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1 PERIODIC TRENDS 2 Electron Filling Order Figure 8.5 3 Electron Configurations and the Periodic Table Figure 8.7 4 Phosphorus Group 5A Atomic number = 15 1s2 2s2 2p6 3s2 3p3 [Ne] 3s2 3p3 All Group 5A elements have [core ] ns2 np3 configurations where n is the period number. 3p 3s 2p 2s 1s Lithium 3p 3s 2p 2s 1s Group 1A Atomic number = 3 1s22s1 ---> 3 total electrons 5 Electron Properties Diamagnetic: NOT attracted to a magnetic field Paramagnetic: substance is attracted to a magnetic field. Substance has unpaired electrons. 6 7 Neon 3p 3s 2p 2s 1s Group 8A Atomic number = 10 1s2 2s2 2p6 ---> Diamagnetic 8 Beryllium 3p 3s 2p 2s 1s Group 2A Atomic number = 4 1s22s2 Diamagnetic Boron 3p 3s 2p 2s 1s 9 Group 3A Atomic number = 5 1s2 2s2 2p1 Paramagnetic Carbon 3p Group 4A Atomic number = 6 1s2 2s2 2p2 3s 2p 2s 1s Paramagnetic 10 11 Fluorine 3p 3s 2p 2s 1s Group 7A Atomic number = 9 1s2 2s2 2p5 ---> Paramagnetic Ion Configurations How do we know the configurations of ions? Determine the magnetic properties of ions. Ions with UNPAIRED ELECTRONS are PARAMAGNETIC. Without unpaired electrons DIAMAGNETIC. 12 13 transition metal ions Fe [Ar] 4s2 3d6 loses 2 electrons ---> Fe2+ [Ar] 4s0 3d6 Fe2+ Fe 4s 3d 4s 3d • loses 3 electrons ---> Fe3+ [Ar] 4s0 3d5 Fe2+ Fe 4s 3d 4s 3d Transition Metals How do they fill? How can we determine? Chromium Iron Copper 14 15 Ion Configurations Mn Mn [Ar] 4s2 3d5 ---> Mn5+ [Ar] 4s03d2 loses 5 electrons ---> Mn5+ [Ar] 4s2 3d0 2+ P Fe D Fe 4s 3d 4s 3d 16 PERIODIC TRENDS PERIODICITY Period Law-physical and chemical properties of elements are a periodic function of their atomic numbers 17 General Periodic Trends • Atomic and ionic size • Ionization energy • Electron affinity, electronegativity 18 Effective Nuclear Charge Z* 19 Effective Nuclear Charge, Z* • Z* is the nuclear charge experienced by the outermost electrons. See p. 295 and Screen 8.6. • Explains why E(2s) < E(2p) • Z* increases across a period owing to incomplete shielding by inner electrons. • Estimate Z* by --> [ Z - (no. inner electrons) ] • Charge felt by 2s e- in Li Z* = 3 - 2 = 1 • Be Z* = 4 - 2 = 2 • B Z* = 5 - 2 = 3 and so on! 20 Effective Nuclear Charge, Z* • Atom • • • • • • • Li Be B C N O F Z* Experienced by Electrons in Valence Orbitals +1.28 ------+2.58 Increase in +3.22 Z* across a +3.85 period +4.49 +5.13 21 General Periodic Trends Higher effective nuclear charge Electrons held more tightly Larger orbitals. Electrons held less tightly. 22 23 Lithium Periodic Trend in the Reactivity of Metals Sodium Potassium MOST 2. As Reactivity for Metals you go down a group for metals the number of energy levels increase. Because of this, reactivity increases because the atom is more willing to give away its electron (react). 3.Nonmetalic Trends: Gain electrons Nonmetals on right side, form anions Going right elements are more nonmetallic (better gainers of electrons) Going UP elements become more nonmetallic (want to gain) 8. Reactivity nonmetals: Gain e The reason Across = fill the energy level Going UP a group, nonmetals have same valence but fewer total electrons Flourine is the most reactive nonmetal. Atomic Radii 27 Figure 8.9 28 Atomic Size • Size increases, down a group. • Because electrons are added into additional energy levels, there is less attraction. • Size decreases across a period. • Because, increased effective nuclear charge. 29 Atomic Size Size decreases across a period owing to increase in Z*. Each added electron feels a greater and greater + charge. Large Small 30 Trends in Atomic Size See Figures 8.9 & 8.10 Radius (pm) 250 K 1st transition series 3rd period 200 Na 2nd period Li 150 Kr 100 Ar Ne 50 He 0 0 5 10 15 20 25 Atomic Number 30 35 40 31 Ion Sizes + Li,152 pm 3e and 3p Li + , 78 pm 2e and 3 p Forming a cation. • CATIONS are SMALLER than the atoms from which they come. • The electron/proton attraction has gone UP and so size DECREASES. 32 Ion Sizes F, 71 pm 9e and 9p F- , 133 pm 10 e and 9 p Forming an anion. • ANIONS are LARGER than the atoms from which they come. • The electron/proton attraction has gone DOWN and so size INCREASES. • Trends in ion sizes are the same as atom sizes. Trends in Ion Sizes Figure 8.13 33 Ionization Energy IE = energy required to remove an electron from an atom in the gas phase. Mg (g) + 738 kJ ---> Mg+ (g) + e- 34 Ionization Energy IE = energy required to remove an electron from an atom in the gas phase. Mg (g) + 738 kJ ---> Mg+ (g) + e- Mg+ (g) + 1451 kJ ---> Mg2+ (g) + eMg+ has 12 protons and only 11 electrons. Therefore, IE for Mg+ > Mg. 35 Ionization Energy 1st IE: Mg (g) + 735 kJ ---> Mg+ (g) + e2nd IE: Mg+ (g) + 1451 kJ ---> Mg2+ (g) + e- 3rd IE: Mg2+ (g) + 7733 kJ ---> Mg3+ (g) + eEnergy cost is very high to dip into a shell of lower n (core electrons). This is why ox. no. = Group no. 36 37 Trends in Ionization Energy 1st Ionization energy (kJ/mol) 2500 He Ne 2000 Ar 1500 Kr 1000 500 0 1 H 3 Li 5 7 9 11 Na 13 15 17 19 K 21 23 25 27 29 31 Atomic Number 33 35 38 Trends in Ionization Energy • IE decreases down a group • Because size increases. • IE increases across a period • Because effective nuclear charge increases 39 Electron Affinity A few elements GAIN electrons to form anions. Electron affinity is the energy involved when an atom gains an electron to form an anion. X(g) + e- ---> X-(g) E.A. = ∆E Trends in Electron Affinity 40 41 Trends in Electron Affinity • Affinity for electron increases across a period (EA becomes more negative). • Affinity decreases down a group (EA becomes less negative). Atom EA F -328 kJ Cl -349 kJ Br -325 kJ I -295 kJ 42 Electron Affinity of Oxygen O atom [He] + electron O- ion [He] EA = - 141 kJ ∆E is EXOthermic because O has an affinity for an e-. 43 Electron Affinity of Nitrogen N atom [He] + electron N- ion [He] EA = 0 kJ ∆E is zero for Ndue to electronelectron repulsions. 44 Electronegativity • So how is this different from electron affinity? • Electron Affinity – is rating of how well an atom wants to gain an electron • Electronegativity – is rating of how well an atom keeps the electron once it is bonded to another atom 45 Electronegativity Electron Configurations and the Periodic Trends 46 47 “Your Best Friend” • Periodic table