DR Kresimir Rupnik LSU CHEMISTRY 1001 Part 9 Electrons and Photons In Chemistry-Electronic Chemical Properties (the Periodic Table)-PT 2005, Intelliome LLC, Prentice Hall

Periodic Trends in the Properties of the Elements Periodic Trends in the Properties of the Elements so, the periodic table is actually the table of electronic structure of atoms of different elements !!! Chemistry depends on the electronic structure!!!!

Prentice - Intelliome A. S. LLC Electron Configurations and the Periodic Table The periodic table can be used as a guide for electron configurations. The period number is the value of n. Groups 1A and 2A have the s-orbital filled. Groups 3A - 8A have the p-orbital filled. Groups 3B - 2B have the d-orbital filled. The lanthanides and actinides have the f-orbital filled. Note that the 3d orbital fills after the 4s orbital. Similarly, the 4f orbital fills after the 5d orbital.

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Prentice - Intelliome A. S. LLC One of the most obvious atomic property- electron structure dependence: size of the atom Start from the Electron Shells in Atoms!! As the principal quantum number increases, the size of the orbital increases.We can plot the  2 (probability of finding an electron) versus distance, r, is called a radial plot of electron density (see electronic structure Ch 3.). Atomic size varies consistently through the periodic table. Periodic Trends in atomic Properties

Prentice - Intelliome A. S. LLC Electron Shells and the Sizes of Atoms Electron Shells in Atoms The ns orbitals all have the same shape, but have different sizes and different numbers of nodes. Consider: He: 1s 2, Ne: 1s 2 2s 2 2p 6, and Ar: 1s 2 2s 2 2p 6 3s 2 3p 6. The radial electron density is the probability of finding an electron at a given distance. For He there is only one maximum (for the two 1s electrons). For Ne there are two maxima: one largely for the 1s electrons (close to the nucleus) and one largely for the n = 2 electrons (further from the nucleus). For Ar there are three maxima: one each largely for n = 1, 2, and 3.

Prentice - Intelliome A. S. LLC Electron Shells and the Sizes of Atoms Electron Shells in Atoms Consider a simple diatomic molecule. The distance between the two nuclei is called the bond distance. If the two atoms which make up the molecule are the same, then half the bond distance is called the covalent radius of the atom.

Prentice - Intelliome A. S. LLC Electron Shells and the Sizes of Atoms Atomic Sizes As the principle quantum number increases (i.e., we move down a group), the distance of the outermost electron from the nucleus becomes larger. Hence, the atomic radius increases. As we move across the periodic table, the number of core electrons remains constant. However, the nuclear charge increases. Therefore, there is an increased attraction between the nucleus and the outermost electrons. This attraction causes the atomic radius to decrease.

Prentice - Intelliome A. S. LLC Electron Shells and the Sizes of Atoms Atomic Sizes –Atomic radii (Table 4.5 textbook)

Prentice - Intelliome A. S. LLC Trends in Atomic Size either volume or radius treat atom as a hard marble Increases down a group valence shell farther from nucleus effective nuclear charge fairly close Decreases across a period (left to right) adding electrons to same valence shell effective nuclear charge increases valence shell held closer

Prentice - Intelliome A. S. LLC Trends in Atomic Size

Prentice - Intelliome A. S. LLC p + 2e - 12 p + 2e - 8e - 2e - Be (4p + & 4e - ) Group IIA Mg (12p + & 12e - ) Ca (20p + & 20e - ) 16 p + 2e - 8e - 2e - 8e -

Prentice - Intelliome A. S. LLC Li (3p + & 3e - ) Period 2 Be (4p + & 4e - )B (5p + & 5e - ) 6 p + 2e - 4e - C (6p + & 6e - ) 8 p + 2e - 6e - O (8p + & 8e - ) 10 p + 2e - 8e - Ne (10p + & 10e - ) 2e - 1e - 3 p + 2e - 4 p + 2e - 3e - 5 p +

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Prentice - Intelliome A. S. LLC Example 9.6 – Choose the Larger Atom in Each Pair C or O Li or K C or Al Se or I

Prentice - Intelliome A. S. LLC Example 9.6 – Choose the Larger Atom in Each Pair C or O Li or K C or Al Se or I?

Prentice - Intelliome A. S. LLC Property: Ionization Energy of Atoms The first ionization energy, I 1, is the amount of energy required to remove an electron from a free atom: Na(g)  Na + (g) + e -. The second ionization energy, I 2, is the energy required to remove an electron from a gaseous ion: Na + (g)  Na 2+ (g) + e -. The larger ionization energy, the more difficult it is to remove the electron. There is a sharp increase in ionization energy when a core electron is removed.

Prentice - Intelliome A. S. LLC Ionization Energy minimum energy needed to remove an electron from an atom gas state endothermic process valence electron easiest to remove M(g) + 1st IE  M 1+ (g) + 1 e - M +1 (g) + 2nd IE  M 2+ (g) + 1 e -  first ionization energy = energy to remove electron from neutral atom; 2nd IE = energy to remove from +1 ion; etc.

Prentice - Intelliome A. S. LLC Ionization Energy

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Prentice - Intelliome A. S. LLC Ionization Energy Periodic Trends in Ionization Energy Ionization energy decreases down a group. This means that the outermost electron is more readily removed as we go down a group. As the atom gets bigger, it becomes easier to remove an electron from the most spatially extended orbital. Ionization energy generally increases across a period. As we move across a period, Z eff increases. Therefore, it becomes more difficult to remove an electron. Two exceptions: removing the first p electron and removing the fourth p electron.

Prentice - Intelliome A. S. LLC Ionization Energy Periodic Trends in Ionization Energy

Prentice - Intelliome A. S. LLC Trends in Ionization Energy

Prentice - Intelliome A. S. LLC Trends in Ionization Energy as atomic radius increases, the IE generally decreases because the electron is closer to the nucleus 1st IE < 2nd IE < 3rd IE … 1st IE decreases down the group valence electron farther from nucleus 1st IE generally increases across the period effective nuclear charge increases

Prentice - Intelliome A. S. LLC Example 9.7 – Choose the Atom with the Highest Ionization Energy in Each Pair Mg or P As or Sb N or Si O or Cl

Prentice - Intelliome A. S. LLC Example 9.7 – Choose the Atom with the Highest Ionization Energy in Each Pair Mg or P As or Sb N or Si O or Cl?

Prentice - Intelliome A. S. LLC Metallic Character how well an element’s properties match the general properties of a metal Metals malleable & ductile shiny, lusterous, reflect light conduct heat and electricity most oxides basic and ionic form cations in solution lose electrons in reactions - oxidized Nonmetals brittle in solid state dull electrical and thermal insulators most oxides are acidic and molecular form anions and polyatomic anions gain electrons in reactions - reduced

Prentice - Intelliome A. S. LLC Trends in Metallic Character

Prentice - Intelliome A. S. LLC Example 9.8 – Choose the More Metallic Element in Each Pair Sn or Te Si or Sn Br or Te Se or I

Prentice - Intelliome A. S. LLC Example 9.8 – Choose the More Metallic Element in Each Pair Sn or Te Si or Sn Br or Te Se or I?

Prentice - Intelliome A. S. LLC Metals, Nonmetals, and Metalloids Metals

Prentice - Intelliome A. S. LLC Property: Electron Affinities Electron affinity is the energy change when a gaseous atom gains an electron to form a gaseous ion: Cl(g) + e -  Cl - (g) Look at electron configurations to determine whether electron affinity is positive or negative. The extra electron in Ar needs to be placed in the 4s orbital which is significantly higher in energy than the 3p orbital.

Prentice - Intelliome A. S. LLC Electron Affinities The added electron in Cl is placed in the 3p orbital to form the stable 3p 6 electron configuration.

Prentice - Intelliome A. S. LLC Properties of Main-Group Elements

Prentice - Intelliome A. S. LLC Metals, Nonmetals, and Metalloids Metals Metal character refers to the properties of metals (shiny luster, malleable and ductile, oxides form basic ionic solids, and tend to form cations in aqueous solution). Metal character increases down a group. Metal character decreases across a period. Metals have low ionization energies. Most neutral metals are oxidized rather than reduced.

Prentice - Intelliome A. S. LLC Active Metals Group 1A: The Alkali Metals Alkali metals are all soft. Chemistry dominated by the loss of their single s electron: M  M + + e - Reactivity increases as we move down the group. Alkali metals react with water to form MOH and hydrogen gas: 2M(s) + 2H 2 O(l)  2MOH(aq) + H 2 (g)

Prentice - Intelliome A. S. LLC Active Metals Group 1A: The Alkali Metals Alkali metal produce different oxides when reacting with O 2 : 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) Alkali metals emit characteristic colors when placed in a high temperature flame. The s electron is excited by the flame and emits energy when it returns to the ground state.

Prentice - Intelliome A. S. LLC Active Metals Group 1A: The Alkali Metals Na line (589 nm): 3p  3s transition Li line: 2p  2s transition K line: 4p  4s transition

Prentice - Intelliome A. S. LLC Active Metals Group 2A: The Alkaline Earth Metals Alkaline earth metals are harder and more dense than the alkali metals. The chemistry is dominated by the loss of two s electrons: M  M e -. Mg(s) + Cl 2 (g)  MgCl 2 (s) 2Mg(s) + O 2 (g)  2MgO(s) Be does not react with water. Mg will only react with steam. Ca onwards: Ca(s) + 2H 2 O(l)  Ca(OH) 2 (aq) + H 2 (g)

Prentice - Intelliome A. S. LLC Important Nonmetals Hydrogen Hydrogen is a unique element. Most often occurs as a colorless diatomic gas, H 2. It can either gain another electron to form the hydride ion, H , or lose its electron to become H + : 2Na(s) + H 2 (g)  2NaH(s) 2H 2 (g) + O 2 (g)  2H 2 O(g) H + is a proton. The aqueous chemistry of hydrogen is dominated by H + (aq).

Prentice - Intelliome A. S. LLC Important Nonmetals Group 6A: The Oxygen Group As we move down the group the metallic character increases (O 2 is a gas, Te is a metalloid, Po is a metal). There are two important forms of oxygen: O 2 and ozone, O 3. Ozone can be prepared from oxygen: 3O 2 (g)  2O 3 (g)  H = kJ. Ozone is pungent and toxic.

Prentice - Intelliome A. S. LLC Important Nonmetals Group 6A: The Oxygen Group Oxygen (or dioxygen, O 2 ) is a potent oxidizing agent since the O 2- ion has a noble gas configuration. There are two oxidation states for oxygen: 2- (e.g. H 2 O) and 1- (e.g. H 2 O 2 ). Sulfur is another important member of this group. Most common form of sulfur is yellow S 8. Sulfur tends to form S 2- in compounds (sulfides).

Prentice - Intelliome A. S. LLC Important Nonmetals Group 7A: The Halogens The chemistry of the halogens is dominated by gaining an electron to form an anion: X 2 + 2e -  2X -. Fluorine is one of the most reactive substances known: 2F 2 (g) + 2H 2 O(l)  4HF(aq) + O 2 (g)  H = kJ. All halogens consists of diatomic molecules, X 2.

Prentice - Intelliome A. S. LLC Important Nonmetals Group 7A: The Halogens Chlorine is the most industrially useful halogen. It is produced by the electrolysis of brine (NaCl): 2NaCl(aq) + 2H 2 O(l)  2NaOH(aq) + H 2 (g) + Cl 2 (g). The reaction between chorine and water produces hypochlorous acid (HOCl) which disinfects pool water: Cl 2 (g) + H 2 O(l)  HCl(aq) + HOCl(aq). Hydrogen compounds of the halogens are all strong acids with the exception of HF.

Prentice - Intelliome A. S. LLC Group 8A: The Noble Gases These are all nonmetals and monatomic. They are notoriously unreactive because they have completely filled s and p sub-shells. In 1962 the first compound of the noble gases was prepared: XeF 2, XeF 4, and XeF 6. To date the only other noble gas compound known is KrF 2.