CHAPTER 5 STUDY GUIDEJULY 6, 2010MORE ABOUT THE PERIODIC TABLE noble gases – have completely-filled valence electron shells; chemically unreactive (inert) due to filledvalence shellsATOMIC RADII (A-GROUP ELEMENTS ONLY) atomic radii – describes the relative sizes of atoms; adding more protons left to right, so the number ofelectrons determines atomic radii; the reason atomic radii decrease across a period is due to a shieldingeffect periodic trends for atomic radii: smaller/larger smaller1A 8AH 2A 3A 4A 5A 6A 7A HeLi Be B C N O F NeNa Mg 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B Al Si P S Cl ArK Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeCs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra larger example – arrange these elements in order of increasing atomic radii: Se, S, O, Te.(going down column 6A)O < S < Se < Te example – arrange these elements in order of increasing atomic radii: P, Cl, S, Si.(going across period 3)Cl < S < P < Si example – arrange these elements in order of increasing atomic radii: Ga, F, S, As.F < S < As < GaIONIZATION ENERGY1CHAPTER 5 STUDY GUIDEJULY 6, 2010 sometimes abbreviated as I.E. first ionization energy (IE 1) – the minimum amount of energy required to remove the most loosely boundelectron from an isolated gaseous atom to form a 1+ ion when an atom loses its first electron (like Mg+) atom(g) + energy ion+(g) + e- Na + energy Na+ + e- where Na has 1 unpaired electron with the electron configuration [Ne]3s1 and Na+ has0 unpaired electrons with the electron configuration [Ne] Mg(g) + 738 kJ/mol Mg+ + e- second ionization energy (IE 2) – the amount of energy required to remove the second electron from agaseous 2+ ion when an atom loses its second electron (like Mg2+) Mg, [Ne]3s2 738 kJ/mol Mg+, [Ne]3s1 1451 kJ/mol Mg2+, [Ne] ion+ + energy ion2+ + e- Mg+ + 1451 kJ/mol Mg2+ + e- IE2 > IE1 half-filled and completely-filled orbitals are more stable, so it requires more energy to remove an electron,and you destabilize the atom by adding an electron Be 2s2 takes more energy to remove this electronB 2s22p1 than to remove this electron atoms can have third, fourth, etc. ionization energies periodic trends for ionization energy: larger/smaller larger1A 8AH 2A 3A 4A 5A 6A 7A HeLi Be B C N O F NeNa Mg 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B Al Si P S Cl ArK Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeCs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra smaller ionization energy IE2 > IE1 IE1 generally increases moving from the 1A elements to the 8A elements important exceptions at Be and Mg, N and P, etc. due to filled and half-filled subshells first ionization energies of some elements: example – arrange these elements in order of increasing first ionization energies: Sr, Be, Ca, Mg.2CHAPTER 5 STUDY GUIDEJULY 6, 2010Sr < Ca < Mg < Be example – arrange these elements in order of increasing first ionization energies: Al, Cl, Na, P.Na < Al < P < Cl example – arrange these elements in order of increasing first ionization energies: B, O, Be, N.B < Be < O < NELECTRON AFFINITY electron affinity – the amount of energy absorbed when an electron is added to an isolated gaseous atom toform an ion with a 1- charge sign conventions: if electron affinity > 0 (+), then energy is absorbed if electron affinity < 0 (–), then energy is released electron affinity is essentially a measure of an atom’s ability to form negative ions atom(g) + e- + EA ion-(g) Mg(g) + e- + 231 kJ/mol Mg-(g)EA = +231 kJ/mol (endothermic reaction) Br(g) + e- Br-(g) + 323 kJ/molEA = -323 kJ/mol (exothermic reaction) periodic trends for electron affinity: smaller/larger smaller1A 8AH 2A 3A 4A 5A 6A 7A HeLi Be B C N O F NeNa Mg 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B Al Si P S Cl ArK Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeCs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra larger exceptions for filled and half-filled subshells Be 2s2 filled EA ~ 0N 2p3 half-filled EA = 0 electron affinity values of some elements: example – arrange these elements in order of increasing electron affinities: Al, Mg, Si, Na.3CHAPTER 5 STUDY GUIDEJULY 6, 2010Si < Na < Al < Mg(Na is bizarre in this instance; otherwise, would have been Si < Al < Na < Mg) Na atom vs. Na+ ion Na atom [Ne]3s1 ) ) )e- Na+ ion [Ne] ) )e-IONIC RADII cations (positive ions) are always smaller than their respective neutral atoms cation (positive ion) radii decrease going from left to right across a period increasing nuclear charge attracts the electrons and decreases the ionic radius anions (negative ions) are always larger than their neutral atoms anion (negative ion) radii decrease going from left to right across a period increasing electron numbers in highly-charged ions cause the electrons to repel and increasethe ionic radius periodic trends for ionic radii: smaller/larger smaller1A 8AH 2A 3A 4A 5A 6A 7A HeLi Be B C N O F NeNa Mg 3B 4B 5B 6B 7B 8B 8B 8B 1B 2B Al Si P S Cl ArK Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br KrRb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I XeCs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At RnFr Ra larger except it’s more like this:(Na+) (Mg2+) (Al3+) … (N3-) (O2-) (F-) more electrons fighting for fewer protons causes repulsion 7N3-7 p+10 e- ) ) - 8O2-8 p+10 e- ) ) 2- 9F-9 p+10 e- ) ) ) 3- example – arrange these elements in order of decreasing ionic radii: Ga, K, Ca.K+ > Ca2+ > Ga3+ example – arrange these elements in order of increasing ionic radii: Cl, Se, Br, S.Cl- < S2- < Br- < Se2-Cl = period 3; S = period 3; Br = period 4; Se = period 4ELECTRONEGATIVITY electronegativity – a measure of the relative tendency of an atom to attract electrons to itself whenchemically combined with another element the higher the number, the more they are attracted to each other numbers range …
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