Chemistry Lesson: Naming Ionic Compounds

Summary

In this lesson from GetChemistryHelp.com, Dr. Kent continues the series on ionic compounds by teaching how to name compounds from their chemical formulas. He explains the difference between fixed charge metals (Type 1) and variable charge metals (Type 2) and demonstrates how to determine the charge of a metal based on the anion in the compound. Using several examples like cobalt nitride, mercury sulfide, and iron nitrate, Dr. Kent shows how to balance the charges and apply the correct nomenclature, providing a deeper understanding of naming ionic compounds.

Takeaways

• 🔢 Ionic compounds generally have metals as the cation, but polyatomic ions like ammonium can also serve as the cation.
• ⚖️ Metals can have fixed or variable charges; fixed-charge metals are called type 1, and variable-charge metals are called type 2.
• 📜 Fixed-charge metals are usually found in groups 1, 2, and a 'Magic Triangle,' including elements like lithium, sodium, and magnesium.
• 🔄 Variable-charge metals (e.g., iron, tin) require a Roman numeral in their names to indicate the specific charge (e.g., Iron(II) or Iron(III)).
• ⚛️ Non-metals gain electrons to match the nearest noble gas configuration, and their names are changed by adding the '-ide' suffix, like nitride or sulfide.
• 🧪 For variable-charge metals, the charge is determined based on the corresponding anion’s charge to balance out the ionic compound.
• ⚗️ Polyatomic ions like nitrate (NO3⁻) and cyanide (CN⁻) must be memorized, as their names don't follow simple naming rules.
• ⚙️ Compounds with fixed-charge metals (e.g., magnesium fluoride) don't need Roman numerals because their charge doesn't vary.
• 🧮 Naming ionic compounds involves balancing the total positive and negative charges, ensuring the formula is neutral overall.
• 🔍 The script covers various examples, demonstrating how to name compounds like mercury(II) sulfide, iron(III) nitrate, and copper(I) oxide.

Q & A

What are ionic compounds typically composed of?

Ionic compounds typically have a metal as the cation. Although 99% of the time it's a metal, they can also have a polyatomic ion like ammonium as the cation.

What is the difference between fixed charge metals and variable charge metals?

Fixed charge metals, also known as Type 1 metals, always have the same charge (e.g., group 1 metals like sodium always have a 1+ charge). Variable charge metals, or Type 2 metals, have charges that can vary (e.g., iron can be 2+ or 3+).

Which metals always have a fixed charge?

Metals in group 1 (e.g., lithium, sodium) always have a 1+ charge, metals in group 2 (e.g., magnesium, calcium) always have a 2+ charge, and metals in the 'Magic Triangle' (aluminum, zinc, and silver) also have fixed charges (aluminum 3+, zinc 2+, silver 1+).

How do we determine the charge of a variable charge metal in a compound?

The charge of a variable charge metal is determined by balancing it with the charge of the anion. For example, if the anion has a 3- charge, the cation must balance it by having an equivalent positive charge.

How is the charge of non-metals determined when they form anions?

Non-metals gain electrons until they reach the electron configuration of noble gases. Non-metals in group 17 gain one electron and have a 1- charge, those in group 16 gain two electrons and have a 2- charge, and those in group 15 gain three electrons and have a 3- charge.

How do we name a compound if the metal has a variable charge?

For variable charge metals, the Roman numeral system is used to indicate the metal's charge in the compound. For example, iron (Fe2+) is named iron(II), and iron (Fe3+) is named iron(III).

What is the naming convention for non-metal anions?

Non-metal anions have their endings changed to '-ide'. For example, when nitrogen becomes an anion, it's named nitride, and when sulfur becomes an anion, it's named sulfide.

How is the charge of an ion in a polyatomic ion determined?

The charge of polyatomic ions must be learned or memorized. For instance, nitrate (NO3) has a 1- charge, while sulfate (SO4) has a 2- charge. These charges are essential for balancing ionic compounds.

How do we name compounds with polyatomic ions?

Compounds with polyatomic ions are named by combining the metal cation's name (with Roman numerals if needed) and the polyatomic ion's name. For example, Fe(NO3)3 is named iron(III) nitrate.

What is the 'Magic Triangle' mentioned in the lesson?

The 'Magic Triangle' refers to three metals that always have fixed charges: aluminum (3+), zinc (2+), and silver (1+). These metals are an exception among transition metals, which typically have variable charges.