Periodic Relationships Among the Elements

Transcription

1 When the Elements Were Discovered Periodic Relationships Among the Elements Chapter 8 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2 ns 1 Ground State Electron Configurations of the Elements ns 2 ns 2 np 1 ns 2 np 2 ns 2 np 3 ns 2 np 4 ns 2 np 5 ns 2 np 6 Classification of the Elements d 1 d 5 d f 5f 3 4 Electron Configurations of Cations and Anions Of Representative Elements Cations and Anions Of Representative Elements Na [Ne]3s 1 Ca [Ar]4s 2 Al [Ne]3s 2 3p 1 Na + [Ne] Ca 2+ [Ar] Al 3+ [Ne] Atoms lose electrons so that cation has a noble-gas outer electron configuration. Atoms gain electrons so that anion has a noble-gas outer electron configuration. H 1s 1 H - 1s 2 or [He] F 1s 2 2s 2 2p 5 F - 1s 2 2s 2 2p 6 or [Ne] O 1s 2 2s 2 2p 4 O 2-1s 2 2s 2 2p 6 or [Ne] N 1s 2 2s 2 2p 3 N 3-1s 2 2s 2 2p 6 or [Ne] 5 6 1

2 Isoelectronic: have the same number of electrons, and hence the same ground-state electron configuration Na + : [Ne] Al 3+ : [Ne] F - : 1s 2 2s 2 2p 6 or [Ne] O 2- : 1s 2 2s 2 2p 6 or [Ne] N 3- : 1s 2 2s 2 2p 6 or [Ne] Electron Configurations of Cations of Transition Metals When 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. Na +, Al 3+, F -, O 2-, and N 3- are all isoelectronic with Ne What neutral atom is isoelectronic with H -? H - : 1s 2 same electron configuration as He Fe: [Ar]4s 2 3d 6 Fe 2+ : [Ar]4s 0 3d 6 or [Ar]3d 6 Fe 3+ : [Ar]4s 0 3d 5 or [Ar]3d 5 Mn: [Ar]4s 2 3d 5 Mn 2+ : [Ar]4s 0 3d 5 or [Ar]3d Effective nuclear charge (Z eff ) is the positive charge felt by an electron. Z eff = Z - s 0 < s < Z (s = shielding constant) Z eff Z number of inner or core electrons Effective Nuclear Charge (Z eff ) increasing Z eff Na Mg Al Z Core Z eff Radius (pm) increasing Z eff Si Atomic Radii metallic radius covalent radius

3 Trends in Atomic Radii Example With reference only to a periodic table, arrange each set of elements in order of increasing atomic radius: (a) Mg, S, Si (b) As, N, P (c) As, Sb, Se Comparison of Atomic Radii with Ionic Radii Cation is always smaller than atom from which it is formed. Anion is always larger than atom from which it is formed. 15 Isoelectronic species have the same electron configuration; size decreases with effective nuclear charge. P -3, S -2, Cl - <Ar, K +, Ca Some Atomic and Ionic Radii Example Refer to a periodic table and arrange the following species in the expected order of increasing radius: Ca 2+, Fe 3+, K +, S 2, Se

4 Increasing First Ionization Energy Chemistry in Action: The 3 rd Liquid Element? 117 elements, 2 are liquids at 25 0 C Br 2 and Hg Ionization energy is the minimum energy (kj/mol) required to remove an electron from a gaseous atom in its ground state. 223 Fr, t 1/2 = 21 minutes I 1 + X (g) X + (g) + e - I 2 + X + (g) X 2+ (g) + e - I 1 first ionization energy I 2 second ionization energy Liquid? I 3 + X 2+ (g) X 3+ (g) + e - I 3 third ionization energy I 1 < I 2 < I Successive Ionization Energies (KJ per Mole) for the Elements in Period Variation of the First Ionization Energy with Atomic Number Filled n=1 shell Filled n=2 shell General Trends in First Ionization Energies Increasing First Ionization Energy Filled n=3 shell Filled n=4 shell Filled n=5 shell

5 Increasing reactivity Electron affinity is the negative of the energy change that occurs when an electron is accepted by an atom in the gaseous state to form an anion. X (g) + e - X - (g) F (g) + e - X - (g) DH = -328 kj/mol EA = +328 kj/mol O (g) + e - O - (g) DH = -141 kj/mol EA = +141 kj/mol Variation of Electron Affinity With Atomic Number (H Ba) Diagonal Relationships on the Periodic Table Group 1A Elements (ns 1, n 2) Group 1A Elements (ns 1, n 2) M M e - 2M (s) + 2H 2 O (l) 4M (s) + O 2(g) 2MOH (aq) + H 2(g) 2M 2 O (s)

6 Increasing reactivity Group 2A Elements (ns 2, n 2) Group 2A Elements (ns 2, n 2) M M e - Be (s) + 2H 2 O (l) Mg (s) + 2H 2 O (g) M (s) + 2H 2 O (l) No Reaction Mg(OH) 2(aq) + H 2(g) M(OH) 2(aq) + H 2(g) M = Ca, Sr, or Ba Group 3A Elements (ns 2 np 1, n 2) Group 3A Elements (ns 2 np 1, n 2) 4Al (s) + 3O 2(g) 2Al (s) + 6H + (aq) 2Al 2 O 3(s) 2Al 3+ (aq) + 3H 2(g) Group 4A Elements (ns 2 np 2, n 2) Group 4A Elements (ns 2 np 2, n 2) Sn (s) + 2H + (aq) Pb (s) + 2H + (aq) Sn 2+ (aq) + H 2 (g) Pb 2+ (aq) + H 2 (g)

7 Increasing reactivity Group 5A Elements (ns 2 np 3, n 2) Group 5A Elements (ns 2 np 3, n 2) N 2 O 5(s) + H 2 O (l) P 4 O (s) + 6H 2 O (l) 2HNO 3(aq) 4H 3 PO 4(aq) Group 6A Elements (ns 2 np 4, n 2) Group 6A Elements (ns 2 np 4, n 2) SO 3(g) + H 2 O (l) H 2 SO 4(aq) Group 7A Elements (ns 2 np 5, n 2) Group 7A Elements (ns 2 np 5, n 2) X + 1e - X -1 X 2(g) + H 2(g) 2HX (g)

8 Group 8A Elements (ns 2 np 6, n 2) Compounds of the Noble Gases Completely filled ns and np subshells. Highest ionization energy of all elements. No tendency to accept extra electrons. 43 A number of xenon compounds XeF 4, XeO 3, XeO 4, XeOF 4 exist. A few krypton compounds (KrF 2, for example) have been prepared. 44 Comparison of Group 1A and 1B Properties of Oxides Across a Period The metals in these two groups have similar outer electron configurations, with one electron in the outermost s orbital. Chemical properties are quite different due to difference in the ionization energy. basic acidic Lower I 1, more reactive A Summary of Trends Chemistry in Action: Discovery of the Noble Gases 47 Sir William Ramsay 48 8