Dr. Chris Kozak Memorial University of Newfoundland, Canada. Contents

Transcription

1 General Chemistry Principles and Modern Applications Petrucci Harwood Herring 9 th Edition Chapter 9: The Periodic Table and Some Atomic Properties Dr. Chris Kozak Memorial University of Newfoundland, Canada Contents 9-1 Classifying the Elements: The Periodic Law and the Periodic Table 9-2 Metals and Nonmetals and Their Ions 9-3 The Sizes of Atoms and Ions 9-4 Ionization Energy 9-5 Electron Affinity 9-6 Magnetic Properties 9-7 Periodic Properties of the Elements Slide 2

2 9-1 Classifying the Elements: The Periodic Law and the Periodic Table 1869, Dimitri Mendeleev Lother Meyer When the elements are arranged in order of increasing atomic mass, certain sets of properties recur periodically. Slide 3 Periodic Law Slide 4

3 Mendeleev s Periodic Table 1871 = 44 = 68 = 72 = 100 Slide 5 Predicted Elements were Found 9.1 Slide 6

4 X-Ray Spectra Moseley 1913 X-ray emission is explained in terms of transitions in which e - drop into orbits close to the atomic nucleus. Correlated frequencies to nuclear charges. ν = A (Z b) 2 Used to predict new elements (43, 61, 75) later discovered. Slide 7 Alkali Metals The Periodic table Noble Gases Alkaline Earths Halogens Main Group Pnictogens Transition Metals Main Group Lanthanides and Actinides Chalcogens Slide 8

5 9-2 Metals, Nonmetals and Their Ions Metals Good conductors of heat and electricity. Malleable and ductile. Moderate to high melting points. Nonmetals Nonconductors of heat and electricity. Brittle solids. Some are gases at room temperature. Slide 9 Metals Tend to Lose Electrons Metals are usually oxidized (weakly held valence electrons) Slide 10

6 Nonmetals Tend to Gain Electrons Non-metals gain electrons (more difficult to oxidize than metals) Slide The Sizes of Atoms and Ions Overlap of electron density (sharing of electrons in a covalent bond) About ½ distance between nuclei No formal overlap of electron density About ½ distance between nuclei in a crystalline solid metal No overlap of electron density, since e - are shared unevenly Difficult to predict without more examples Slide 12

7 Atomic Radius Slide 13 Trends in Atomic Radii Sizes of atoms increase down a group. Why? Radii decrease across a period in the main group. Why? Radii in Transition metals remain fairly constant except for a few spikes. Why? Electrons go into an inner shell, thus participate in shielding the outer shell electrons from the increasing Z eff. Remember, in atoms in the ground state, 3d is higher in E, but is in fact closer to the nucleus (n = 3 in 3d, n = 4 in 4s). Slide 14

8 Screening and Penetration Z eff = Z S Z 2 E n = -R eff H n 2 Slide 15 Cationic Radii Slide 16

9 Anionic Radii Slide 17 Atomic and Ionic Radii Slide 18

10 SAMPLE PROBLEM: Ranking Elements by Atomic Size PROBLEM: SOLUTION: Using only the periodic table rank each set of main group elements in order of decreasing atomic size: (a) Ca, Mg, Sr (b) K, Ga, Ca (c) Br, Rb, Kr (d) Sr, Ca, Rb PLAN: Elements in the same group increase in size you go down; elements decrease in size as you go across a period. (a) Sr > Ca > Mg These elements are in Group 2. (b) K > Ca > Ga These elements are in Period 4. (c) Rb > Br > Kr (d) Rb > Sr > Ca Rb has a higher energy level and is far to the left. Br is to the left of Kr. Ca is one energy level smaller than Rb and Sr. Rb is to the left of Sr. Slide 19 SAMPLE PROBLEM: Ranking Ions by Size PROBLEM: Rank each set of ions in order of decreasing size, and explain your ranking: (a) Ca 2+, Sr 2+, Mg 2+ (b) K +, S 2-, Cl - (c) Au +, Au 3+ PLAN: Compare positions in the periodic table, formation of positive and negative ions and changes in size due to gain or loss of electrons. SOLUTION: (a) Sr 2+ > Ca 2+ > Mg 2+ These are members of the same Group 2 and therefore decrease in size going up the group. (b) S 2- > Cl - > K + The ions are isoelectronic; S 2- has the smallest Z eff and therefore is the largest while K + is a cation with a large Z eff and is the smallest. (c) Au + > Au 3+ The higher the + charge, the smaller the ion. Slide 20

11 9-4 Ionization Energy Mg(g) Mg + (g) + e - I 1 = 738 kj Mg + (g) Mg 2+ (g) + e - I 2 = 1451 kj Z 2 I = R eff H n 2 Slide 21 The trend in acid-base behavior of element oxides. Slide 22

12 First Ionization Energy Slide I 2 (Mg) vs. I 3 (Mg) I 1 (Mg) vs. I 1 (Al) I 1 (P) vs. I 1 (S) Slide 24

13 SAMPLE PROBLEM: Ranking Elements by First Ionization Energy PROBLEM: Using the periodic table only, rank the elements in each of the following sets in order of decreasing IE 1 : (a) Kr, He, Ar (b) Sb, Te, Sn (c) K, Ca, Rb (d) I, Xe, Cs PLAN: IE decreases as you proceed down in a group; IE increases as you go across a period. SOLUTION: (a) He > Ar > Kr (b) Te > Sb > Sn (c) Ca > K > Rb (d) Xe > I > Cs Group 18 - IE decreases down a group. Period 5 elements - IE increases across a period. Ca is to the right of K; Rb is below K. I is to the left of Xe; Cs is further to the left and down one period. Slide Electron Affinity F(g) + e - F - (g) EA = -328 kj F(1s 2 2s 2 2p 5 ) + e - F - (1s 2 2s 2 2p 6 ) Li(g) + e - Li - (g) EA = kj Slide 26

14 First Electron Affinities Slide 27 Second Electron Affinities O(g) + e - O - (g) EA = -141 kj/mol O - (g) + e - O 2- (g) EA = +744 kj/mol Slide 28

15 9-6 Magnetic Properties Diamagnetic atoms or ions: All e - are paired. Weakly repelled by a magnetic field. Paramagnetic atoms or ions: Unpaired e -. Attracted to an external magnetic field. Slide 29 Paramagnetism Slide 30

16 Apparatus for measuring the magnetic behavior of a sample: The Gouy Balance Slide Periodic Properties of the Elements Slide 32

17 Trends in the Periodic Table Slide 33 Boiling Point ? 332? Slide 34

18 Melting Points of Elements Slide 35 Melting Points of Compounds 9.6 Slide 36

19 Reducing Ability of Group 1 and 2 Metals 2 K(s) + 2 H 2 O(l) 2 K OH - + H 2 (g) I 1 = 419 kj I 1 = 590 kj I 2 = 1145 kj Ca(s) + 2 H 2 O(l) Ca OH - + H 2 (g) Slide 37 Oxidizing Abilities of the Halogens 2 Na + Cl 2 2 NaCl Cl I - 2 Cl - + I 2 Slide 38

20 Acid-Base Nature of Element Oxides Basic oxides (base anhydrides): Li 2 O(s) + H 2 O(l) 2 Li + (aq) + 2 OH - (aq) Acidic oxides (acid anhydrides): SO 2 (g) + H 2 O(l) H 2 SO 3 (aq) Na 2 O and MgO yield basic solutions Cl 2 O, SO 2 and P 4 O 10 yield acidic solutions SiO 2 insoluble in water but dissolves in strong base, acidic oxide In aqueous solutions: Metal Oxides are basic Non-metal Oxides are acidic Slide 39