appropriate ions. 2s 2p 2s 2p Li He Li1+ O He O2

23、- Draw the Lewis dot formula representation of this reaction,ChemicalBonding化学链接,25,Formation of Ionic Compounds,The remainder of the IA metals and VIA nonmetals behave similarly. Symbolically this can be represented as: 2 M (s) + X M21+ X- M can be any of the metals Li to Cs. X can be any of the no

24、nmetals O to Te,ChemicalBonding化学链接,26,Formation of Ionic Compounds,The reaction of IIA metals and VA nonmetals also follows the trends that we have established in this chapter. The reaction of calcium with nitrogen is a good example. The reaction equation is: 3Ca(s) + N2(g) Ca3N2 (s,ChemicalBonding

25、化学链接,27,Formation of Ionic Compounds,Draw the electronic representation of Ca, N, and their ions. 4s 4p 4s 4p Ca Ar Ca2+ 2s 2p 2s 2p N He N3- Draw the Lewis dot representation of this reaction,ChemicalBonding化学链接,28,Formation of Ionic Compounds,Other IIA and VA elements behave similarly. Symbolicall

26、y, this reaction can be represented as: 3 M(s) + 2 X(g) M32+ X23- M can be the IIA elements Be to Ba. X can be the VA elements N to As,ChemicalBonding化学链接,29,Formation of Ionic Compounds,d-transition Metal Ions The outermost s electrons and energy level lower d electrons are always the first ones lo

27、st when transition metals form simple ions,3d 4s 3d 4s ScAr Sc3+Ar 3e- lost ZnAr Zn2+Ar 2e- lost Most other 3d-transition metals can form at least two cations in their compounds. 3d 4s 3d 4s CoAr Co2+Ar 2e- lost CoAr Co3+Ar 3e- lost,钪,ChemicalBonding化学链接,30,Formation of Ionic Compounds,H, a nonmetal

28、, forms ionic compounds with IA and IIA metals for example, LiH, KH, CaH2, and BaH2. Other hydrogen compounds are covalent,Group IA and IIA can form peroxide (contain O22- ion ) or superoxide (contain O2- ion). The peroxide and superoxide ions contain atoms that are covalently bonded to one another,

29、3A,ChemicalBonding化学链接,31,31,Group IA and IIA can form peroxide (contain O22- ion ) or superoxide (contain O2- ion). The peroxide and superoxide ions contain atoms that are covalently bonded to one another,ChemicalBonding化学链接,32,Formation of Ionic Compounds,Ionic compounds form extended three dimens

30、ional arrays of oppositely charged ions. Ionic compounds have high melting points because the coulomb force库仑力, which holds ionic compounds together, is strong,ChemicalBonding化学链接,33,Formation of Ionic Compounds,Coulombs Law describes the attraction of positive ions for negative ions due to the oppo

31、site charges,ChemicalBonding化学链接,34,Formation of Ionic Compounds,Small ions with high ionic charges have large Coulombic forces of attraction. Large ions with small ionic charges have small Coulombic forces of attraction. Use this information, plus the periodicity rules from Chapter 6, to arrange th

32、ese compounds in order of increasing attractions among ions KCl, Al2O3, CaO,ChemicalBonding化学链接,35,Covalent Bonding 共价键结,Covalent bonds are formed when atoms share electrons. It Occurs when the electronegativity difference between elements (atoms) is zero or relativity small (电负度几乎没差) The bonds betw

33、een atoms within a molecule (intramolecular bonds 分子内键结) are relatively strong, but the force of attraction between molecules (intermolecular forces 分子间键结) are relatively weak lower melting and boiling points than ionic compound (较离子化合物的熔点及沸点低) If the atoms share 2 electrons a single covalent bond i

34、s formed (若原子共享2个电子则形成单一共价键) If the atoms share 4 electrons a double covalent bond is formed (若原子共享4个电子则形成二个共价键) If the atoms share 6 electrons a triple covalent bond is formed (若原子共享6个电子则形成三个共价键) The attraction between the electrons is electrostatic in nature The atoms have a lower potential energy

35、 when bound,ChemicalBonding化学链接,36,Formation of Covalent Bonds,Representation of the formation of an H2 molecule from H atoms,The electron of each atom is attracted by the positively charged nucleus of the other atom, so the electron density begins to shift (blue arrows) (电子受到带正电的原子核的吸引, 电子团开始变化 ) T

36、he electron clouds of the two atoms repel one another, and so do the nuclei of the two atoms (Red arrows) (两个原子亦会有排斥力,The two 1s orbitals overlap,ChemicalBonding化学链接,37,Formation of Covalent Bonds,This figure shows the potential energy of an H2 molecule as a function of the distance between the two

37、H atoms,For any covalent bond there is an internuclear distance where the attractive and repulsive forces balance. This distance is the bond length (彼此间的距离称键长). The energy difference is the bond energy (能量的差异称为键能,太靠近,产生斥力,太远,引力太小,无键结,斥力与引力达成平衡,稳定的排列,ChemicalBonding化学链接,38,Bond dissociation energy 键离

38、解能 Bond energy 键能,ChemicalBonding化学链接,39,ChemicalBonding化学链接,40,Formation of Covalent Bonds,We can use Lewis dot formulas to show covalent bond formation. H molecule formation representation,2. HF molecule formation,H + H H:H or H-H,3. F2 molecule formation,ChemicalBonding化学链接,41,H2O H O CO2 NH4+ N:

39、 5 electrons H: 1 electrons Total 9 electrons,or,Dot formula,Dash formula线结构式,ChemicalBonding化学链接,42,Writing Lewis Formulas:The Octet Rule八隅体法则,N - A = S rule Simple mathematical relationship to help us write Lewis dot formulas. N = number of electrons needed to achieve a noble gas configuration. (要

40、达到钝气组态的电子数目,通常为8) N usually has a value of 8 for representative elements. N has a value of 2 for H atoms. A = number of electrons available in valence shells of the atoms. (原子的价电子数) A is equal to the periodic group number for each element. A is equal to 8 for the noble gases. S = number of electrons

41、 shared in bonds. (形成键结可共享的电子数) A-S = number of electrons in unshared, lone, pairs. (不共享的电子数,又称孤电子对,ChemicalBonding化学链接,43,Lewis Formulas for Molecules and Polyatomic Ions,First, we explore Lewis dot formulas of homonuclear diatomic molecules. Two atoms of the same element. Hydrogen molecule, H2,2.

42、Fluorine, F2,Nitrogen, N2,H:H or HH,or,or,N=2x8=16 e- needed A=2x7=14 e- available S=N-A=2 e- shared,N=2x2=4 e- needed A=2x1=2 e- available S=N-A=2 e- shared,N=2x8=16 e- needed A=2x5=10 e- available S=N-A=6 e- shared 2 molecule with 6 electrons 3 covalent bond,ChemicalBonding化学链接,44,Lewis Formulas f

43、or Molecules and Polyatomic Ions,Next, look at heteronuclear diatomic molecules. Two atoms of different elements. Hydrogen halides 卤化氢 are good examples. hydrogen fluoride, HF,2. hydrogen chloride, HCl,3. hydrogen bromide, HBr,or,or,or,N=1x2+1x8=10 e- needed A=1x1+1x7=8 e- available S=N-A=2 e- share

44、d,ChemicalBonding化学链接,45,Lewis Formulas for Molecules and Polyatomic Ions,Now we will look at a series of slightly more complicated heteronuclear molecules. Water, H2O,or,Ammonia molecule , NH3,or,N=2x2+1x8=12 e- needed A=2x1+1x6=8 e- available S=N-A=4 e- shared,N=3x2+1x8=14 e- needed A=3x1+1x5=8 e-

45、 available S=N-A=6 e- shared,ChemicalBonding化学链接,46,Lewis Formulas for Molecules and Polyatomic Ions,Lewis formulas can also be drawn for molecular ions. One example is the ammonium ion , NH4,Notice that the atoms other than H in these molecules have eight electrons around them,N=1x8+4x2=16 e- need

46、1C atom 4H atom A=1x5+4x1-1=8e- available 1C atom 4H atom (+1charge) S=N-A=16-8=8e- share,ChemicalBonding化学链接,47,A Guild to Writing Lewis Formulas,Select a reasonable (symmetrical) “skeleton” for the molecule or polyatomic ion 选择最合理分子当作骨架 The least electronegative element is usually the central elem

47、ent, except the H 电负度最小者通常为中心分子,氢除外 Carbon bonds to two, three or four atoms, but never more than four 碳可与2, 3及4个原子键结 Oxygen atoms do not bond to each other except in (氧原子不会键结在一起,除非) O2 and O3 hydrogen peroxide, H2O2, and the peroxide contain the O22- group Superoxide, which contain the O2- group In

48、 ternary oxoacids, hydrogen usually bond to an O atom, not to the central atom, HNO2 三元含氧酸中,氢通常与氧键结 For those have more than one central atom, the most symmetrical skeletons possible are used, such as C2H4, P2O74,ChemicalBonding化学链接,48,A Guild to Writing Lewis Formulas,2. Calculate N, the number of

49、valence shell electrons needed by all atoms in the molecule or iron to achieve noble gas configurations PF3 N=1x8(P atom)+3x8(F atoms) = 32e- need CH3OH N=1x8(C atom)+4x2(H atoms)+1x8 (O atom) = 24e- need NO3- N=1x8(N atom)+3x8(O atoms) = 32e- need Calculate A, the number of electrons available in t

50、he outer shells of all the atoms PF3 A=1x5(P atom)+3x7(F atoms) = 26e- available CH3OH A=1x4(C atom)+4x1(H atoms)+1x6 (O atom) = 14e- available NO3- A=1x5(N atom)+3x6(O atoms)+1 (for 1-charge) = 24e- available,ChemicalBonding化学链接,49,A Guild to Writing Lewis Formulas,Calculate S, total number of elec

51、trons shared in the molecule or ion, using the relationship S=N-A PF3 S=N-A = 32-26=6 e- shared (3 pairs of e-shared) CH3OH S=24-14= 10 e- shared (5 pairs of e-shared) NO3- S= 32-24=8 e- hared (4 pairs of e-shared,ChemicalBonding化学链接,50,3. Place the S electron in to the skeleton as shared pairs. Use

52、 double and triple bonds only when necessary,S=6,S=10,S=8,3 pairs of e-shared,5 pairs of e-shared,4 pairs of e-shared,ChemicalBonding化学链接,51,4. Check the additional electrons into the skeleton as unshared pairs to fill the octet of every A group element (except H, shared only 2e,NO3,PF3,CH3OH,Chemic

53、alBonding化学链接,52,Writing Lewis Formulas:The Octet Rule,The octet rule states that representative elements usually attain stable noble gas electron configurations in most of their compounds. Lewis dot formulas are based on the octet rule. We need to distinguish between bonding (or shared) electrons a

54、nd nonbonding (or unshared or lone pairs) of electrons,ChemicalBonding化学链接,53,Writing Lewis Formulas:The Octet Rule,Example 7-2: Write Lewis dot and dash formulas for hydrogen cyanide, HCN. N = 2 (H) + 8 (C) + 8 (N) = 18 A = 1 (H) + 4 (C) + 5 (N) = 10 S = 8 A-S = 2 This molecule has 8 electrons in s

55、hared pairs and 2 electrons in lone pairs,or,ChemicalBonding化学链接,54,Writing Lewis Formulas:The Octet Rule,Example 7-3: Write Lewis dot and dash formulas for the sulfite ion, SO32-. N = 8 (S)+3 x 8 (O) = 32 A = 6 (S)+3 x 6 (O)+ 2 (- charge)= 26 S = 6 A-S = 20 Thus this polyatomic ion has 6 electrons

56、in shared pairs and 20 electrons in lone pairs. Which atom is the central atom in this ion,ChemicalBonding化学链接,55,Writing Lewis Formulas:The Octet Rule,What kind of covalent bonds, single, double, or triple, must this ion have so that the six shared electrons are used to attach the three O atoms to

57、the S atom,or,ChemicalBonding化学链接,56,Example 7-1 Writing Lewis Formula Write the Lewis formula for the nitrogen molecule, N2, carbon disulfide, CS2 and the carbonate ion, CO32- (a) N2 (b) CS2 (b) CO32,or,N=2x8=16 e- needed A=2x5=10 e- available S=N-A=6 e- shared 2 molecule with 6electrons 3 covalent

58、 bond,N=1x8+2x8=24 e- needed A=1x4+2x6=16 e- available S=N-A=8 e- shared 3 molecule with 8 electrons 2x2 covalent bond,or,N=1x8+3x8=32 e- needed A=1x4+3x6+2=24 e- available S=N-A=8 e- shared Four pairs are shared,or,Exercise 29, 30, 38,ChemicalBonding化学链接,57,hydrocarbon,乙烯,乙炔,乙烷,甲烷,甲醛,氯仿,三氯甲烷,乙醇,酒精,

59、ChemicalBonding化学链接,58,Formal Charge 形式电荷,Calculation of a formal charge on a molecule is a mechanism for determining correct Lewis structures The formal charge is the hypothetical charge on an atom in a molecule or polyatomic ion. The best Lewis structures will have formal charges on the atoms that

60、 are zero or nearly zero. 形式电荷：基于共享电子对由两键结原子平分共享的原则下，此原子的价电子数与在自由原子状态的价电子数两者的差值,ChemicalBonding化学链接,59,Formal Charge,Rules for Assigning Formal Charge Formal Charge = group number (number of bonds + number of unshared e-) An atom that has the same number of bonds as its periodic group number has a f