Question

The location of an element in the periodic table provides a wealth of information about effective nuclear charge, size, ionization energy, and electron affinity. Using this information, it is possible to predict which elements are more likely to behave as oxidizing agents and which are more likely to behave as reducing agents. Use your knowledge of periodic trends to answer the following questions about the properties you would expect of an element that is a good reducing agent.

a. Zeff : Low or High?

b. Size of Atom: Small or Large?

c. First Ionization Energy: Low or High?

d. Electron Affinity: High Exothermic or Low Exothermic?

Answer 1

As we know, in periodic table, every specfic group and period represents certain properties of elements there are few exceptions as well but majority of the elements show similar trend in physical and chemical properties.

Here in question, reducing character of elements is discussed. To solve this qusetion first one should know the definition of Reducing agents.

Reducing agents or elements are those elements which can donate electrons to other elements during redox reaction and thus itself undegoes oxidation process.

Now, as per periodic table,

Alkaline metals or group I elements donates electron easily because of their lowest Ionization energy.

Expalanation of lowest ionization energy:

The alkali metals posses electronic configuration of the type [Noble gas] ns¹. This nobel gas core shields the outermost electron from nucleus as a result valence electron is loosely held by nucleus and can be removed easily. by supplying small amount of energy. This ionisation energy decreases further down the group.

It means, in group I, Li to Cs the first ionisation energy decreases as extra shells are adding on goind down the group but still Lithium is the most powerful reducing agent than Cesium (Cs).

This is beacuse of the lowest size of Lithium.

Expalnation : Lithium ion undergoes hydration to the maximum extent due to its smallest size. The hydration energy of Li⁺ is maximum and therfeore large amount of heat is released during its hydration. This large amount of energy released during hydration   compensates the energy needed to release electrom from Li atom (I.E.).

Since Group I elements are metals they are unable to attract elctron hence they have very little eletron affinity. This affinity is decreaseing down the group. It means Lithium has high electron affinity. The process of electron acceptance is highly exothermic reaction.

Zeff = Effective Nuclear charge

In case of alkali metals effective nuclear charge is very high. This is because, alakli metal posses [noble gas] ns¹ configuration. During removal of this valence shell electron effective nuclear charge increased and experienced by the remaining electrons.

1s²2s²2p⁶3s¹     1s²2s²2p⁶

Thus the remianing electron are pulled towards nucleus resulting in futher decrease in size. So the combined effect of decrease in number of shell and increse in effective nuclear charge is responsible for the smaller size of alkali metals. So Lithium has the smallest size in the group.

As a summery, for an element to be a good reducing agent

1. Z_eff should be high

2. Size of atom should be low

3. First ionization energy should be low

4. Electron affinity is high exothermic.