LEC 32 (7.4-7.5)

Quick Recap – Periodic Table

  • The periodic table exhibits periodicity due to the arrangement of valence electrons.

  • Effective Nuclear Charge: Increases as you move right and down the periodic table.

  • Bonding Radius: Increases as you move left and down the periodic table.

Practice Problem

  • Question: Which of the following has the largest radius? Cl-, K+, Na+, F-.

    • The radius increases down and to the left, but adding electrons to Cl- increases its radius more than losing electrons from K+.

Key Concepts for Today

  • Ionization Energy: Energy required to remove an electron from a gas atom or ion.

  • Electron Affinity: Likelihood of gaining an electron.

Ionization Energy

  • An ion forms when an atom loses or gains an electron, thus acquiring a charge.

  • Ionization Energy (IE): Minimum energy required to remove an electron from an atom.

Multiple Ionization Energies

  • First Ionization Energy (I1): Energy needed to remove the first electron.

  • Second Ionization Energy (I2), etc.: Energy to remove subsequent electrons.

    • Energy increases as you remove more electrons due to increased positive charge attracting remaining electrons more strongly.

Cracking Core Electron Shells

  • As moving from valence electrons to core electrons, the ionization energy skyrockets:

    • For example, for Sodium (Na): 1st IE = 496 kJ/mol, 2nd IE = 4562 kJ/mol.

Key Rules of Ionization Energy

  • Trends:

    • Increases left to right across a period.

    • Decreases top to bottom within a group.

    • S and P orbitals generally have higher energies than F and D orbitals.

Orbital Electron Loss

  • Electrons are removed from the orbital with the highest quantum number (n) first, regardless of energy.

  • For orbitals with the same n, electrons are lost from the orbital with the highest angular momentum quantum number (l).

Electron Affinity vs. Ionization Energy

  • Ionization Energy: Likelihood of losing electrons.

  • Electron Affinity: Likelihood of gaining electrons.

  • Trends in Electron Affinity:

    • Electron affinity varies based on the stability of new orbitals.

    • Single elements may exhibit exceptions in trends due to orbital filling dynamics (e.g., noble gases have low electron affinity).

Practice Problems

  1. Does energy increase from I1 to I2 to I3?

    • Answer: Yes, energy increases due to the atom becoming increasingly positively charged.

  2. Which orbital has higher ionization energy: 3s or 4p?

    • Answer: 3s has a higher ionization energy due to being closer to the nucleus.

  3. Which atom has the highest I2 energy?

    • Answer: Higher I2 is usually from an atom with core electron removal.

Trends in Electron Affinity

  • The balance between gaining stability and reluctance in filling new orbitals leads to imperfect trends.

  • For example, noble gases often have electron affinities near zero, while halogens have strong negative affinities due to their high electronegativity.