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Periodic Relationships Among the Elements

Periodic Relationships Among the Elements. Chapter 8. Higher effective nuclear charge. Electrons held more tightly. Larger orbitals. Electrons held less. tightly. Shielding Effect!. General Periodic Trends. Atomic and ionic size Ionization energy Electronegativity Electron Affinity.

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Periodic Relationships Among the Elements

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  1. Periodic Relationships Among the Elements Chapter 8

  2. Higher effective nuclear charge Electrons held more tightly Larger orbitals. Electrons held less tightly. Shielding Effect! General Periodic Trends • Atomic and ionic size • Ionization energy • Electronegativity • Electron Affinity

  3. Core Radius Z Zeff Na 11 10 1 186 Mg 12 10 2 160 Al 13 10 3 143 Si 14 10 4 132 Effective nuclear charge (Zeff) is the “positive charge” felt by an electron. Zeff Z – number of inner or core electrons 8.3

  4. Effective Nuclear Charge (Zeff) increasing Zeff increasing Zeff 8.3

  5. 8.3

  6. 8.3

  7. Atomic Radii 8.3

  8. Atomic Size • Size goes UP on going down a group. • Because electrons are added further from the nucleus, there is less attraction. This is due to additional energy levels and the shielding effect. Each additional energy level “shields” the electrons from being pulled in toward the nucleus.

  9. Atomic Size Size decreases across a period owing to increase in the effective nuclear charge. Small Large

  10. Cation is always smaller than atom from which it is formed. Anion is always larger than atom from which it is formed. 8.3

  11. 8.3

  12. 8.3

  13. I1 + X (g) X+(g) + e- I2 + X+(g) X2+(g) + e- I3 + X2+(g) X3+(g) + e- Ionization energy is the minimum energy (kJ/mol) required to remove an electron from a gaseous atom in its ground state. I1 first ionization energy I2 second ionization energy I3 third ionization energy I1 < I2 < I3 8.4

  14. 8.4

  15. Filled n=1 shell Filled n=2 shell Filled n=3 shell Filled n=4 shell Filled n=5 shell 8.4

  16. Increasing First Ionization Energy Increasing First Ionization Energy General Trend in First Ionization Energies 8.4

  17. X (g) + e- X-(g) F (g) + e- F-(g) O (g) + e- O-(g) Electron affinity is the negative of the energy change that occurs when an electron is accepted by an atom in the gaseous state to form an anion. DH = -328 kJ/mol EA = +328 kJ/mol DH = -141 kJ/mol EA = +141 kJ/mol 8.5

  18. 8.5

  19. 8.5

  20. M M+1 + 1e- 2M(s) + 2H2O(l) 2MOH(aq) + H2(g) 4M(s) + O2(g) 2M2O(s) Increasing reactivity Group 1A Elements (ns1, n  2) 8.6

  21. X + 1e- X-1 X2(g) + H2(g) 2HX(g) Increasing reactivity Group 7A Elements (ns2np5, n  2) 8.6

  22. Completely filled ns and np subshells. Highest ionization energy of all elements. No tendency to accept extra electrons. Group 8A Elements (ns2np6, n  2) 8.6

  23. acidic basic Properties of Oxides Across a Period Less acidic More acidic Less basic More basic 8.6

  24. Electronegativity,   is a measure of the ability of an atom in a molecule to attract electrons to itself. Concept proposed by Linus Pauling 1901-1994

  25. Periodic Trends: Electronegativity • In a group: Atoms with fewer energy levels can attract electrons better (less shielding). So, electronegativity increases UP a group of elements. • In a period: More protons, while the energy levels are the same, means atoms can better attract electrons. So, electronegativity increases RIGHT in a period of elements.

  26. Electronegativity

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