CM4131 Principles of Inorganic Chemistry: Atomic Properties PDF

The Periodic Table s-block p-block d-block The elements are arranged based on repeating patterns in the electronic configuration of atoms. This results in recurring trends in properties of elements....

The Periodic Table s-block p-block d-block The elements are arranged based on repeating patterns in the electronic configuration of atoms. This results in recurring trends in properties of elements. f-block Inside the Atom ▪ In an atom with many electrons, each negatively charged electron is simultaneously attracted to the positively charged nucleus and repelled by other negatively charged electrons. negatively charged electrons repel negatively charged electrons positively charged nucleus attract negatively charged electrons Nuclear Charge ▪ The nuclear charge (Zactual) refers to the total positive charge located within the nucleus, which is equivalent to the number of protons. ▪ The higher the number of protons, the higher the nuclear charge, the stronger the attraction of an electron to the nucleus. element spdf notation Zactual 3Li 1s2 2s1 3 13Al 1s2 2s2 2p6 3s2 3p1 13 34Se 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4 34 Screening Effect ▪ The screening effect () refers to the reduction in nuclear charge due to the core electrons that “screen” outer electrons from the full effect of the nucleus. ▪ The higher the number of core electrons, the higher the screening effect, the weaker the attraction of an electron to the nucleus. element spdf notation Zactual  3Li 1s2 2s1 3 2 13Al 1s2 2s2 2p6 3s2 3p1 13 10 34Se 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4 34 28 Note: The screening effect of same shell electrons are ignored as they are less significant than the screening effect of core electrons. Effective Nuclear Charge ▪ The net effect of the nuclear charge and screening effect is known as the effective nuclear charge or net nuclear charge (Zeff). ▪ The higher the effective nuclear charge, the stronger the attraction of an electron to the nucleus. Zeff = Zactual –  element spdf notation Zactual  Zeff 3Li 1s2 2s1 3 2 1 13Al 1s2 2s2 2p6 3s2 3p1 13 10 3 34Se 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p4 34 28 6 Effective Nuclear Charge ▪ The net effect of the nuclear charge and screening effect is known as the effective nuclear charge or net nuclear charge (Zeff). ▪ The higher the effective nuclear charge, the stronger the attraction of an electron to the nucleus. Zeff = Zactual –  element spdf notation Zactual  Zeff 13Al 1s2 2s2 2p6 3s2 3p1 13 10 3 13Al 1s2 2s2 2p6 3s2 3p1 13 2 11 13Al 1s2 2s2 2p6 3s2 3p1 13 0 13 Study Check (Page 44) 1. Which will experience greater effective nuclear charge, the electrons in the n = 3 shell of Ar or the n = 3 shell of Kr? Which will be closer to the nucleus? element spdf notation Zactual  Zeff 18Ar 1s2 2s2 2p6 3s2 3p6 18 10 8 36Kr 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 36 10 26 The electrons in n = 3 of Kr will experience greater effective nuclear charge and hence stronger attraction to the nucleus. Thus, the electrons in n = 3 of Kr will also be closer to the nucleus. Effective Nuclear Charge (Across a Period) [Ne] 3s1 [Ne] 3s2 3p3 [Ne] 3s2 3p5 [Ne] 3s2 3p1 [Ne] 3s2 3p2 [Ne] 3s2 3p4 [Ne] 3s2 [Ne] 3s2 3p6 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar Zactual 11 12 13 14 15 16 17 18  10 10 10 10 10 10 10 10 Zeff 1 2 3 4 5 6 7 8 Zactual increases  ~ constant Zeff increases Effective Nuclear Charge (Across a Period) Across a Period: effective nuclear charge ▪ The nuclear charge increases as the number of protons increases. ▪ The screening effect remains relatively constant as the number of core electrons remain the same. ▪ Hence, the effective nuclear charge increases. Na Mg Al Si P S Cl Effective Nuclear Charge (Down a Group) [He] 2s2 Zactual  Zeff [Ne] 3s2 4Be 4 2 2 12Mg 12 10 2 [Ar] 4s2 20Ca 20 18 2 38Sr 38 36 2 [Kr] 5s2 56Ba 56 54 2 [Xe] 6s2 Zactual increases  increases Zeff ~constant Effective Nuclear Charge (Down a Group) Down a Group: effective nuclear charge ▪ The nuclear charge increases as the number of protons increases. ▪ The screening effect also increases as the number of core electrons increases. ▪ Hence, effective nuclear charge does not change significantly. Be Mg Ca Sr Ba  Effective Nuclear Charge (Across d-Block) [Ar] 3d1 4s2 [Ar] 3d3 4s2 [Ar] 3d5 4s2 [Ar] 3d7 4s2 [Ar] 3d10 4s1 [Ar] 3d2 4s2 [Ar] 3d5 4s1 [Ar] 3d6 4s2 [Ar] 3d8 4s2 [Ar] 3d10 4s2 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn Zactual 21 22 23 24 25 26 27 28 29 30  19 20 21 23 23 24 25 26 28 28 Zeff 2 2 2 1 2 2 2 2 1 2 Zactual increases  ~ increases Zeff no trend? Effective Nuclear Charge (Across d-Block) ▪ The nuclear charge increases as the effective nuclear charge number of protons increases. ▪ The screening effect also increases as the number of core electrons increases. ▪ The effective nuclear charge increases as increase in nuclear charge is only partially offset by the screening effect. ▪ This is due to the poor screening effect of the electrons in the d orbitals. Note: The increase in effective nuclear Sc Ti V Cr Mn Fe Co Ni Cu Zn charge is less than the increase across the main group elements. Atomic Radius ▪ Atomic radius is defined as the distance between the nucleus of an atom and its outermost (or valence) electron. ▪ The measurement is difficult because electrons are in constant random motion and do not reside in orbitals with “fixed” boundaries. ▪ Instead, atomic radius is estimated by measuring the distance between the nuclei of two adjacent atoms and then halving the distance. metallic radius covalent radius van der Waals’ radius Atomic Radius (Predictions?) effective nuclear charge effective nuclear charge Na Mg Al Si P S Cl Be Mg Ca Sr Ba Across a Period Down a Group Atomic Radius (Across a Period) Across a Period: atomic radius (nm) ▪ The nuclear charge increases as the 0.20 number of protons increases. 0.18 ▪ The screening effect remains relatively constant as the number of core 0.16 electrons remain the same. 0.14 ▪ Hence, the effective nuclear charge increases. 0.12 ▪ The attraction between nucleus and 0.10 outermost electrons increases. ▪ Thus, atomic radius decreases. 0.08 Na Mg Al Si P S Cl Atomic Radius (Down a Group) Down a Group: atomic radius (nm) ▪ The effective nuclear charge does not change significantly. 0.21 ▪ However, principal quantum number 0.19 for the outermost electrons increases. ▪ The outermost electrons are further 0.17 from the nucleus 0.15 ▪ Thus, atomic radius increases. 0.13 0.11 Be Mg Ca Sr Ba Atomic Radius (Across d-Block) Across the d Block: effective nuclear charge ▪ The nuclear charge increases as the number of protons increases. ▪ The screening effect also increases as the number of core electrons increases. ▪ The effective nuclear charge increases as increase in nuclear charge is only partially offset by the screening effect. ▪ This is due to the poor screening effect of the electrons in the d orbitals. Sc Ti V Cr Mn Fe Co Ni Cu Zn Atomic Radius (Across d-Block) Across the d Block: atomic radius (nm) ▪ The nuclear charge increases as the 0.22 number of protons increases. 0.20 ▪ The screening effect also increases as 0.18 the number of core electrons increases. 0.16 ▪ The effective nuclear charge increases 0.14 as increase in nuclear charge is only 0.12 partially offset by the screening effect. 0.10 ▪ The attraction between nucleus and outermost electrons increases slightly. 0.08 ▪ Thus, atomic radius decreases slightly. Sc Ti V Cr Mn Fe Co Ni Cu Zn Ionic Radius (Across a Period) anion isoelectronic series: 18 electrons ▪ Across a period, two isoelectronic ionic radius (nm) series as shown are formed. 0.22 P3— ▪ An isoelectronic series is a group of 0.20 S2— Cl— ions with same number of electrons. 0.18 ▪ The screening effect across an 0.16 0.14 isoelectronic series remains constant. 0.12 ▪ For period 3: 0.10 Na+ ▪ cations (10 e–): 1s2 2s2 2p6 0.08 Mg2+ ▪ anions (18 e–): 1s2 2s2 2p6 3s2 3p6 0.06 Al3+ Si4+ 0.04 0.02 cation Na isoelectronic Mg Al Si P S Cl series: 10 electrons Ionic Radius (Across a Period) anion isoelectronic series: 18 electrons Across Each Isoelectronic Series: ionic radius (nm) ▪ The nuclear charge increases as the 0.22 P3— number of protons increases. 0.20 S2— Cl— ▪ The screening effect remains constant 0.18 as the number of electrons remain the 0.16 0.14 same. 0.12 ▪ Hence, the effective nuclear charge 0.10 Na+ increases. 0.08 Mg2+ ▪ The attraction between nucleus and 0.06 Al3+ Si4+ outermost electrons increases. 0.04 ▪ Thus, ionic radius decreases. 0.02 cation Na isoelectronic Mg Al Si P S Cl series: 10 electrons Ionic Radius (Across a Period) Atomic vs Cationic Radius: ionic radius (nm) ▪ The nuclear charge is unchanged as 0.22 P3— number of protons remains the same. 0.20 S2— Cl— ▪ The screening effect decreases as the 0.18 number of electrons decreases. 0.16 0.14 ▪ Hence, the effective nuclear charge 0.12 increases. 0.10 Na+ ▪ The attraction between nucleus and 0.08 Mg2+ outermost electrons increases. 0.06 Al3+ Si4+ ▪ Thus, cationic radius is smaller than its 0.04 corresponding atom. 0.02 cation Na isoelectronic Mg Al Si P S Cl series: 10 electrons Ionic Radius (Across a Period) anion isoelectronic series: 18 electrons Atomic vs Anionic Radius: ionic radius (nm) ▪ The nuclear charge is unchanged as 0.22 P3— number of protons remains the same. 0.20 S2— Cl— ▪ The screening effect increases as the 0.18 number of electrons increases. 0.16 0.14 ▪ Hence, the effective nuclear charge 0.12 decreases. 0.10 Na+ ▪ The attraction between nucleus and 0.08 Mg2+ outermost electrons decreases. 0.06 Al3+ Si4+ ▪ Thus, anionic radius is larger than its 0.04 corresponding atom. 0.02 Na Mg Al Si P S Cl Ionic Radius (Across a Period) anion isoelectronic series: ionic radius (nm)18 electrons Cationic vs Anionic Radius: ▪ For period 3: 0.22 P3— ▪ cations (10 e–): 1s2 2s2 2p6 0.20 S2— Cl— ▪ anions (18 e–): 1s2 2s2 2p6 3s2 3p6 0.18 ▪ The principal quantum number for the 0.16 0.14 outermost electrons of the anions is 0.12 higher than that of the cations. 0.10 Na+ ▪ Thus, outermost electrons are further 0.08 Mg2+ from the nucleus and anionic radius is 0.06 Al3+ Si4+ larger than cationic radius. 0.04 0.02 cation Na isoelectronic Mg Al Si P S Cl series: 10 electrons Ionic Radius (Down a Group) Down a Group: ionic radius (nm) ▪ The nuclear charge increases as the 0.20 number of protons increases. ▪ The screening effect also increases as 0.15 Ba2+ the number of core electrons Sr2+ increases. Ca2+ ▪ Hence, effective nuclear charge does 0.10 Mg2+ not change significantly. ▪ However, principal quantum number 0.05 Be2+ for the outermost electrons increases. ▪ Thus, outermost electrons are further 0.00 from the nucleus and ionic radius Be Mg Ca Sr Ba increases. Study Check (Page 48) 1. For each of the following sets of atoms and ions, arrange the species in order of increasing size. (a) Se2—, Te2—, Se element spdf notation Zactual  Zeff 34Se [Ar] 3d10 4s2 4p4 34 28 6 34Se2— [Ar] 3d10 4s2 4p6 34 28 slightly