Question

Predict the formula of the compound that forms when lithium atoms react with nitrogen atoms. Completely explain your reasoning.

Short answer

The compound formed when lithium atoms react with nitrogen atoms is lithium nitride, with the formula Li_3N. The reasoning behind this is as follows: lithium has one valence electron (Li+) while nitrogen has 5 valence electrons (N3-). To form a neutral compound, three lithium ions (+1 charge each) are needed to balance the charge of one nitrogen ion (-3 charge). Thus, the ratio of lithium to nitrogen ions is 3:1, resulting in the formula Li_3N.

Step-by-step solution

Identify the valence electrons of lithium and nitrogen

First, we need to determine how many electrons are in the outermost shell (valence shell) of a lithium atom and a nitrogen atom by checking the periodic table. Lithium belongs to Group 1, which has one valence electron, while nitrogen belongs to Group 15 (or Group 5A) and has 5 valence electrons.

Determine the charge of the ions formed by each atom

In order to form a stable compound, lithium will likely lose its valence electron to achieve a stable, full outer electron shell (like the noble gas helium). This will result in a lithium ion with a +1 charge (symbolized as Li^+1 or simply Li+). Nitrogen, on the other hand, needs 3 more electrons to reach a stable, full outer electron shell (like the noble gas neon). This means it will likely gain 3 electrons, resulting in a nitrogen ion with a -3 charge (symbolized as N^-3 or simply N3-).

Determine the ratio of lithium ions to nitrogen ions needed to form a neutral compound

To form a neutral compound, the positive charge from the lithium ions must balance the negative charge from the nitrogen ions. Since the lithium ion has a charge of +1 and the nitrogen ion has a charge of -3, we need three lithium ions (3 x +1) to balance the charge of the single nitrogen ion (-3). Therefore, the ratio of lithium ions to nitrogen ions needed to form the compound is 3:1.

Predict the chemical formula of the compound

Based on the ratio of lithium ions to nitrogen ions we found in step 3 (3:1), we can predict the chemical formula of the compound formed between lithium and nitrogen to be Li_3N. This means that there are three lithium atoms reacting with one nitrogen atom to form a neutral compound, lithium nitride, with the formula Li_3N.

Key concepts

Valence Electrons

Valence electrons are the electrons present in the outermost shell of an atom. These electrons play a key role in chemical bonding because they can be gained, lost, or shared during chemical reactions. Understanding the number of valence electrons an atom has can help us determine its reactivity and the types of ions it can form.

For example, lithium, like all Group 1 elements, has one valence electron. This makes it highly reactive, as it tends to lose its one valence electron to achieve a stable, full outer shell similar to the noble gases. Conversely, nitrogen belongs to Group 15 (or Group 5A), with five valence electrons. This means nitrogen needs three additional electrons to attain a stable configuration with a full outer shell.

By recognizing how many valence electrons are present, we can predict how atoms might interact with one another during a reaction. This leads us to our next concept: the formation of ions.

Ions Formation

Ions are charged particles formed when an atom gains or loses electrons. The process aims to achieve a full outer electron shell, leading to greater stability. Atoms can become either positively charged cations or negatively charged anions, depending on whether they lose or gain electrons, respectively.

Lithium, as previously mentioned, tends to lose its one valence electron during a reaction, forming a positively charged cation, Li^+. On the other hand, nitrogen gains three electrons to fill its outer shell, forming a negatively charged anion, N^3-. This transfer and sharing of electrons allow atoms to form ionic compounds that are stable and electrically neutral.

Through understanding ions formation, we get insights into the types of ionic bonds that can form between different elements.

Charge Balance

When ions combine to form a compound, their charges must balance out to maintain electrical neutrality. An ionic compound is stable only when the total positive charge equals the total negative charge. This balancing act necessitates a specific ratio of ions.

In our exercise example, lithium ions (each with a +1 charge) and nitrogen ions (with a -3 charge) must come together in such a way that their charges cancel each other out. To achieve this, three lithium ions are needed to balance the charge of one nitrogen ion. Therefore, the resulting compound must have three lithium ions for every nitrogen ion, creating a 3:1 ratio.

This principle of charge balance is crucial for predicting how different ions combine to form neutral compounds.

Chemical Formulas

Chemical formulas represent the composition of a compound, identifying the elements and the ratio of ions present. The formula is essential for understanding the nature of the compound and its potential chemical behavior.

In the lithium and nitrogen example, a balanced chemical formula reflects the ratio of ions needed for charge neutrality. Hence, with three lithium ions (Li^+) required to balance one nitrogen ion (N^3-), the chemical formula of the compound formed is Li_3N. This indicates that three lithium atoms react with one nitrogen atom to create lithium nitride.

Understanding chemical formulas allows us to predict the properties and reactivity of compounds, serving as a foundational tool in chemistry for studying chemical reactions and interactions.