Ch2c

Question 1

How are exceptions to the trends of effective nuclear charge explained?

Answer 1

They are explained by changes in e- configuration (Egap, pairing & exchange energy).

Question 2

What are four atomic parameters?

Answer 2

1) IE
2) EA
3) Electronegativity
3) atomic radii.

Question 3

Define ionization energy.

Answer 3

It is the energy required to remove an e- from the highest occupied orbital of the ground state.

Question 4

Is ionization an endothermic or exothermic process?

Answer 4

Endothermic process because energy is being put in rather than released.

Question 5

How does effective nuclear charge explain the “stability” of noble gases?

Answer 5

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.

Question 6

What is the general trend for ionization energy in the periodic table?

Answer 6

decreases down a group since e- lost comes from larger sub shell, and increases across a period due to shielding by other e-s.

Question 7

Describe the IE’s of TMs.

Answer 7

They remain roughly constant.

Question 8

Define Electron Affinity (EA).

Answer 8

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.

Question 9

What is another term for electron affinity?

Answer 9

zeroth IE of the neutral atom.

Question 10

Is electron affinity an endothermic or exothermic process?

Answer 10

It can be either.

Question 11

What is the general trend for electron affinity in periodic table?

Answer 11

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.

Question 12

Do we look at the neutral atom or anion when assessing EA?

Answer 12

Anion.

Question 13

Which group of element has the lowest EA and is the process exo/or endothermic?

Answer 13

Noble gases, exothermic.

Question 14

Why do noble gases have negative EA’s?

Answer 14

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.

Question 15

What does LUMO and HOMO stand for?

Answer 15

LUMO: Lowest Unoccupied Molecular Orbital.
HOMO: Highest Occupied Molecular Orbital.

Question 16

Define electronegativity.

Answer 16

Electronegativity is a measure of the tendency for one element of a bonded pair to attract the e-s associated with the bond itself.

Question 17

What scale is used to estimate electronegativity of an element?

Answer 17

The Pauling Scale.

Question 18

How is polarity of a bond measured?

Answer 18

The polarity of a bond is measured by comparing the electronegativities of the two bonded elements.

Question 19

What does electronegativity discuss?

Answer 19

The properties and reactivities of molecules.

Question 20

Name four proposed scales of electronegativity.

Answer 20

1. Mulliken.
2. Allen.
3. Allred and Rochow.
4. Pauling, most commonly used.

Question 21

Define the Mulliken scale of electronegativity.

Answer 21

An atom will have a high electronegativity if it has a high ionization energy, or positive electron affinity.

Question 22

How did Mulliken calculate electronegativity?

Answer 22

He used the average of ionization energy and electron affinity. (short: average of IE & EA)

Question 23

Define the Allen scale of electronegativity.

Answer 23

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)

Question 24

Define the Allred and Rochow scale of electronegativity.

Answer 24

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)

Question 25

Define the Pauling Scale of electronegativity.

Answer 25

It is not directly based on IE or EA, instead considers the difference in bond strength between a bonds real strength and calculated strength with the use of dissociation energies of (perfectly covalent bonds). Partially ionic bonds would have a HIGHER observed dissociation energy, therefore the difference will be proportional to the difference in electronegativities.

Question 26

The bond energies of H-H & F-F are 436 & 158 kJ/mol. If the H-F were perfectly covalent (it is not) the bond energy would be predicted to be (436x158)^(1/2) =262. What is actually observed?

Answer 26

Experimental H-F bond is 566 kJ/mol, so the difference (566-262=304) 304 kJ/mol is proportional to the difference in electronegativities.

Question 27

What is the Pauling Scale formula for electronegativity?

Answer 27

difference electronegativities= 0.102sqrt(difference in dissociation energy of perfectly covalent bonds)

Question 28

General trend for electronegativity in the periodic table.

Answer 28

Increases across a period and decreases down a group.

Question 29

Define metallic radius.

Answer 29

Half the distance between the nuclei of metal atoms in the solid state.

Question 30

Define covalent radius.

Answer 30

Half of the internuclear distance between the nuclei of two single-bonded atoms of the same species (homonuclear) The values are given for different bond orders (single, double, triple).

Question 31

What is the collective term of metallic and covalent radius?

Answer 31

Atomic radius.

Question 32

Define atomic radius.

Answer 32

Half the diameter of a neutral atom.

Question 33

Define Van des Waal’s radius.

Answer 33

Half the distance between two unbonded atoms. Limits the closest approach of two non-bonded atoms.

Question 34

General trend for single bond of non-polar covalent radii in periodic table.

Answer 34

increases down a group as new shells are used, and decreases across a row due to partial shielding by electrons in the same shel (recall: partila just means as Z* increases by one sigma increase by 0.35).

Question 35

Where are lanthanides inserted in the periodic table?

Answer 35

Into the 6th row d-block.

Question 36

What is the “Lanthanide Contraction”?

Answer 36

The insertion of the Lanthanides results in transition metals smaller than expected and roughly the same size as 5th row transition metals. Thus the covalent radius trend is not observed due to the effect of 14 lanthanides. As a consequence 2nd and 3rd row of TMs are more similar in covalent radii than the 1st row of TMs.

Question 37

Define ionic radius.

Answer 37

The radius of an atom’s ion in ionic crystals structure.

Question 38

Ionic radius of anion vs. cation.

Answer 38

The bigger the positive charge on the cation the smaller the ionic radius, because the atom will begin to lose e- shells. The bigger the negative charge the bigger the ionic radius, because e-s are added to shells and nuclear effective charge decreases.

Question 39

How are ion sizes explained by effective nuclear charge?

Answer 39

• Cations are smaller than parent atoms, because fewer e-s will decrease the shielding, thus e-s will be held more tightly by the nucleus. The removal of an e- reduces repulsion between the remaining e-s and so they a re held closer by the positive charge.
• Anions are bigger than parent atoms, because more e-s will increase shielding, thus outermost e-s feel less effective nuclear charge and held more loosely by the nucleus. Greater repulsion when more e-s are added.

Question 40

Why does ionic radius increase going down a group?

Answer 40

Because higher principle valence shells are introduced to accommodate valence e-s, further from the nucleus.

Question 41

Ion gets larger with increasing coordination number (T/F)

Answer 41

True.

Question 42

Which radius is smaller for when a metal atom or a metal ion?

Answer 42

The ionic radius for the metal ion is smaller than its atomic radius.