Properties And Reactions Of Elements And Compounds of P Block Elements - Session 2

As we know, in a chemical reaction, the loss of one or more electrons by an atom, molecule or ion is called oxidation. While the gain of one or more electrons by an atom, molecule or ion is called reduction.For example, when oxygen reacts with Magnesium, Magnesium oxide is formed. Oxidation state of oxygen changes from zero to negative two. This shows oxygen gains two electrons from Magnesium. Oxygen has undergone reduction. Similarly, Magnesium loses two electrons. Magnesium has undergone reduction.

Oxidizing ability refers to the ability of a substance to oxidize another substance by accepting electrons from it. In other words, it is the ability of a substance to cause oxidation in another substance. A substance that oxidizes other substance is called oxidizing agent. The Oxidizing agent itself undergoes reduction. For example, the reaction between iron and oxygen can be used to explain oxidizing ability. In this reaction, iron loses electrons and oxygen gains electrons. Oxygen is the oxidizing agent because it causes oxidation in iron.

P block elements can exhibit different oxidizing abilities depending on their electronic configuration and atomic size. For example, Oxygen has a high electronegativity and a small atomic size. It can easily accept electrons from other elements, making it a strong oxidizing agent. In the reaction between oxygen and Hydrogen oxygen accepts electrons from Hydrogen to form water. It is therefore the oxidizing agent.

After oxygen, the P block element Chlorine has a high electronegativity. It has a small atomic size, similar to oxygen. It can also easily accept electrons, making it a strong oxidizing agent. For example, in the reaction between Chlorine and iron, the oxidation state of Chlorine changes from zero to negative one. Chlorine accepts electrons from iron to form iron chloride. It oxidizes iron. It is therefore an oxidizing agent.

The P block element Nitrogen has a moderate electronegativity and a larger atomic size compared to oxygen and Chlorine. It can also act as an oxidizing agent, but not as strong as oxygen and Chlorine.For example, in the reaction between nitrogen and Hydrogen, nitrogen accepts electrons from Hydrogen to form ammonia. Oxidation state of nitrogen changes from zero to negative three. It is therefore an oxidizing agent.

The oxidizing ability of P blockelements generally decreases downward in a group, because the atomic size increases and the electronegativity decreases. Due to decrease in electronegativity, these elements are less likely to accept electrons. Therefore they are less likely to act as oxidizing agents. However, the oxidizing ability generally increases across a period from left-to-right, because the atomic size decreases and the electronegativity increases. This means that these elements are more likely to accept electrons and act as oxidizing agents.

Reducing ability refers to the ability of a substance to reduce another substance by donating electrons to it. In other words, it is the ability of a substance to cause reduction in another substance. The substance that causes reduction in other substance and itself undergoes oxidation is called reducing agent.For example, when carbon reacts with oxygen, it forms carbon Dioxide. The oxidation state of carbon changes from zero to positive four. It undergoes oxidation. Carbon reduces the oxygen.

P blockelements can exhibit different reducing abilities depending on their electronic configuration and atomic size. Boron has a low electronegativity and a small atomic size, which allows it to easily donate electrons and act as a reducing agent. For example, in the reaction between Boron and fluorine, Boron donates electrons to fluorine to form Boron Trifluoride. Oxidation state of Boron changes from zero to positive three. Boron reduces the fluorine. Boron is a good reducing agent.

The P block element Silicon has a moderate electronegativity and a larger atomic size compared to Boron. This makes it a weaker reducing agent. For example, in the reaction between silicon and Chlorine, Silicon donates electrons to Chlorine to form silicon tetrachloride. Oxidation state of silicon changes from zero to positive four. Silicon reduces Chlorine. Silicon is therefore the reducing agent.

The reducing ability of P block elements generally increases downward in a group, because the atomic size increases and the electronegativity decreases. This means that these elements are more likely to donate electrons and act as reducing agents. However, the reducing ability generally decreases across a period from left-to-right, because the atomic size decreases and the electronegativity increases. This means that these elements are less likely to donate electrons and act as reducing agents.

Here’s a fascinating fact. Some compounds of P blockelements, act both as oxidizing agents and reducing agents. For example, when Hydrogen Sulfide reacts with metals such as copper, it acts as oxidizing agent. The product of this reaction is copper Sulfide and Hydrogen gas. Hydrogen Sulfide oxidizes the copper. The Oxidation state of copper changes from zero to positive two.

Hydrogen Sulfide also acts as reducing agent when it is reacted with Potassium permanganate or Potassium dichromate. Hydrogen Sulfide reduces Potassium permanganate and itself undergoes oxidation. Oxidation state of Sulfur changes from negative two to zero. This shows that Hydrogen Sulfide undergoes oxidation. Oxidation state of Manganese changes from positive seven to positive two. This shows that Potassium permanganate undergoes reduction. We can say that Hydrogen Sulfide reduces Potassium Permanganate and acts as a reducing agent.

Sulfur Dioxide acts as a reducing agent when it reacts with halogens. For example, when Sulfur Dioxide reacts with Chlorine, it forms Sulfuric acid and hydrochloric acid. Oxidation state of Sulfur changes from positive four to positive six. This means Sulfur Dioxide undergoes oxidation. Oxidation state of Chlorine changes from zero to negative one. This means Chlorine has undergone reduction. This shows that Sulfur Dioxide reduces the Chlorine, and itself undergoes oxidation. So Sulfur Dioxide acts as a reducing agent here.

When Sulfur Dioxide reacts with metals, it acts as an oxidizing agent. For example, when Sulfur Dioxide reacts with Magnesium metal, it forms Magnesium Oxide and Sulfur. Oxidation state of Sulfur changes from +4 to 0. Meanwhile the oxidation state of Magnesium changes from 0 to +2. This shows that Sulfur Dioxide accepts electrons from Magnesium and oxidizes Magnesium. So Sulfur Dioxide acts as an oxidizing agent.

The Disproportionation property is a unique characteristic of p-block elements. It involves the oxidation and reduction of the same element in a single chemical reaction. In this process, one atom of an element undergoes both oxidation and reduction simultaneously, producing two different oxidation states of that element.This property is particularly common in group 15, group 16 and group 17 elements, such as Nitrogen, Phosphorus, Chlorine, Bromine, Arsenic, Antimony, Sulfur, Selenium, and Tellurium. These elements have a tendency to exist in multiple oxidation states, making them capable of undergoing disproportionation reactions.

For example, consider the reaction of Chlorine Dioxide ClO₂ with water H₂O to form HClO₃ and HCl. In this reaction, Chlorine in the ClO₂ molecule is simultaneously oxidized from a +4 to a +5 oxidation state in HClO₃. Meanwhile it is reduced from +4 Oxidation state in ClO₂ to -1 oxidation state in HCl.

Similarly, nitrogen can undergo disproportionation reactions. It is seen here in the reaction of NH3 with Chlorine Gas. In this reaction, Nitrogen is oxidized from -3 oxidation state in NH3 to zero oxidation state in Nitrogen. It is also reduced from +3 oxidation state in NH₃ to -1 oxidation state in NH₄Cl.

Amphiprotic substances are molecules or ions that can act as both acids and bases by donating and accepting a proto. In other words, donating an H⁺ ion. Examples of amphiprotic substances include water ,amino acids and HCO₃⁻ ion.Water can act as an acid by donating an H⁺ to a strong base. Thus, forming a Hydronium ion, written as H3O⁺ ion. It can also act as a base by accepting an H⁺ from a strong acid, forming a Hydroxide Ion OH- ion.