Mary J. Bojan Chem 110 1 Periodicity Properties of elements • Sizes of atoms and ions Electron Configuration of ions • Ionization Energy • Electron affinity • Reactivity • Metallic CharacterMary J. Bojan Chem 110 2 Electron Configuration and the Periodic Table halogens (F, Cl, Br, I) have noble gases (inert) have Valence electrons determine the chemistry! Location on Periodic Table is related to electron configuration Elements in the same row (family) have the same valence shell configuration. Example: alkali metals (row 1) have ns1 valence configuration (H) 1s1 Li [He] 2s1 Na [Ne] 3s1 K [Ar] 4s1 Rb [Kr] 5s1 Cs [Xe] 6s1Mary J. Bojan Chem 110 3 PROPERTIES OF ELEMENTS Properties of elements are determined by: • Size (n) and shape () of orbitals • Atomic number (nuclear charge) Electron configurations determine • the organization of the Periodic Table AND • the properties of the elements: reason for periodic trends in behavior Elemental properties: atomic size ionization energy electron affinities reactivityMary J. Bojan Chem 110 4 ATOMIC SIZE size decreases going from left to right across a period WHY ? • • • size increases going down group WHY ?Mary J. Bojan Chem 110 5 Trends in RadiiMary J. Bojan Chem 110 6 ELECTRON CONFIGURATIONS OF IONS e- Na Cl 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s23p5 core electrons valence electrons Elements gain or lose electrons to form separate ions with complete octets. Na+ Cl− 1s2 2s2 2p6 1s2 2s2 2p6 3s23p6 complete octets [Ne] [Ar]Mary J. Bojan Chem 110 7 Charges of Common IonsMary J. Bojan Chem 110 8 ION SIZES • anions are larger than parent atoms Cl Cl− 0.99Å 1.81Å • atom size increases going down family ion size also increases Li+ F− Na+ Cl− size K+ Br− increases Rb+ I− • cations are smaller than parent atoms Na Na+ 1.86Å 0.96ÅMary J. Bojan Chem 110 9 Ionic RadiiMary J. Bojan Chem 110 10 ISOELECTRONIC SERIES Example: O2− F− Na+ Mg2+ Al3+ # electrons? nuclear charge size Isoelectronic Isoelectronic series a series of atoms or ions that have Put these ions in order of increasing size. Ca2+ S2− K+ Cl−Mary J. Bojan Chem 110 11 IONIZATION ENERGY Energy needed to remove an electron I1 First ionization energy I1 I2 Second ionization energy I2 etc. -----------------------------------------------------Mary J. Bojan Chem 110 12 IONIZATION ENERGY Example: Mg 1s22s22p6 3s2 [Ne] valence electrons core electrons I1= 738 kJ/mol Mg+(g) [Ne] 3s1 I2= 1451 kJ/mol Mg+2(g) [Ne] I3= 7733 kJ/mol Mg+3(g) 1s2 2s22p5Mary J. Bojan Chem 110 13 IONIZATION ENERGYMary J. Bojan Chem 110 14 IONIZATION ENERGY: TRENDS going down a family I1 (kJ/mol) Li 510 Size? Na 490 I.E. K 418 increases Rb 403 Cs 375 across the periodic table Na Mg Al Si P S Cl Ar 490 735 580 780 1060 1005 1225 1550 I1 (kJ/mol) size I.E I1 increases from left to right (some exceptions) Electron further from the nucleus easier to remove, but takes extra energy to remove electrons from filled subshells (Mg, Ar) or half filled subshells (P)Mary J. Bojan Chem 110 15 Ionization EnergyMary J. Bojan Chem 110 16 Trends in I.E.Mary J. Bojan Chem 110 17 ELECTRON AFFINITIES Halogens: Group II metals (Be, Mg, Ca): Group I metals : Noble gases: Energy needed to add an electron to an atom or ion in the gas phase. Cl(g) + e− →Cl−(g) E.A. = −349kJ/molMary J. Bojan Chem 110 18 Electron AffinitiesMary J. Bojan Chem 110 19 Metal vs. NonmetalMary J. Bojan Chem 110 20 METAL REACTIVITY Li Be Na Mg K Ca Rb Sr Reactivity ____ as ionization energy ____ (IE = energy need to form a positive ion) 2Li(s) +2H2O()→2Li+(aq) +2OH−(aq)+H2(g) 2Na(s)+2H2O()→2Na+(aq)+2OH−(aq)+H2(g) 2K(s) +2H2O()→2K+(aq) +2OH−(aq)+H2(g)Mary J. Bojan Chem 110 21 HALOGEN REACTIVITY Cl2 more reactive than Br2 or I2 Br2 more reactive than I2 F2 electron Cl2 reactivity affinity Br2 I2 Reactivity increases as electron affinity increases 2KCl(aq) + Br2(aq) →no reaction 2KCl(aq) + I2(aq) →no reaction 2KBr(aq) + I2(aq) →no reaction 2KBr(aq) + Cl2(aq) →2KCl(aq) + Br2(aq) 2KI(aq) + Cl2(aq) →2KCl(aq) + I2(aq) 2KI(aq + Br2(aq) →2KBr(aq) +
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