Periodic Relationships Among the Elements Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Chapter Periodic classification of the elements. 8.3 Periodic variation in physical properties. 8.4 Ionization energy. 8.5 Electron affinity.

8.1 When the Elements Were Discovered

8.2 ns 1 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 d1d1 d5d5 d 10 4f 5f Ground State Electron Configurations of the Elements (IUPAC)

8.2 Classification of the Elements The nonsequential numbering of the transition metals in the periodic table (that is, 3B-8B, followed by 1B-2B) acknowledges a correspondence between the outer electron configurations of these elements and those of the representative elements. They are placed in different groups (3B and 3A) because they are in different types of atomic orbitals.

Worked Example 8.1

Representing Free Elements in Chemical Equations 1.Chemists always use the empirical formulas to represent metals and metalloids in chemical equations, such as Fe, Na, and B, Si, Ge. 2.For nonmetals there is no single rule. - Carbon, for example, exists in its empirical formula (C) but hydrogen, nitrogen, oxygen, and halogens exist as diatomic molecules [H 2, N 2, O 2,and X 2 (F 2, Cl 2, Br 2 ….]. - The stable form of phosphorus is P 4 and S 8 for sulfur but for sulfur, chemists often use the empirical formula (S) in chemical equations, rather than S 8 S + O 2 S O 2

Electron Configurations of Cations and Anions Na [Ne]3s 1 Na + [Ne] Ca [Ar]4s 2 Ca 2+ [Ar] Al [Ne]3s 2 3p 1 Al 3+ [Ne] Atoms lose electrons so that cation 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] Atoms gain electrons so that anion has a noble-gas outer electron configuration. Of Representative Elements 8.2

Cations and Anions Of Representative Elements 8.2

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] Na +, Al 3+, F -, O 2-, and N 3- are all isoelectronic with Ne. isoelectronic is the atoms have the same number of electrons, and hence the same ground- state electron configuration. What neutral atom is isoelectronic with H - ? H - : 1s 2 same electron configuration as He 8.2

Electron Configurations of Cations of Transition Metals 8.2 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. 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 5

8.3 Atomic radius is one-half the distance between the two nuclei in two adjacent metal atoms (a) or in a diatomic molecule (b).

8.3 The larger the effective nuclear charge, the stronger the hold of the nucleus on the outer-shell electrons, and the smaller the atomic radius.

Atomic Radii 8.3

Worked Example 8.2

8.3 Ionic radius is the radius of a cation or an anion. For the cation and the anion, the nuclear charge remains the same but in the anion the repulsion resulting from the additional electronal enlarges the domain of the electron cloud while in the cation removing one ore more electrons from an atom reduces electron-electron repulsion, so the electron cloud shrinks. Cation is always smaller than atom from which it is formed. Anion is always larger than atom from which it is formed.

Comparison of Atomic Radii with Ionic Radii

8.3 The Radii (in pm) of Ions of Familiar Elements

Chemistry in Action: The 3 rd Liquid Element? Liquid? 113 elements, 2 are liquids at 25 0 C – Br 2 and Hg 223 Fr, t 1/2 = 21 minutes Variation of physical properties across a period and within a group. From left to right across a period there is a transition from metals to metalloids to nonmetals and within a periodic group the physical properties vary more predictably.

Ionization energy is the minimum energy (kJ/mol) required to remove an electron from a gaseous atom in its ground state. I 1 + X (g) X + (g) + e - I 2 + X + (g) X 2 + (g) + e - I 3 + X 2+ (g) X 3 + (g) + e - I 1 first ionization energy I 2 second ionization energy I 3 third ionization energy 8.4 I 1 < I 2 < I 3 Ionization energy are all positive

8.4

Filled n=1 shell Filled n=2 shell Filled n=3 shell Filled n=4 shell Filled n=5 shell 8.4 Variation of the First Ionization Energy with Atomic Number A larger effective nuclear charge means a more tightly held outer electron, and hence a higher first ionization energy. He has the highest first ionization energy of all the elements.

General Trend in First Ionization Energies 8.4 Increasing First Ionization Energy

Worked Example 8.4

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) 8.5 F (g) + e - X - (g) O (g) + e - O - (g)  H = -328 kJ/mol EA = +328 kJ/mol  H = -141 kJ/mol EA = +141 kJ/mol

8.5

Variation of Electron Affinity With Atomic Number (H – Ba)

1.Which of the following statements is true? A)elements in a group have the same properties B)elements in a group have similar properties C)elements in a period have similar properties D)elements in a period have the same properties 2.A non-metal of the following is _____. A)Ba B)Fe C)P D)Cu 3.Representative elements are also called _____. A)sub-group elements B)main group elements C)non-metals D)metals 4.Which of the following is not a representative element? A)Cs B)Al C)S D)Ni

5.An element existing in the monoatomic state is _____. A)cesium B)iodine C)sulfur D)oxygen 6.An element in the tetra atomic state is ____. A)gallium B)phosphorus C)silicon D)cesium 7.The element having three valence electrons is _____. A)N B)Ge C)Al D)Ca 8.The number of valence electrons in phosphorus is _____. A)3 B)5 C)2 D)4

9.The subshell which is gradually filled in the transition metal is _____. A)s B)d C)f D)p 10.Isoelectronic ions have _____ electronic configuration. A)similar B)the same C)different D)unequal 11.O 2– is isoelectronic with _____. A)F–F– B)K+K+ C)Cl – D)Ar 12.Which of the following is not isoelectronic with Na + ? A)O 2– B)Ne C)F–F– D)K+K+

13.The element with atomic number 17 is placed in the _____ group of the IUPAC periodic table. A)7 th B)11 th C)17 th D)16 th 14.The element [Ne]3s 2 3p 3 is in the _____ group. A)13 th B)2 nd C)15 th D)17 th 15.1s 2 2s 2 2p 6 is the electronic configuration of _____. A)Cl – B)Al 3+ C)Ar D)K+K+ 16.The ion having d 10 configuration in the outermost shell is _____. A)K+K+ B)Zn 2+ C)Al 3+ D)Mg 2+

17.The metal which does not form a trivalent cation is _____. A)Fe B)Cr C)Ti D)Cd 18.The metal with the electronic configuration [Ar]3d 3 is _____. A)Cr 3+ B)Fe 3+ C)Ni 2+ D)Co The atom with the largest atomic radius of the following is _____. A)Na B)Br C)Cs D)Ca 20.The correct order of atomic radius of the following is _____. A)Na > Al > Cl > Mg B)Na < Al < Cl < Mg C)Na < Mg < Al < Cl D)Na > Mg > Al > Cl

21.The correct order of radius of the following is _____. A)O 2– < F – < Na + < Mg 2+ B)F – < O 2– < Mg 2+ < Na + C)Mg 2+ < Na + < F – < O 2– D)Mg 2+ > Na + > F – > O 2– 22.The boiling points of neon and krypton are – 245.9°C and – 152.9°C. The boiling point of argon could be A)–90°C B)–190°C C)–300°C D)–70°C 23.Pick out the correct statement from the following: A)alkali metals have the lowest ionization energy B)alkali metals have the highest ionization energy C)halogens metals have the lowest ionization energy D)inert gases metals have the lowest ionization energy 24.The element having much higher third ionization energy is _____. A)Al B)Fe C)Mg D)Tl

25.Electron affinity is the energy liberated when an atom forms a _____. A)free radiation B)cation C)anion D)molecule 26.Which of the following has the highest ionization energy? A)Cs B)Xe C)F D)He 27.The property, which decreases along a group from top to bottom, is _____. A)atomic radius B)metallic character C)ionization energy D)ionic radius

Answer Key 1-B 2-C 3-B 4-D 5-A 6-B 7-C 8-B 9-B 10-B 11-A 12-D 13-C 14-C 15-B 16-B 17-D 18-A 19-C 20-D 21-C 22-B 23-A 24-C 25-C 26-D 27-C Problems 8.5 – 8.8 – 8.12 – 8.20 – – 8.28 – 8.30 – – 8.38 – 8.40 – 8.44 – – 8.54 – 8.62 – 8.64