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ibchem/IB/ibfiles/ periodicity /per_ppt/pt_trends

5 Periodic Trends (aka Periodicity): 1) Atomic Radius 2) Ionic Radius 3) Ionization Energy 4) Electron Affinity 5) ElectroNegativity. ibchem.com/IB/ibfiles/ periodicity /per_ppt/pt_trends.ppt. Periodic Law.

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ibchem/IB/ibfiles/ periodicity /per_ppt/pt_trends

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  1. 5 Periodic Trends(aka Periodicity):1) Atomic Radius2) Ionic Radius3) Ionization Energy4) Electron Affinity5) ElectroNegativity ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  2. Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties. local.ans.org/mi/Teacher_CD/.../Hist_PeriodicTable.ppt

  3. Trends in Atomic Size • First problem: Where do you start measuring from? • The electron cloud doesn’t have a definite edge. • They get around this by measuring more than 1 atom at a time. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  4. Atomic Size } • Atomic Radius = half the distance between two nuclei of a diatomic molecule. Radius ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  5. Trends in Atomic Size • Influenced by three factors: 1. Energy Level • Higher energy level is further away. 2. Charge on nucleus • More charge pulls electrons in closer. • 3. Shielding effect e <-> e repulsion ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  6. Group trends H • As we go down a group... • each atom has another energy level, • so the atoms get bigger. Li Na K Rb ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  7. Periodic Trends • As you go across a period, the radius gets smaller. • Electrons are in same energy level. • More nuclear charge. • Outermost electrons are closer. Na Mg Al Si P S Cl Ar ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  8. Atomic Radii Figure 8.9 xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

  9. Effective Nuclear Charge, Z* • Z* is the nuclear charge experienced by the outermost electrons. • Z* increases across a period owing to incomplete shielding by inner electrons. • Estimate Z* by --> [ Z - (no. inner electrons) ] • Z=Atomic Number • Charge felt by e- in Li:Z* = Z-#Inner e-=3 - 2 = 1 • Be Z* = 4 - 2 = 2 • B Z* = 5 - 2 = 3 and so on! xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

  10. Shielding • The electron in the outermost energy level experiences more inter-electron repulsion (shielding). • Second electron has same shielding, if it is in the same period ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  11. + + Li , 78 pm 2e and 3 p Ion Sizes Forming a cation. • CATIONS are SMALLER than the atoms from which they come. • The electron/proton attraction has gone UP and so size DECREASES. Li,152 pm 3e and 3p xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

  12. - - F, 71 pm F , 133 pm 9e and 9p 10 e and 9 p Ion Sizes 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. xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

  13. Trends in Ionic Size • Cations form by losing electrons. • Cations are smaller that the atom they come from. • Metals form cations. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  14. Ionic size • Anions form by gaining electrons. • Anions are bigger that the atom they come from. • Nonmetals form anions. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  15. Group trends Li1+ • Adding energy level • Ions get bigger as you go down. Na1+ K1+ Rb1+ Cs1+ ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  16. Periodic Trends • Across the period, nuclear charge increases so they get smaller. • Energy level changes between anions and cations. N3- O2- F1- B3+ Li1+ C4+ Be2+ ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  17. Trends in Ion Sizes Figure 8.13 xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

  18. Trends in Ionization Energy • The amount of energy required to completely remove an electron from a gaseous atom. • Removing an electron makes a +1 ion. • The energy required to remove the first electron is called the first ionization energy. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  19. Ionization Energy • The second ionization energy is the energy required to remove the second electron(s). • Always greater than first IE. • The third IE is the energy required to remove a third electron, which is greater than 1st or 2nd IE. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  20. Symbol First Second Third 5247 7297 1757 2430 2352 2857 3391 3375 3963 1312 2731 520 900 800 1086 1402 1314 1681 2080 HHeLiBeBCNO F Ne 11810 14840 3569 4619 4577 5301 6045 6276 ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  21. Symbol First Second Third 11810 14840 3569 4619 4577 5301 6045 6276 5247 7297 1757 2430 2352 2857 3391 3375 3963 1312 2731 520 900 800 1086 1402 1314 1681 2080 HHeLiBeBCNO F Ne ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  22. Ionization EnergySee Screen 8.12 IE = energy required to remove an electron from an atom in the gas phase. Mg (g) + 738 kJ ---> Mg+ (g) + e- xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

  23. Ionization EnergySee Screen 8.12 Mg (g) + 735 kJ ---> Mg+ (g) + e- Mg+ (g) + 1451 kJ ---> Mg2+ (g) + e- Mg2+ (g) + 7733 kJ ---> Mg3+ (g) + e- Energy cost is very high to dip into a lower shell. xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

  24. What determines IE • The greater the nuclear charge, the greater IE. • Greater distance from nucleus decreases IE • Shielding effect ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  25. Group trends • As you go down a group, first IE decreases because... • The electron is further away. • More shielding. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  26. Periodic trends • All the atoms in the same period have the same energy level. • Same shielding. • But, increasing nuclear charge • So IE generally increases from left to right. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  27. Trends in Electron Affinity • The energy change associated with adding an electron to a gaseous atom(s). • Easiest to add to group 7A or 17(Halogens). • Gets them to full energy level. • Increase from left to right: atoms become smaller, with greater nuclear charge. • Decrease as we go down a group. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  28. Electron Affinity A few elements GAIN electrons to form anions. Electron affinity is the energy change when an electron is added: A(g) + e- ---> A-(g) E.A. = ∆E xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

  29. 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 xbeams.chem.yale.edu/~batista/113/chapter8/ch8.ppt

  30. Electronegativity • The tendency for an atom to attract electrons to itself when it is chemically combined with another element. • High electronegativity means it pulls the electron toward it. • Atoms with large negative electron affinity have larger electronegativity. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  31. Group Trend • The further down a group, the farther the electron is away, and the more electrons an atom has. • More willing to share. • Low electronegativity. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  32. Periodic Trend • Metals are at the left of the table. • They let their electrons go easily • Low electronegativity • At the right end are the nonmetals. • They want more electrons. • Try to take them away from others • High electronegativity. ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  33. Ionization energy and ElectroNegativity INCREASE ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

  34. Atomic size INCREASES, shielding constant Ionic size increases ibchem.com/IB/ibfiles/periodicity/per_ppt/pt_trends.ppt

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