Building Atoms - Period 3 Na 1s22s22p63s1 [Ne]3s1 Mg 1s22s22p63s2 [Ne]3s2 Al 1s22s22p63s23p1 [Ne]3s23p1 Si 1s22s22p63s23p2 [Ne]3s23p2 P 1s22s22p63s23p3 [Ne]3s23p3 S 1s22s22p63s23p4 [Ne]3s23p4 Cl 1s22s22p63s23p5 [Ne]3s23p5 Ar 1s22s22p63s23p6 [Ne]3s23p6 1 Building Atoms - Period 4 K Ca Sc – 4p or 3d ? 2 Building Atoms - Period 4 Ti V Cr Half-filled or completely filled subshells exhibit additional stability 3 Building Atoms - Period 4 Mn Ni Fe Cu Co Zn Elements for which the d-orbitals are being filled are called transition metals Sc through Zn: 1st row transition metals 4 Building Atoms - Period 4 Ga Se Ge Br As Kr 5 Building Atoms - Period 5 Rb Mo Sr Tc Y Ru Zr Rh Nb Pd 6 Building Atoms - Period 5 Ag Sb Cd Te In I Sn Xe 7 Building Atoms - Period 6 Cs Ba La – 5d or 4f ? Elements for which the 4f-orbitals are being filled (La through Lu) are called lanthanides 8 Lanthanides – Period 6 Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 9 Chapter 6 Chemical Periodicity 10 Periodic Chart 1869 – Dmitri Mendeleev Established periodic trends in chemical and physical properties and predicted existence of unknown elements The properties of elements are periodic functions of their atomic weights (that’s an old statement of the periodic law) The properties of elements are periodic functions of their atomic numbers (that’s how we state it now) 11 Periodicity H 1s1 He Ne [He]2s22p6 Li [He]2s1 Ar [Ne]3s23p6 Na [Ne]3s1 Kr [Ar]3d104s24p6 K [Ar]4s1 Xe [Kr]4d105s25p6 Rb [Kr]5s1 Rn [Xe]4f145d106s26p6 Cs [Xe]6s1 1s2 12 Periodic Chart The periodicity in the properties of elements is caused by the periodicity in their electronic configurations Depending on the orbitals (subshells) being filled we distinguish: s-elements p-elements d-elements f-elements 13 Noble Gases & Alkali Metals He 1s2 Ne [He]2s22p6 Li [He]2s1 Ar [Ne]3s23p6 Na [Ne]3s1 Kr [Ar]3d104s24p6 K [Ar]4s1 Xe [Kr]4d105s25p6 Rb [Kr]5s1 Rn [Xe]4f145d106s26p6 Cs [Xe]6s1 14 Atomic Radii Describe the relative sizes of atoms How can we measure atomic radii? Atomic radii for all elements are tabulated based on the averaged data collected from many such measurements 15 Shielding effect Effective nuclear charge, Zeff, experienced by an electron is less than the actual nuclear charge, Z Electrons in the outermost shell are repelled (shielded) by electrons in the inner shells. This repulsion counteracts the attraction caused by the positive nuclear charge Coulomb’s Law: q1 r q2 q1 ⋅ q2 F ∝− 2 r 16 Atomic Radii: Periodicity q1 ⋅ q2 F ∝− 2 r As we move from left to right along the period, the effective nuclear charge “felt” by the outermost electron increases while the distance from the nucleus doesn’t change that much (electrons are filling the same shell) Outermost electrons are attracted stronger by the nucleus, and the atomic radius decreases 17 Atomic Radii: Periodicity As we move down the group, the principal quantum number increases and the outermost electrons appear farther away from the nucleus – the atomic radius increases 18 Example Arrange these elements based on their atomic radii Se, S, O, Te 19 Reading Assignment Go through Tuesday and Thursday lecture notes Read Chapter 5 and Section 4-1 of Chapter 4 Learn Key Terms from Chapter 5 (p. 221-222) 20 Important Dates Homework #2 due by 10/1 Monday (10/3) and Tuesday (10/4) – lecture quiz #2 based on Chapter 5 Homework #3 due by 10/10 (assignments can be found on the course web site) 21
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