Problem 60 - Chemistry: The Central Science

Question

The most common charge associated with scandium in its compounds is 3 +. Indicate the chemical formulas you would expect for compounds formed between scandium and (a) iodine, (b) sulfur, (c) nitrogen.

Step-by-Step Solution

Answer

The chemical formulas for the compounds formed between scandium and (a) iodine, (b) sulfur, and (c) nitrogen are: (a) ScI3, (b) Sc2S3, and (c) ScN.

Step 1: Identify the charges of the other elements

To determine the chemical formulas of the compounds, we need to identify the charges of the other elements when they form compounds. The charges are as follows: (a) Iodine (I): Iodine is a halogen and has a -1 charge in its compounds. (b) Sulfur (S): Sulfur is a chalcogen and forms a -2 charge in its compounds. (c) Nitrogen (N): Nitrogen is a pnictogen and forms a -3 charge in its compounds.

Step 2: Create chemical formulas based on charges

Now, we use the charges to create the chemical formulas of the scandium compounds: (a) Sc 3+ and I -1 : Using the charges, we determine the number of ions needed to balance the charges, which is 3 iodine ions for 1 scandium ion. The chemical formula for the compound formed between scandium and iodine is ScI3. (b) Sc 3+ and S -2 : Using the charges, we determine the number of ions needed to balance the charges, which is 3 sulfur ions for 2 scandium ions. The chemical formula for the compound formed between scandium and sulfur is Sc2S3. (c) Sc 3+ and N -3 : Since both scandium and nitrogen have charges of 3 with different polarities, it balances out and creates a compound with 1 scandium ion and 1 nitrogen ion. The chemical formula for the compound formed between scandium and nitrogen is ScN.

Key Concepts

Ionic Charge

Understanding ionic charge is crucial when predicting chemical formulas of ionic compounds. An ion is an atom or molecule that has gained or lost one or more of its electrons, resulting in a net electrical charge. Positive ions, known as cations, have lost electrons, becoming more positively charged.

For example, the element scandium (Sc) typically forms a cation with a charge of 3+, denoted as Sc³⁺. This means it has lost three electrons. Ionic charge plays a pivotal role in compound formation because it dictates the ratio of ions required for electrical neutrality. In ionic compounds, the total positive charge must balance the total negative charge to result in a neutral compound.

In the given exercise, scandium has a charge of 3+, while iodine (a halogen), sulfur (a chalcogen), and nitrogen (a pnictogen) have charges of 1-, 2-, and 3-, respectively. To determine the chemical formulas, one must combine these ions in ratios where their charges cancel out, leading to a compound that has no overall charge.

Compound Formation

The process of compound formation involves combining different elements in specific ratios to achieve electric neutrality. Elements form compounds to reach a more stable, lower energy state, often by following the octet rule, which states that atoms tend to bond in such a way that each atom has eight electrons in its valence shell.

In ionic compounds, such as those formed by scandium, elements with opposite charges attract. The ratio of combining these elements depends on their ionic charges, as observed with scandium's 3+ charge interacting with iodine, sulfur, and nitrogen, with charges of 1-, 2-, and 3- respectively.

To illustrate, a single Sc³⁺ can pair with three I^- to form ScI₃, as the three iodine ions will balance the charge from one scandium ion. Similarly, two scandium ions will pair with three sulfur ions to achieve charge balance, giving us the compound Sc₂S₃. For nitrogen, a 1:1 ratio with scandium is sufficient, resulting in the compound ScN.

Chemical Nomenclature

Chemical nomenclature is the system of names that chemists use to identify compounds systematically. It involves rules and conventions for naming compounds based on their composition and structure, making it easier for scientists to communicate clearly.

There are different nomenclature systems for inorganic and organic compounds. For ionic compounds like those of scandium and the aforementioned elements, the cation (positive ion) name is given first, followed by the anion (negative ion) name. The anion's name is derived from the element name, typically ending in '-ide'. So, for the scandium compounds discussed:

• ScI₃ is named scandium iodide, because it consists of scandium and iodide (I^-) ions.
• Sc₂S₃ is named scandium sulfide, indicating two scandium ions and three sulfide (S^2-) ions.
• ScN is named scandium nitride, combining a single scandium ion with a nitride (N^3-) ion.

It's vital to learn these naming conventions to understand and communicate chemical identities effectively.