Problem 55 - Chemistry Matter and Change

Question

Explain how an anion of nitrogen forms.

Step-by-Step Solution

Answer

An anion of nitrogen forms by gaining 3 electrons to complete its outer shell, which has 5 valence electrons with an electron configuration of 1s² 2s² 2p³. Nitrogen's valency is 3, and when it gains these electrons, it becomes a negatively charged ion called nitride (N³⁻). In chemical reactions, nitrogen can form nitride by reacting with metals, such as lithium (Li), to produce compounds like lithium nitride (Li₃N).

Step 1: Understand Nitrogen's Electron Configuration

To determine how a nitrogen anion forms, we first look at its electron configuration. Nitrogen (N) has 7 electrons and is in Group 15 of the periodic table. Its electron configuration is 1s² 2s² 2p³, where the outer shell (also called the valence shell) has 5 valence electrons (2 from 2s² and 3 from 2p³).

Step 2: Identify Nitrogen's Valency

To form chemical bonds, nitrogen must either gain or lose electrons to have a full outer shell with 8 electrons (an octet). Nitrogen's valency, or combining capacity, is typically 3 as it can gain 3 more electrons to complete its outer shell (2s² 2p⁶).

Step 3: Gaining Electrons to Form an Anion

An anion is a negatively charged ion that forms when a nonmetal atom gains one or more electrons. In the case of nitrogen, it needs to gain 3 more electrons to complete its outer shell. When nitrogen gains these 3 electrons, it becomes an anion called nitride (N³⁻). The superscript "3⁻" represents the negative charge of the anion due to the gained electrons.

Step 4: Understand How Nitride Forms in a Chemical Reaction

In a chemical reaction, nitrogen can form a nitride anion (N³⁻) by gaining 3 electrons from another element, like metals. For example, reacting lithium (Li) with nitrogen gas (N₂) will produce lithium nitride (Li₃N). In this reaction, nitrogen gains 3 electrons from lithium atoms.

Key Concepts

Electron Configuration

Understanding the electron configuration of an atom is key to grasping how it interacts with other elements. Electron configuration describes the arrangement of electrons around an atom's nucleus. For nitrogen, which is in Group 15 of the periodic table, the configuration is 1s² 2s² 2p³. This tells us that nitrogen has a total of 7 electrons. The first two occupy the 1s orbital, the next two go into the 2s orbital, and the final three are found in the 2p orbital.

Knowing the electron configuration helps us identify the valence electrons, which are crucial for bond formation. For nitrogen, there are 5 valence electrons (2 from 2s² and 3 from 2p³). These valence electrons are the ones involved in chemical reactions, as they are the ones that can be lost, gained, or shared.

Valency

Valency refers to the combining capacity of an atom, indicating how many electrons an atom needs to gain, lose, or share to achieve a stable electron configuration. Most atoms strive to reach the electron configuration of the nearest noble gas, known as the octet rule, which entails having 8 electrons in their valence shell.

For nitrogen, achieving a full outer shell involves gaining three additional electrons. This gives nitrogen a valency of 3. Typically, nitrogen tends to form bonds by sharing or gaining electrons, resulting in a more stable configuration for the atom.

Anion

An anion is an ion with a negative charge, which occurs when an atom gains electrons. For nitrogen, transforming into an anion involves gaining three electrons, which results in the nitride ion, represented as N³⁻. The '3⁻' indicates the three additional electrons gained by the nitrogen atom, giving it a negative charge.

Anions are often formed when nonmetals react with metals. This process leads to metals donating electrons to nonmetals in chemical reactions, creating positively charged cations and negatively charged anions.

Chemical Reactions

Chemical reactions involve the process by which two or more substances interact to form new products. In the context of nitrogen forming an anion, it commonly occurs when nitrogen reacts with a metal. For example, when nitrogen gas (N₂) interacts with lithium (Li), the nitrogen gains electrons from lithium, forming lithium nitride (Li₃N).

During this reaction, each lithium atom donates an electron to nitrogen. This results in the nitrogen atom gaining enough electrons to complete its valence shell. As a result, lithium becomes a positively charged cation, while nitrogen transforms into the negatively charged nitride anion.