Periodic Properties of the Elements. Chapter 7

Transcription

1 Periodic Properties of the Elements Chapter 7

2 The Sizes of Atoms The bond distance: d The covalent radius of the atom Non-bonding atomic radius

3 Atomic size varies consistently through the periodic table.

4 Atomic size varies consistently through the periodic table.

5 The larger ionization energy, the more difficult it is to remove the electron. Ionization Energy Ionization energy: the minimum energy (kj/mol) required to remove an electron from the ground state of a gaseous atom or ion. The first ionization energy(i 1 ): Na (g) Na + (g) + e - The second ionization energy(i 2 ): Na + (g) Na 2+ (g) + e - I 1 < I 2 < I 3 The third ionization energy(i 3 ): Na 2+ (g) Na 3+ (g) + e-

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7 Periodic Trends in Ionization Energy

8 Filled n=1 shell Filled n=2 shell Filled n=3 shell Filled n=4 shell Filled n=5 shell

9 Electron Affinities Electron Affinity: 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 - F - (g) O (g) + e - O - (g) EA = -328 kj/mol EA = -141 kj/mol

10 Electron Affinities Electron affinities Ionization Energy Atom(g) + e - Ion(g) E electron affinity Atom (g) Ion (g) + e I Ionization energy 1 - Cl(g) + e Exothermic Electron affinities Endothermic Cl (g) - E - Ar(g) + e - + Ar (g) - E -

11 Electron Affinities The more negative the electron affinity, the greater the attraction of the atom to an electron

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13 Ion Radii

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15 Metals, Nonmetals, and Metalloids

16 Metals, Nonmetals, and Metalloids Metals Metallic character increases down a group. Metallic character decreases across a period. Metals have low ionization energies. Most neutral metals are oxidized rather than reduced. 2 Cu( s) + O 2 Cu O( s) Ni( s) + O 2 NiO( s) 2

17 Metals, Nonmetals, and Metalloids Metals When metals are oxidized they tend to form characteristics cations. All group 1A metals form M + ions. All group 2A metals form M 2+ ions. Most transition metals have variable charges.

18 Metals, Nonmetals, and Metalloids

19 Metals, Nonmetals, and Metalloids Nonmetals: Metal + nonmetal salt 2Al(s) + 3Br 2 (l) 2AlBr 3 (s) Metalloids: Metalloids have properties that are intermediate between metals and nonmetals.

20 Metals, Nonmetals, and Metalloids Metalloids Example: Si (shown here) has a metallic luster but it is brittle. Metalloids have found fame in the semiconductor industry. Sliced thin wafer of large silicon crystals

21 Metals, Nonmetals, and Metalloids Group 1A: The Alkali Metals + M M + e Reactivity increases as we move down the group 1) Alkali metals + water MOH + hydrogen gas 2 M ( s) + 2 H O( l) 2 MOH( aq) + H ( g) 2 2

22 Metals, Nonmetals, and Metalloids Group 1A: The Alkali Metals 2) Alkali metal + O 2 different oxides 4Li(s) + O 2 (g) 2Li 2 O(s) (oxide) 2Na(s) + O 2 (g) Na 2 O 2 (s) (peroxide)( ) K(s) + O 2 (g) KO 2 (s) (superoxide)( )

23 Group Trends for the Active Metals Group 1A: The Alkali Metals Li line: 2p 2s transition Na line (589 nm): 3p 3s transition K line: 4p 4s transition 3) Alkali metals emit characteristic colors when placed in a high temperature flame.

24 Group Trends for the Active Metals Group 2A: The Alkaline Earth Metals 1) Alkaline earth metals are harder and more dense than the alkali metals. 2 M M + + 2e Mg(s) + Cl 2 (g) MgCl 2 (s) 2Mg(s) + O 2 (g) 2MgO(s) 2) 2 M( s) + 2 H O( l) 2 Be does not react with water. Mg will only react with steam. Ca(s) + 2H 2 O(l) Ca(OH) 2 (aq) + H 2 (g)

25 Group Trends for Selected Nonmetals Hydrogen 1) To gain another electron to form the hydride ion H : 2Na(s) + H 2 (g) 2NaH(s) 2) To lose its electron to become H + : 2H 2 (g) + O 2 (g) 2H 2 O(g) 3) H + is a proton The aqueous chemistry of hydrogen is dominated by H + (aq).

26 Group Trends for Selected Nonmetals Group 6A: The Oxygen Group move down the group the metallic character increases O 2 : a gas, Te : a metalloid, Po : a metal Two important forms of oxygen: O 2 and O 3 (ozone) 3O 2 (g) 2O 3 (g) H = kj. Ozone: pungent and toxic.

27 Group Trends for Selected Nonmetals Group 6A: The Oxygen Group Oxygen : a potent oxidizing agent ( O 2- ion : a noble gas configuration) Two oxidation states for oxygen: 2 - (e.g. H 2 O) and 1 - (e.g. H 2 O 2 ) Most common form of sulfur: yellow S 8 Sulfur tends to form S 2- in compounds (sulfides) Ag2 S, CuS, HgS

28 Group Trends for Selected Nonmetals Group 7A: The Halogens X 2 + 2e - 2X - Fluorine : one of the most reactive substances known 2F 2 (g) + 2H 2 O(l) 4HF(aq) + O 2 (g) H = kj. F2, Cl2, Br2, I 2

29 Group Trends for Selected Nonmetals Group 7A: The Halogens Chlorine: the most industrially useful halogen produced by the electrolysis of brine (NaCl): 2 NaCl( aq) + 2 H O( l) 2 NaOH ( aq) + H ( g) + Cl( g) Cl ( g) + H O( l) = HClaq ( ) + HOCl( aq) hypochlorous acid Disinfects pool water Hydrogen compounds of the halogens are all strong acids with the exception of HF.

30 Group Trends for Selected Nonmetals Group 8A: The Noble Gases (ns 2 np 6, n 2) 1) Nonmetals and monatomic. 2) Notoriously unreactive (completely filled s and p sub-shells) 3) The first compound of the noble gases was prepared in 1962 : XeF2, XeF4, XeF6 4) To date the only other noble gas compound: KrF 2