无机化学课件：04 Periodic

1、Chemistry: Atoms FirstJulia Burdge & Jason OverbyCopyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.Chapter 4Periodic Trendsof the ElementsPeriodic Trends of the Elements44.1Development of the Periodic Table4.2The Modern Periodic TableClassification of Elem

2、ents4.3Effective Nuclear Charge4.4Periodic Trends in Properties of ElementsAtomic RadiusIonization EnergyElectron AffinityMetallic Character4.5Electron Configuration of IonsIons of Main Group ElementsIons of d-Block Elements4.6Ionic RadiusComparing Ionic Radius with Atomic RadiusIsoelectronic Series

3、Development of the Periodic TableIn 1864, John Newlands noted that when the elements were arranged in order of atomic number that every eighth element had similar properties.He referred to this as the law of octaves.In 1869, Dmitri Mendeleev and Lothar Meyer independently proposed the idea of period

4、icity.Mendeleev grouped elements (66) according to properties.Mendeleev predicted properties for elements not yet discovered, such as Ga.4.1Development of the Periodic TableHowever, Mendeleev could not explain inconsistencies such as argon coming before potassium in the periodic table, despite havin

5、g a higher atomic mass.In 1913, Henry Moseley discovered the correlation between the number of protons (atomic number) and frequency of X-rays generated.Ordering the periodic table by atomic number instead of atomic mass enabled scientists to make sense of discrepancies.Entries today include atomic

6、number and symbol; and are arranged according to electron configuration.What elements would you expect to exhibit properties most similar to those of chlorine? Worked Example 4.1Solution Fluorine, bromine, and iodine, the other nonmetals in Group 7A, should have properties most similar to those of c

7、hlorine. Strategy Because elements in the same group tend to have similar properties, you should identify elements in the same group (7A) as chlorine.Think About It Astatine (At) is also in Group 7A. Astatine, though, is classified as a metalloid, and we have to be careful comparing nonmetals to met

8、alloids (or to metals). As a metalloid, the properties of astatine should be less similar to those of chlorine than the other members of Group 7A.The Modern Periodic Table4.2Classification of ElementsThe main group elements (also called the representative elements) are the elements in Groups 1A thro

9、ugh 7A.Classification of ElementsThe noble gases are found in Group 8A and have completely filled p subshells.The Modern Periodic TableThe transition metals are found in Group 1B and 3B through 8B.Group 2B have filled d subshells and are not transition metals.The Modern Periodic TableThe lanthanides

10、 and actinides make up the f-block transition elements.The Modern Periodic TableThere is a distinct pattern to the electron configurations of the elements in a particular group.For Group 1A: noble gasns1For Group 2A: noble gasns2The Modern Periodic TableThe outermost electrons of an atom are called

11、the valence electrons.Valence electrons are involved in the formation of chemical bonds.Similarity of valence electron configurations help predict chemical properties.For Group 1A: noble gasns1valencecoreFor Group 2A: noble gasns2valencecoreFor Group 7A: noble gasns2np5valencecoreWithout using a per

12、iodic table, give the ground-state electron configuration and block designation (s-, p-, d-, or f-block) of an atom with (a) 17 electrons, (b) 37 electrons, and (c) 22 electrons. Classify each atom as a main group element or transition metal. Worked Example 4.2Solution 1s22s22p63s23p5, p-block, main

13、 group1s22s22p63s23p64s23d104p65s1, s-block, main group1s22s22p63s23p64s23d2, d-block, transition metalStrategy Use the figure at right to assign electrons to orbitals in the correct order. Recall that an s subshell has one orbital, a p subshell has three orbitals, and a d subshell has five orbitals

14、. Remember, too, that each orbital can accommodate a maximum of two electrons.Think About It Consult the figure to confirm your answer.Effective Nuclear ChargeEffective nuclear charge (Zeff) is the actual magnitude of positive charge that is “experienced” by an electron in the atom.In a multi-electr

15、on atom, electrons are simultaneously attracted to the nucleus and repelled by one another.This results in shielding, where an electron is partially shielded from the positive charge of the nucleus by the other electrons.Although all electrons shield one another to some extent, the most effective ar

16、e the core electrons.As a result, the value of Zeff increases steadily from left to right because the core electrons remain the same but Z increases.LiBeBCNOFZ3456789Zeff 1.281.912.423.143.834.455.104.3Effective Nuclear ChargeIn general, the effective nuclear charge is given byZ is the nuclear charg

17、e or simply the number of protons in the nucleus. is the shielding constant.Zeff increases from left to right across a period; changes very little down a column.Zeff = Z LiBeBCNOFZ3456789Zeff 1.281.912.423.143.834.455.104.3Periodic Trends in Properties of ElementsAtomic radius is the distance betwee

18、n the nucleus of an atom and its valence shell.4.4(a) Atomic radius in metals, or metallic radius, is half the distance between the nuclei of two adjacent, identical metal atoms.(b) Atomic radius in nonmetals, or covalent radius, is half the distance between adjacent, identical nuclei connected by a

19、 chemical bond.Atomic RadiusThe atomic radius increases from top to bottom down a group.Increasing n, so outermost shell lies farther from the nucleusAtomic radius decreases from left to right across a period.Increasing Zeff which draws the valence shell closer to the nucleusAtomic radii (in picomet

20、ers)Atomic RadiusAtomic radius decreases left to right across a period due to increased electrostatic attraction between the effective nuclear charge and the charge on the valence shell.Referring only to a periodic table, arrange the elements P, S, and O in order of increasing atomic radius. Worked

21、Example 4.3Solution O S IE1(Na) because Mg is to the right of Na in the periodic table (i.e., Mg has the greater Zeff, so it is more difficult to remove its electron).IE2(Na) IE2(Mg) because the second ionization of Mg removes a valence electron, whereas the second ionization of Na removes a core el

22、ectron.Strategy Consider effective nuclear charge and electron configuration to compare the ionization energies. Na has one valence electron and Mg has two.Think About It The first ionization energies of Na and Mg are 496 and 738 kJ/mol, respectively. The second ionization energies of Na and Mg are

23、4562 and 1451 kJ/mol, respectively.Electron AffinityElectron affinity (EA) is the energy released when an atom in the gas phase accepts an electron.Cl(g) + e Cl(g)Electron AffinityLike ionization energy, electron affinity increases from left to right across a period as Zeff increases.Easier to add a

24、n electron as the positive charge of the nucleus increases.Electron AffinityIt is easier to add an electron to an s orbital than to add one to a p orbital with the same principal quantum number.Electron AffinityWithin a p subshell, it is easier to add an electron to an empty orbital than to add one

25、to an orbital that already contains an electron.ProcessElectron AffinityElectron AffinityMore than one electron may be added to an atom.While many first electron affinities are positive, subsequent electron affinities are always negative.Considerable energy is required to overcome the repulsive forc

26、es between the electron and the negatively charged ion.O(g) + e O(g)O (g) + e O2(g)EA1 = 141 kJ/molEA2 = 741 kJ/molFor each pair of elements, indicate which one you would expect to have the greater first electron affinity, EA1: (a) Al or Si, (b) Si or P. Worked Example 4.5Solution EA1(Si) EA1(Al) be

27、cause Si is to the right of Al and therefore has a greater Zeff.EA1(Si) EA1(P) because although P is to the right of Si, adding an electron to a P atom requires placing it in a partially occupied 3p orbital. The energy cost of pairing electrons outweighs the energy advantage of adding an electron to

28、 an atom with a larger Zeff.Strategy Consider effective nuclear charge and electron configuration to compare the ionization energies. (a) Al is in Group 3A and Si is in Group 4A. Al has three valence electrons (Ne3s23p1), and Si has four valence electrons (Ne3s23p2). (b) P is in Group 5A, so it has

29、five valence electrons (Ne3s23p3).Think About It The first electron affinities of Al, Si, and P are 42.5, 134, and 72.0 kJ/mol, respectively.Metallic CharacterMetals tend to Be shiny, lustrous, malleable, and ductile Be good conductors of both heat and electricity Have low ionization energies (commo

30、nly form cations)Metallic CharacterNonmetals tend to Vary in color and are not shiny Be brittle, rather than malleable Be poor conductors of both heat and electricityHave high electron affinities (commonly form anions)Metallic CharacterMetalloids are elements with properties intermediate between tho

31、se of metals and nonmetals.Metallic CharacterMany of the periodic trends of the elements can be explained using Coulombs law, which states that the force (F) between two charged objects (Q1 and Q2) is directly proportional to the product of the two charges and inversely proportional to the distance

32、(d) between the objects squared.F Q1Q2d2For carbon and nitrogen, use their effective nuclear charges and atomic radii to compare the attractive force between the nucleus in each atom and the valence electron that would be removed by the first ionization. Worked Example 4.6Solution For C: F For N: F

33、Note that it doesnt matter what units we use for the distance between the charges. We are not trying to calculate a particular attractive force, only compare the magnitude of these two attractive forces.Strategy Zeff for C and N are 3.14 and 3.83, respectively; the radii of C and N are 77 pm and 75

34、pm, respectively. IE1 are 1086 kJ/mol (C) and 1402 kJ/mol (N). The charge on the valence electron in each case is -1.(3.14)(-1)(77 pm)2= -5.310-4(3.83)(-1)(75 pm)2= -6.810-4Think About It The negative sign indicates that the force is attractive rather than repulsive. The calculated number for nitrog

35、en is about 28 percent larger than for carbon.Electron Configurations of IonsTo write the electron configuration of an ion formed by a main group element: Write the configuration for the atom. Add or remove the appropriate number of electrons.Na: 1s22s22p63s1Na+: 1s22s22p6Cl: 1s22s22p63s23p5Cl : 1s2

36、2s22p63s23p610 electrons total, isoelectronic with Ne18 electrons total, isoelectronic with Ar4.5Electron Configuration of Anions and CationsCations lose electrons to achieve a more stable configurationnontransition metalstransition metals through loss of s and then n-1 d electrons form more than on

37、e cationheavy nontransition metals inert pair effectWrite electron configurations for the following ions of main group elements: (a) N3-, (b) Ba2+, and (c) Be2+. Worked Example 4.7Solution He2s22p6 or NeKr5s24d105p6 or Xe1s2 or HeStrategy First write electron configurations for the atoms. Then add e

38、lectrons (for anions) and remove electrons (for cations) to account for the charge.Think About It Be sure to add electrons to form an anion, and remove electrons to form a cation.Ions of d-Block ElementsIons of d-block elements are formed by removing electrons first from the shell with the highest v

39、alue of n.For Fe to form Fe2+, two electrons are lost from the 4s subshell not the 3d.Fe can also form Fe3+, in which case the third electron is removed from the 3d subshell.Fe: Ar4s23d 6Fe2+: Ar3d 6Fe: Ar4s23d 6Fe3+: Ar3d 5Electron Configurations of Cations of Transition MetalsFe: Ar4s23d6Fe2+: Ar4

40、s03d6 or Ar3d6Fe3+: Ar4s03d5 or Ar3d5Mn: Ar4s23d5Mn2+: Ar4s03d5 or Ar3d5When a cation is formed from an atom of a transition metal, electrons are always removed first from the ns orbital and then from the (n 1)d orbitals.Write electron configurations for the following ions of d-block elements: (a) Z

41、n2+, (b) Mn2+, and (c) Cr3+. Worked Example 4.8Solution Ar3d10Ar3d5Ar3d3Strategy First write electron configurations for the atoms. Then add electrons (for anions) and remove electrons (for cations) to account for the charge. The electrons removed from a d-block element must come first from the oute

42、rmost s subshell, not the partially filled d subshell.Think About It Be sure to add electrons to form an anion, and remove electrons to form a cation. Also, double-check to make sure that electrons removed from a d-block elment come first from the ns subshell and then, if necessary, from the (n 1)d

43、subshell.Ionic RadiusThe ionic radius is the radius of a cation or an anion.When an atom loses an electron to become a cation, its radius decreases due in part to a reduction in electron-electron repulsions in the valence shell.A significant decrease in radius occurs when all of an atoms valence electrons are removed.4.6Comparing Ionic Radius with Atomic RadiusWhen an atom gains one or more electrons and becomes an anion, its radius increases due to increased electron-electron repulsio