Section 4

What’s significant about all valence orbitals of noble gases being filled?

• maximized spin exchange stabilization energy (energy gained when e^- with opposite spins are paired within same orbital)

• due to stable e^- configuration, noble gases are inert + don’t readily react with other elements

Many properties of elements depend upon?

Their valence shell e^- configuraiton.

What is the 1st ionization energy?

• energy required to remove the outer e^- (highest energy) from an atom in the gas phase

• X(g) + energy(light) ➡ X⁺(g) + e^-

• ∆E = E_products - E_reactants

  • energy provided to reactants to eject an e^-

What do ionization energies give direct measurements of?

Valence e^- energies.

What are the 3 trends of ionization energy?

1. across a row (L to R): 1st IE increases

   1. net (+) charge experienced by valence e^- is due to Z_eff increasing (more protons)

   2. screening by e^- in same shell less than core e^-

      1. valence e^- don’t shield each other as effectively as core e^- do, so increasing the (+) charge of nucleus more strongly is felt by the valence e^-, making them being held more tightly

2. down a group: 1st IE decreases

   1. principle QN increases ➡ E of orbital increases (e^- in higher orbitals easier to remove than in lower orbitals)

      1. # core e^- increases down the group ➡ more screening + less Z_eff

3. ionization potential drops s² ➡ s²p + s²p³ ➡ s²p⁴

   1. s² ➡ s²p

      1. adding 1st p-e^- leads to drop in IE since p-orbitals are higher in energy + easier to remove than s-orbitals

   2. s²p³ ➡ s²p⁴

      1. p-orbitals are half-filled in s²p³ (stable due to symmetrical distribution + minimized e^- repulsion)

      2. but adding a 4th e^- in s²p⁴ forces pairing within a p-orbital, increasing e^- repulsion + lowering IE

What is atomic radii + 3 types of it?

• distance from nucleus of an atom to the outermost e^- shell: size

• types

  • single bond (covalent): measure distance between nucleii (single bond) + divide by 2

  • van der Waals: outer e^- in one atom is weakly attracted to another atom’s nucleus

    • ½ distance between nucleii

  • ionic radii: ionic solids after gaining or losing e^- compared to neutral atom

    • measure distance between nucleii + extrapolate to neutral atomic radii

What are the 2 trends of atomic radii?

1. atomic radius increases down a group

   1. principle QN increases ➡ energy of orbital increases + # core e^- increases

   2. more shells are being added

2. atomic radius generally decreases across a row (L to R)

   1. # protons + # core e^- increase left to right

      1. Z_eff increases left to right (more protons)

      2. atom size decreases since e^- are being pulled in more

What is the order of shielding ability for s, p, d + f-orbitals?

• s > p > d > f

  • e^- in f-orbitals are less effective at screening nuclear charge than e^- in s + p-orbitals

  • d-orbitals: requires 10 e^- to fill orbitals + 10 protons in nucleus

    • ex. between Ca + Ga the 3d orbitals are filled, but d-e^- don’t shield nuclear charge effectively

      • thus Ga has a smaller atomic radius than Al even though Al is above it in period table (d-orbital contraction)

What is electronegativity?

Atom’s relative ability to attract e^- in interactions with other atoms, solids, metals, molecules, covalent/ionic bonding.

What are the 2 trends for electronegativity?

1. EN increases L to R (along with Z_eff)

2. EN decreases down a group (due to screening)