CHAPTER 8C Periodic Relationships Among the Elements Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 1

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 - F - (g) O (g) + e - O - (g)  H = -328 kJ/mol EA = +328 kJ/mol  H = -141 kJ/mol EA = +141 kJ/mol 2

Electron affinity Energy released or absorbed when an electron is added to a gaseous atom or ion in the ground state: X (g) + 1e - → X - (g) usually exothermic process If removing an electron is endothermic, then the reversed process is exothermic e - 7e - e - F (g) + 1e - → F - (g)  H=-328 kJ/mol II/

Electron attracted to nucleus The higher the charge exerted by nucleus (effective nuclear charge, Z eff ) The closer the electron is to nucleus (smaller r)  F (attraction) larger  Potential energy of electron and atom strongly reduced  Released energy larger  More negative electron affinity F (g) + 1e - F - (g) O (g) + 1e - O - (g) -328 kJ/mol -141 kJ/mol E potential Second E.A always endothermic: O - (g) + 1e - → O 2- (g)  H > 0 II/

8.5 5 Exceptions A)Group 2A (ns 2 ) lower than 1A (ns 1 ) in the same period B) Group 5A (ns 2 np 3 ) lower than 4A (ns 2 np 2 ) in the same period increase

8.5 Variation of Electron Affinity With Atomic Number (H – Ba) 6

smaller Larger Size Atomic Radiuses Larger Ionization energy smaller Larger Electron Affinity smaller

Halogens (group 7A, F to At) Most negative EA values, addition of an e - leads to noble gas configuration, very favorable. Group 5A (N to Bi) ½ filled shell discourages addition of an electron, EA values less negative than neighbors (groups 4A & 6A). Alkaline Earths (group 2A, Be to Ba) Filled s subshell discourages addition of an electron, EA values nearly zero. Noble Gases (Group 8A, He to Rn) Completely filled shell strongly discourages addition of an electron, EA values are positive. 3 rd period more negative than 2 nd period atoms are larger, more space for the electrons, repulsion between electrons less, more favorable e - 7e - 2e - 8e e - EA (Cl)=-348 kJ/mol EA (F)=-328 kJ/mol II/

Electronegativity: the ability of an atom to attract toward it self to the electron in achemical bond. السالبية الكهربية:- هي قدرة الذرة على جذب إلكترونات الرابطة الكيميائية

Electronegativity Indicates the attraction of an atom for shared electrons. Increases from left to right going across a period on the periodic table. Decreases going down a group on the periodic table. Is high for the nonmetals with fluorine as thehighest. Is low for the metals. فى الدورة الأفقية:- تزداد السالبية الكهربية إذا اتجهنا من اليسار إلى اليمين أى بزيادة العدد الذرى ونقص نصف القطروهذا يؤدى إلى زيادة قوة جذب النواة لإلكترونات الرابطة. فى المجموعة الرأسية:- تقل السالبية الكهربية من أعلى إلى أسفل أى بزيادة العدد الذرى وزيادة نصف القطر. وهذا يؤدى إلى نقص قوة جذب النواة لإلكترونات الرابطة. ملاحظات:- الفلور يعتبر أكبر العناصر سالبية كهربية. الفرق فى السالبية الكهربية للعناصر له دور فى تحديد نوع الرابطة بين الذرات. الفلزات لها أقل سالبية لكبر نصف قطرها. اللافلزات لها أكبر سالبية لصغر نصف قطرها.

Electronegativity ++ –– 00 00 HClHH

Electronegativity When electrons are shared by two atoms a covalent bond is formed. When the atoms are the same they pull on the electrons equally. Example, H-H. When the atoms are different, the atoms pull on the electrons unevenly. Example, HCl

Trends in Electronegativity Electronegativity generally decreases as you move down a group. Electronegativity of the representative elements (Group A elements) increases as you move across a period.

Electronegativities of Some Elements Element Pauling scale F 4.0 Cl 3.0 O 3.5 N 3.0 S 2.5 C 2.5 H 2.1 Na 0.9 Cs0.7

9.5 The Electronegativities of Common Elements

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 * 16

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 17

9.The subshell which is gradually filled in the transition metal is _____. A)s B)d *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 – * 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 + * 18

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+ 19

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 * 20

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 21

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 22

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 –