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Catalyst

Catalyst. 1. 2. 3 . What are the trends for atomic radii? Why do these trends exist ? 4. Down in Front!. Today’s Learning Targets. 1.9 – I can define and calculate the effective nuclear charge for an atom and explain how this impacts observed periodic trends .

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Catalyst

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  1. Catalyst 1. 2. 3. What are the trends for atomic radii? Why do these trends exist? 4.

  2. Down in Front!

  3. Today’s Learning Targets • 1.9 – I can define and calculate the effective nuclear charge for an atom and explain how this impacts observed periodic trends. • 1.10 – I can define atomic/ionic radius and explain how it relates to the effective nuclear charge. Furthermore, I can explain how this trend changes as you move throughout the Periodic Table and relate it to the elements quantum electron configuration.

  4. Coulomb’s Law • The force felt by two charged objects is directly related to the size of the charge and inversely related to the distance between the charges. • The force on the electron increases as the nuclear charge increases • The force on the electron decreases as the nuclear charge decreases

  5. Effective Nuclear Charge • Periodic trends depend on how well electrons “feel” the nucleus • The effective nuclear charge (Zef) is the force felt between the nucleus and the electron of interest

  6. Electron Shielding • In elements with many electrons, inner electrons shield the valence electrons. • This occurs because the core electrons act to shield the valence electrons from the full positive charge of the nucleus.

  7. Predict the Trend • Do you think the Zef increases or decreases as we go down a group the Periodic Table? • What about as we go across a period? • Justify your answer with evidence and the idea of electron shielding.

  8. Trends in Zef • The further away from the nucleus, the less the nuclear charge is “felt”,so Zef decreases down a group. • As you continue across a period, there are no more core electrons, but there is a stronger positive charge • Therefore, as you go across a period Zef increases.

  9. Zef increases Zef decreases

  10. Quick Write • What is the trend for atomic radii as you go throughout the Periodic Table? Justify your response

  11. Trends for Atomic Radii • Atomic radii increase down a group and decrease across a period. • They increase down a group because more orbitals are being added, making the element “bulkier” • The decrease across a period because Zef is increasing, thus causing the electron to be more attracted to the nucleus.

  12. Radii of Cations • Removing electrons causes the radius to decrease • Removing electrons causes orbitals to be removed and electron-electron repulsions to decrease • Both of these lead to an increase in Zef and a decrease in the ionic radius

  13. Radii of Anions • Adding electrons causes the radius to increase • Adding electrons causes an increase in electron – electron repulsions, so Zef decreases. • A decrease is Zef causes the radius to be larger

  14. Class Example • Arrange Na+, K+, and K in order of increasing atomic radius

  15. Table Talk • Arrange the ions K+, Cl-, Ca2+, and S2- in order of decreasing size.

  16. Table Talk • Arrange the following atoms from smallest to largest: Rb+, Sr2+, Y3+

  17. Summarize

  18. Pick a Side • I am going to project up numerous statements • You must decide whether you agree or disagree. • Be prepared to defend your response!

  19. Pick a Side Questions • Coulombs Law says that as you pull charges away from one another, the force increases. • The effective nuclear describes the attraction between the nucleus and the electron of interest. • Effective nuclear charge decreases down a group because there are more electrons. • Effective nuclear charge increases across a period because of the more positive nucleus. • The ionic radius is always larger than the atomic radius for a given atom.

  20. Pick a Side Questions (cont.) 5. Order the following from smallest to largest radius: Se2-, Te2-, Se - Answer: Se, Se2-, Te2 6. Order the following from largest to smallest radius: Co3+, Fe2+, Fe3+ - Answer: Co3+, Fe2+, Fe3+ 7. The effective nuclear charge has littler overall impact on the atomic and ionic radius of an element

  21. Closing Time • Pre – Lab for Lab 3 due at the start of lab on Thursday/Friday • Final lab right up (results and conclusions) due Monday/Tuesday for Lab 2. • To be on track, read sections 7.1 – 7.3 and answer the corresponding problems

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