Section 5.3 Periodicity Trends Objectives: To state the trend in atomic size within a group or period of elements. To state the trend in metallic character within a group or period.

PERIODICITY -based upon -trend in properties of element across a “period” & within a “group” -based upon 1) Effective Nuclear Charge (ENC) - ENC = # protons - # core (kernal / inner) electrons - aka: Coulombic Attraction - attraction between (+) & (-) charges - based upon 1) Amount of CHARGE 2) Distance Across the period, ENC INCREASES due increase # p+ & e- Objectives: To state the trend in atomic size within a group or period of elements. To state the trend in metallic character within a group or period.

Coulombic Attraction opposites attract like repels 2) Distance Based upon….. 1) Amount of Charge opposites attract like repels 2) Distance between charges A 1+ 1- 2+ 2- B 2+ 2- C

+ 2) Shielding Effect - - - - nucleus Electron Shield Valence Across a period, , shielding effect CONSTANT Why? SAME ENERGY LEVEL (distance) Valence + - nucleus - - Within a group, shielding effect INCREASES due to INCREASE ENERGY LEVELS (distance) Electrons - Electron Shield “kernel” (Inner or Core) electrons Kernel electrons block the attractive force of the nucleus from the valence electrons

Atomic Radius:the size of a NEUTRAL atom- Across the period, atomic radius decreases because there is an increase in nuclear charge and Effective Nuclear Charge (# protons – # core electrons). As the attraction between the (+) nucleus and the (–) valence electrons , the atomic size . Greater coulombic attraction. Each valence electron is pulled by the full ENC Within a group/family, atomic radius INCREASES Why? Increase SHIELDING Li Be B 1s22s1 1s22s2 1s22s22p1 (ENC = 1) (ENC = 2) (ENC = 3) Li Be B + + + + + + + + + + + +

Atomic Radii Within a group/family: atomic radius INCREASES because of INCREASE SHIELDING LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 175

Atomic Radius Example: Place the following elements in order from smallest to largest atomic radius & explain why? C, O, Sn, Sr ANSWER: O < C < Sn < Sr O < C …Increase ENC with “O” C < Sn…Increase SHIELDING with “Sn” Sn < Sr…Increase ENC with “Sn” 7

Ionization Energy (IE): the energy required to remove an e– from an atom Across the period, ionization energy INCREASES, due to increase ENC. Within a group, ionization energy DECREASES, due to increase SHIELDING. M + 1st I.E. M1+ + e– removes 1st e– M1+ + 2nd I.E. M2+ + e– M2+ + 3rd I.E. M3+ + e– Each successive ionization requires more energy than the previous one Why? Increase Positive Charge (stronger pull from the nucleus) 8

Ionization Energies (kJ/mol) Element Na Mg Al Si P S Cl Ar 1st 498 736 577 787 1063 1000 1255 1519 2nd 4560 1445 1815 1575 1890 2260 2295 2665 3rd 6910 7730 2740 3220 2905 3375 3850 3945 4th 9540 10,600 11,600 4350 4950 4565 5160 5770 5th 13,400 13,600 15,000 16,100 6270 6950 6560 7320 6th 16,600 18,000 18,310 19,800 21,200 8490 9360 8780 Ionization energy increases with the removal of each additional electron. Metals have low ionization energy; nonmetals have high ionization energy. This experimental data gives evidence for: 1) effect of increasing nuclear charge 2) stability of octet 3) effect of increased radius 4) s & p sublevel in outer level SUGGESTION: Emphasize that theories came from experimental evidence! Herron, Frank, Sarquis, Sarquis, Cchrader, Kulka, Chemistry 1996, Heath, page Shaded area on table denotes core electrons. 9

Ionization Energy Example: Place the following elements in order from smallest to largest 1st IE & explain why? Al, Ar, Cs, Na ANSWER: Cs < Na < Al < Ar Cs < Na …Increase SHIELDING with “Cs” Na < Al …Increase ENC with “Al” Al < Ar…Increase ENC with “Ar” 10

First Ionization energy He Helium (He) has… a greater IE than H same shielding greater nuclear charge n H First Ionization energy He H 1+ 2+ 1e- 2e- Atomic number

First Ionization energy He Li has… lower IE than H more shielding Further away outweighs greater nuclear charge n H First Ionization energy Li Atomic number

First Ionization energy He Helium (He) has… a greater IE than H same shielding greater nuclear charge n H First Ionization energy He H 1+ 2+ 1e- 2e- Atomic number

First Ionization energy He Li has… lower IE than H more shielding Further away outweighs greater nuclear charge n H First Ionization energy Li Atomic number

First Ionization energy He Be has higher IE than Li same shielding greater nuclear charge n 1e- 2e- 3+ 4+ H 3+ 4+ 2e- 1e- First Ionization energy Be Be Li Li Atomic number

First Ionization energy He B has lower IE than Be same shielding greater nuclear charge p-orbitals available n 2e- 4+ 3e- 5+ 4+ 5+ 2e- 3e- H First Ionization energy Be B Be B Li 2s 2p 1s Atomic number

First Ionization energy He n H First Ionization energy C Be B Li 2s 2p 1s Atomic number

First Ionization energy He n N H First Ionization energy C Be B Li 2s 2p 1s Atomic number

First Ionization energy He n N Breaks the pattern because removing an electron gets to ½ filled p-orbital H O First Ionization energy C Be B Li 2s 2p 1s Atomic number

First Ionization energy He n F N H O First Ionization energy C Be B Li 2s 2p 1s Atomic number

First Ionization energy He Ne n F N Ne has a lower IE than He Both are full energy levels, Ne has more shielding Greater distance H O First Ionization energy C Be B Li 2s 2p 1s Atomic number

First Ionization energy H He Li Be B C N O F Ne Na n Na has a lower IE than Li Both are s1 Na has more shielding Greater distance First Ionization energy 2s 2p 1s 3s Atomic number

Ionization Energy Example: Why does magnesium, phosphorus and zinc exhibit slightly higher ionization energies than the general trend within each of their period? ANSWER: Irregularities occur with half filled & filled sublevels, because filled & half-filled sublevels are more stable. 23

Ionic Radius: the size of an ion ( + or – charged atom) Metals Nonmetals Cations are smaller than parent atoms Anions are larger than parent atoms Al 143 50 e Group 13 Group 1 Group 17 e e 152 186 227 Li Na K 60 Li+ F- 136 F Cl Br 64 99 114 e e 95 Na+ Cl- 181 Al3+ e e 133 K+ Br- 195

The Octet Rule and Common Ions 8+ - 9+ 11+ 12+ 10+ - Oxygen atom O 1s22s22p4 Fluorine atom F 1s22s22p5 Neon atom Ne 1s22s22p6 Sodium atom Na 1s22s22p63s1 Magnesium atom Mg 1s22s22p63s2 +2e- +1e- -1e- -2e- 8+ - 9+ - 11+ - 12+ - Oxygen ion O2- 1s22s22p6 Fluorine ion F1- 1s22s22p6 Sodium ion Na1+ 1s22s22p6 Magnesium ion Mg2+ 1s22s22p6

Isoelectronic Species Isoelectronic – different element with the same number of electrons. p = 8 n = 8 e = 10 p = 9 n = 9 e = 10 p = 10 n = 10 e = 10 p = 11 n = 11 e = 10 p = 12 n = 12 e = 10 8+ - 9+ - 10+ - 11+ - 12+ - Oxygen ion O2- 1s22s22p6 Fluorine ion F1- 1s22s22p6 Neon atom Ne 1s22s22p6 Sodium ion Na1+ 1s22s22p6 Magnesium ion Mg2+ 1s22s22p6 Can you come up with another isoelectronic series of five elements?

Oxidation Number: most common ION it will form 1 8 Groups 2 3 4 5 6 7 Li1+ Be2+ F1- O2- Cl1- Na1+ Mg2+ Al3+ S2- Br1- K1+ Ca2+ Zn2+ Ga3+ Se2- I1- Rb1+ Sr2+ Ag1+ In3+ Te2- Many elements have a tendency to gain or lose enough electrons to attain the same number of electrons as the noble gas closest to them in the periodic table. Monatomic ions contain only a single atom. Charges of most monatomic ions derived from the main group elements are predicted by simply looking at the periodic table and counting how many columns an element lies from the extreme left or right. Transition metals form cations with various charges. Cs1+ Ba2+ Group 1: 1+ Group 16: 2- Group 2: 2+ Group 17: 1- 27

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What is “PERIODICITY”? Periodicity is predictable repeating patterns/trends on the periodic table. Objectives: To state the trend in atomic size within a group or period of elements. To state the trend in metallic character within a group or period. 29

What is “PERIODICITY” based upon? 1) EFFECTIVE NUCLEAR CHARGE - ENC = # protons - # core (kernal / inner) electrons - attraction between (+) & (-) charges - deals with 1) Amount of CHARGE 2) DISTANCE between charges - Across the period, ENC INCREASES due increase # p+ & e- 2) SHIELDING EFFECT - Kernel (core / inner) electrons block the attractive force of the nucleus from the valence electrons - Across a period, shielding effect CONSTANT Why? SAME ENERGY LEVEL (distance) - Within a group, shielding effect INCREASES Due to INCREASE ENERGY LEVELS (distance) Objectives: To state the trend in atomic size within a group or period of elements. To state the trend in metallic character within a group or period. 30

1st Ionization Energies (KJ/mol) Why are their “dips” in the 1st IE for Be and N? Irregularities occur with filled & half-filled sublevels because they are more stable.

Why is there are huge jump between the 2nd IE & the 3rd IE for Mg? 2nd IE = Mg+2 which looks like the noble gas [Ne] It take a lot of energy to break a noble gas configuration.

Electronegativity A measure ability of an atom in a chemical compound to attract electrons Across a period, EN’s INCREASE WHY? Increase Nuclear Charge Within a group/family, EN’s DECREASE or remain the same WHY? Increase Shielding

Electronegativities Period H B P As Se Ru Rh Pd Te Os Ir Pt Au Po At 2.1 B 2.0 P As Se 2.4 Ru 2.2 Rh Pd Te Os Ir Pt Au Po At 2.0 - 2.4 1 1 2A 3A 4A 5A 6A 7A Actinides: 1.3 - 1.5 Li 1.0 Ca Sc 1.3 Sr Y 1.2 Zr 1.4 Hf Mg La 1.1 Ac 1.0 - 1.4 Lanthanides: 1.1 - 1.3 * y Be 1.5 Al Si 1.8 Ti V 1.6 Cr Mn Fe Co Ni Cu 1.9 Zn 1.7 Ga Ge Nb Mo Tc Ag Cd In Sn Sb Ta W Re Hg Tl Pb Bi 1.5 - 1.9 C 2.5 S Br 2.8 I 2.5 - 2.9 N 3.0 O 3.5 F 4.0 Cl 3.0 - 4.0 2 2 Na 0.9 K 0.8 Rb Cs 0.7 Ba Fr Ra Below 1.0 3 3 3B 4B 5B 6B 7B 8B 1B 2B Period 4 4 5 5 6 6 Linus Pauling (1901 - 1994) awarded Nobel Prize in chemistry in 1954 for his 1939 text, The Nature of the Chemical Bond, and also won the Nobel Peace Prize in 1962 for his fight to control nuclear weapons. The greater the electronegativity of an atom in a molecule, the more strongly it attracts the electrons in a covalent bond. 7

Across a period, electron affinity INCREASES Electron Affinity - the energy change associated with the addition of an electron Across a period, electron affinity INCREASES WHY? Increase Effective Nuclear Charge (ENC) with Constant Shielding Within a group/family, electron affinity DECREASES WHY? Increase SHIELDING effect (Slight Increase ENC – but Shielding predominates) NOTE: BACKWARD SCALE SMALL NEGATIVE # LARGE NEGATIVE # NOTE:Irregularities due to repulsive forces in the relatively small p orbitals.

Table of Electron Affinities

Summary of Periodic Trends Shielding is constant Atomic radius decreases Ionization energy increases Electronegativity increases Nuclear charge increases 1A Ionization energy decreases Electronegativity decreases Nuclear charge increases Atomic radius increases Shielding increases Ionic size increases 2A 3A 4A 5A 6A 7A Ionic size (cations) Ionic size (anions) decreases decreases

Melting Points H He Mg Symbol Melting point oC Li Be B C N O F Ne -259.2 He -269.7 1 1 Mg 650 Symbol Melting point oC Li 180.5 Be 1283 B 2027 C 4100 N -210.1 O -218.8 F -219.6 Ne -248.6 2 2 > 3000 oC 2000 - 3000 oC Na 98 Mg 650 Al 660 Si 1423 P 44.2 S 119 Cl -101 Ar -189.6 3 3 K 63.2 Ca 850 Sc 1423 Ti 1677 V 1917 Cr 1900 Mn 1244 Fe 1539 Co 1495 Ni 1455 Cu 1083 Zn 420 Ga 29.78 Ge 960 As 817 Se 217.4 Br -7.2 Kr -157.2 4 4 Rb 38.8 Sr 770 Y 1500 Zr 1852 Nb 2487 Mo 2610 Tc 2127 Ru 2427 Rh 1966 Pd 1550 Ag 961 Cd 321 In 156.2 Sn 231.9 Sb 630.5 Te 450 I 113.6 Xe -111.9 5 5 Cs 28.6 Ba 710 La 920 Hf 2222 Ta 2997 W 3380 Re 3180 Os 2727 Ir 2454 Pt 1769 Au 1063 Hg -38.9 Tl 303.6 Pb 327.4 Bi 271.3 Po 254 At Rn -71 6 6 Ralph A. Burns, Fundamentals of Chemistry , 1999, page 1999

Densities of Elements H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K 0.071 He 0.126 1 1 Li 0.53 Be 1.8 B 2.5 C 2.26 N 0.81 O 1.14 F 1.11 Ne 1.204 2 2 Na 0.97 Mg 1.74 Al 2.70 Si 2.4 P 1.82w S 2.07 Cl 1.557 Ar 1.402 3 3 K 0.86 Ca 1.55 Sc (2.5) Ti 4.5 V 5.96 Cr 7.1 Mn 7.4 Fe 7.86 Co 8.9 Ni 8.90 Cu 8.92 Zn 7.14 Ga 5.91 Ge 5.36 As 5,7 Se 4.7 Br 3.119 Kr 2.6 4 4 Rb 1.53 Sr 2.6 Y 5.51 Zr 6.4 Nb 8.4 Mo 10.2 Tc 11.5 Ru 12.5 Rh 12.5 Pd 12.0 Ag 10.5 Cd 8.6 In 7.3 Sn 7.3 Sb 6.7 Te 6.1 I 4.93 Xe 3.06 5 5 Cs 1.90 Ba 3.5 La 6.7 Hf 13.1 Ta 16.6 W 19.3 Re 21.4 Os 22.48 Ir 22.4 Pt 21.45 Au 19.3 Hg 13.55 Tl 11.85 Pb 11.34 Bi 9.8 Po 9.4 At --- Rn 4.4 6 6 Element Year Discovered Density (g/cm3) Osmium 1804 22.59 Iridium 1804 22.56 Platinum 1784 21.45 Rhenium 1925 21.01 Neptunium 1940 20.47 Plutonium 1940 20.26 Gold prehistoric 19.32 Tungsten 1783 19.26 Uranium 1789 19.05 Tantalum 1802 16.67 8.0 – 11.9 g/cm3 12.0 – 17.9 g/cm3 > 18.0 g/cm3 Mg 1.74 Symbol Density in g/cm3C, for gases, in g/L W