Ch2c Flashcards
How are exceptions to the trends of effective nuclear charge explained?
They are explained by changes in e- configuration (Egap, pairing & exchange energy).
What are four atomic parameters?
1) IE
2) EA
3) Electronegativity
3) atomic radii.
Define ionization energy.
It is the energy required to remove an e- from the highest occupied orbital of the ground state.
Is ionization an endothermic or exothermic process?
Endothermic process because energy is being put in rather than released.
How does effective nuclear charge explain the “stability” of noble gases?
When comparing the effective nuclear charge experienced by the outer most e-, e- of Li+ is held much more tightly by the nucleus than the first e- removed.
What is the general trend for ionization energy in the periodic table?
decreases down a group since e- lost comes from larger sub shell, and increases across a period due to shielding by other e-s.
Describe the IE’s of TMs.
They remain roughly constant.
Define Electron Affinity (EA).
It is the energy required to remove an electron from an anion, and the e- is assumed to come from the lowest occupied orbital of the ground state anion.
What is another term for electron affinity?
zeroth IE of the neutral atom.
Is electron affinity an endothermic or exothermic process?
It can be either.
What is the general trend for electron affinity in periodic table?
There is less energy needed to remove e- from an anion because of the additive shielding.
Increases across a period due to higher effective nuclear charge.
Do we look at the neutral atom or anion when assessing EA?
Anion.
Which group of element has the lowest EA and is the process exo/or endothermic?
Noble gases, exothermic.
Why do noble gases have negative EA’s?
It is an exothermic process (energy is being released), because the e- being removed comes from a higher energy level, so the regular noble has configuration e-s intensely shield this extra electron in its larger orbital.
What does LUMO and HOMO stand for?
LUMO: Lowest Unoccupied Molecular Orbital.
HOMO: Highest Occupied Molecular Orbital.
Define electronegativity.
Electronegativity is a measure of the tendency for one element of a bonded pair to attract the e-s associated with the bond itself.
What scale is used to estimate electronegativity of an element?
The Pauling Scale.
How is polarity of a bond measured?
The polarity of a bond is measured by comparing the electronegativities of the two bonded elements.
What does electronegativity discuss?
The properties and reactivities of molecules.
Name four proposed scales of electronegativity.
- Mulliken.
- Allen.
- Allred and Rochow.
- Pauling, most commonly used.
Define the Mulliken scale of electronegativity.
An atom will have a high electronegativity if it has a high ionization energy, or positive electron affinity.
How did Mulliken calculate electronegativity?
He used the average of ionization energy and electron affinity. (short: average of IE & EA)
Define the Allen scale of electronegativity.
Designed for main group elements, in which used configuration energy or average of ionization enthalpy data for s & p valence electron. (short: average E of valence shell e-s)
Define the Allred and Rochow scale of electronegativity.
Bonding e- is held by the effective nuclear charge it experiences, thus has a force resisting its removal. He assumed the electronegativity was proportional to this resisting force. (short: electrostatic attraction to nucleus, is proportional to Z*/r2)
