Formulae Of Ionic Compounds & Their Names: Part 2 | Properties of Matter | Chemistry | FuseSchool

Summary

This lesson teaches the nomenclature and formula derivation of ionic compounds made from polyatomic ions, which consist of more than one atom. Examples of common polyatomic ions like hydroxide, sulfate, nitrate, and others are discussed, along with the 'criss-cross' method to balance charges in formulas. The importance of correctly using brackets to avoid misinterpretation is highlighted through examples. The lesson also touches on the naming of compounds with transition metals, emphasizing the use of Roman numerals to denote their valency.

Takeaways

• 🔬 Ionic compounds can be named and their formulae deduced from the charges of their constituent ions.
• 🌐 Polyatomic ions consist of more than one atom and are different from monatomic ions.
• 📝 Common polyatomic ions include Hydroxide (OH-), Sulphate (SO42-), Nitrate (NO3-), Phosphate (PO43-), Carbonate (CO32-), and Ammonium (NH4+).
• ⚠️ Except for the Ammonium ion, all listed polyatomic ions are anions.
• 📚 Memorizing the formulae and charges of polyatomic ions is essential for understanding ionic compounds.
• 📝 The process of writing ionic compounds involves 'criss-crossing' the charges of the ions to balance them.
• 🧩 In the formula NaNO3, 'Na' stands for sodium and 'NO3' for nitrate, making it sodium nitrate.
• 🔄 The structure of polyatomic ions remains unchanged in ionic compounds, as seen with Mg(OH)2 being magnesium hydroxide.
• 📐 Brackets and subscripts are used to indicate the number of polyatomic ions needed to balance the charge, as in Mg(OH)2.
• 🔄 The formula K2SO4 represents potassium sulphate, with two potassium ions balancing the charge of one sulphate ion.
• 🏷 Transition metals like copper can exhibit multiple valencies, requiring specification in the compound's name, e.g., copper (II) chloride for CuCl2.

Q & A

What is the difference between monatomic and polyatomic ions?

Monatomic ions are ions made of a single atom, while polyatomic ions consist of more than one atom.

What are some common polyatomic ions mentioned in the script?

The common polyatomic ions mentioned are Hydroxide (OH-), Sulphate (SO4^2-), Nitrate (NO3^-), Phosphate (PO4^3-), Carbonate (CO3^2-), and Ammonium (NH4^+).

Why is it important to criss-cross the charges when writing the formula of an ionic compound?

Criss-crossing the charges helps to balance the overall charge of the compound, ensuring that the ionic compound is electrically neutral.

What is the formula for the ionic compound formed by Na+ and NO3- ions?

The formula for the ionic compound formed by Na+ and NO3- ions is NaNO3.

How is the name of the ionic compound NaNO3 derived?

The name 'sodium nitrate' is derived by taking the name of the metal (sodium) and the polyatomic ion (nitrate) as it is.

Why do we use brackets and subscripts in the formula Mg(OH)2 for magnesium hydroxide?

Brackets and subscripts are used to indicate that there are two OH- ions needed to balance the +2 charge of the Mg2+ ion, maintaining the compound's electrical neutrality.

What is the formula and name of the ionic compound formed from K+ and SO4^2- ions?

The formula is K2SO4, and the name is potassium sulphate.

Why is it necessary to specify the valency of transition metals in the name of an ionic compound?

Specifying the valency in the name (e.g., copper (II) chloride) indicates the charge of the transition metal ion and helps distinguish between different compounds that the metal can form.

What does the term 'multivalent' mean in the context of transition metals?

'Multivalent' means that transition metals can form ions with different charges, such as Cu+ or Cu2+ for copper.

How is the valency of a transition metal represented in the name of an ionic compound?

The valency is represented by Roman numerals in round brackets directly after the transition metal, as in 'copper (II) chloride' for CuCl2.

What would be the incorrect formula if OH was not placed in brackets for the compound formed with Mg2+ and OH- ions?

The incorrect formula would be MgOH2, which would imply one oxygen and two hydrogen atoms for each Mg2+ ion, instead of the correct two hydroxide ions.

Outlines

00:00

🧪 Naming and Formulating Ionic Compounds with Polyatomic Ions

This paragraph introduces the concept of polyatomic ions, which are ions composed of more than one atom, in contrast to monatomic ions. It explains the importance of remembering the formulae and charges of common polyatomic ions such as hydroxide, sulfate, nitrate, phosphate, carbonate, and ammonium. The paragraph demonstrates the process of naming and formulating ionic compounds with polyatomic ions through examples, starting with sodium nitrate (NaNO3) and magnesium hydroxide (Mg(OH)2), emphasizing the criss-cross method for balancing charges and the correct representation of polyatomic ions in chemical formulas.

Keywords

💡Ionic Compounds

Ionic compounds are chemical compounds formed by the electrostatic attraction between ions, which are atoms or groups of atoms that have gained or lost electrons. In the video's context, the focus is on how to name and deduce the formulae of these compounds, especially those composed of polyatomic ions. The script provides examples such as NaNO3 and K2SO4 to illustrate the process of formulating ionic compounds.

💡Monatomic Ions

Monatomic ions are ions that consist of a single atom. They have been previously discussed in the context of ionic compounds. The video script introduces polyatomic ions in contrast to monatomic ions, emphasizing the difference in composition and the naming conventions that follow.

💡Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms. The script introduces several common polyatomic ions such as Hydroxide (OH-), Sulphate (SO42-), and Nitrate (NO3-), which are crucial for understanding the formation and naming of ionic compounds in the lesson.

💡Charges

Charges refer to the electrical property of ions, which can be positive or negative, and are a result of the gain or loss of electrons. The script explains how to use the charges of ions to deduce the formulae of ionic compounds through the process of 'criss-crossing,' as seen with the formation of NaNO3 and Mg(OH)2.

💡Criss-Crossing

Criss-crossing is a method used to balance the charges of ions when writing the formula of an ionic compound. The script demonstrates this technique with the examples of sodium nitrate (NaNO3) and magnesium hydroxide (Mg(OH)2), where the charges of the ions are exchanged to achieve a neutral compound.

💡Ammonium Ion

The Ammonium ion (NH4+) is a specific polyatomic ion mentioned in the script. It is unique among the listed polyatomic ions because it is a cation, unlike the others which are anions. Understanding the nature of the Ammonium ion is important for correctly naming and formulating ionic compounds.

💡Anions

Anions are negatively charged ions. The script lists several common anionic polyatomic ions such as Hydroxide, Sulphate, Nitrate, and Phosphate. Recognizing anions is essential for correctly naming and formulating ionic compounds.

💡Cations

Cations are positively charged ions. While the script primarily focuses on anions, it also introduces the Ammonium ion as a cation. Understanding cations is important for balancing the charges in ionic compounds.

💡Transition Metals

Transition metals are elements that can form more than one type of cation with different charges. The script uses Copper (Cu) as an example, which can form Cu+ or Cu2+ ions. The ability of transition metals to exhibit multiple oxidation states is important for naming ionic compounds, as seen with copper (II) chloride.

💡Valency

Valency refers to the combining power of an element, often represented by the charge of the ion it forms. The script explains the importance of specifying the valency of transition metal ions in the names of ionic compounds, such as in 'copper (II) chloride,' where the Roman numeral 'II' indicates the +2 charge of the copper ion.

💡Neutral Charge

A neutral charge means that the overall charge of a compound is zero, with equal numbers of positive and negative charges balancing each other out. The script emphasizes that ionic compounds must be electrically neutral, which is why the formula K2SO4 has two potassium ions (K+) to balance the -2 charge of the sulfate ion.

Highlights

Introduction to naming ionic compounds and deducing their formulae from ionic charges.

Focus on monatomic ions in previous lessons, which are ions made of a single atom.

Transition to learning about polyatomic ions, which consist of more than one atom.

Explanation of the terms 'mono' meaning 'one' and 'poly' meaning 'many' in the context of ions.

Listing of common polyatomic ions including Hydroxide, Sulphate, Nitrate, Phosphate, Carbonate, and Ammonium.

Note on the anionic nature of all listed polyatomic ions except for the Ammonium ion.

Emphasis on memorizing both the formulae and charges of polyatomic ions.

Demonstration of writing and criss-crossing the charges of Na+ and NO3- to form the ionic compound NaNO3.

Naming ionic compounds made from polyatomic ions by writing their names as they are.

Example of forming an ionic compound from Mg2+ and OH- ions, resulting in the formula Mg(OH)2.

Importance of using brackets to denote the correct number of polyatomic ions in a compound.

Explanation of the incorrect formula MgOH2 and its implications for understanding ionic compounds.

Encouragement for students to practice finding the formula and naming ionic compounds on their own.

Example exercise with K+ and SO42- ions, leading to the compound K2SO4, named potassium sulphate.

Understanding the overall neutral charge of ionic compounds and the balancing of charges.

Introduction to transition metals and their ability to form ions with different charges.

Example of naming an ionic compound with a transition metal, copper (II) chloride, formed from Cu2+ and Cl- ions.

Instruction on specifying the valency of transition metals in the name of the compound using Roman numerals.

Transcripts

Previously, we have learned how to name ionic compounds and deduce their formulae from the

ionic charges.

All the ions in the examples provided have one thing in common -- they are made of one

atom, and are therefore known as monatomic ions.

In this lesson, we will learn how to name and deduce the formulae of ionic compounds

made from polyatomic ions.

Polyatomic ions are ions made of more than one atom.

Remember that "mono" means "one", and "poly" means "many".

Common polyatomic ions include: Hydroxide ion: OH-

Sulphate: SO42- Nitrate: NO3-

Phosphate: PO43- Carbonate: CO32-

Ammonium: NH4+ Note that with the exception of the ammonium

ion, all the listed polyatomic ions are anions.

You will have to remember both the formulae and the charges of these polyatomic ions.

Let's grab a piece of paper and a pencil and work on the first example together.

Write the Na+ ion and the NO3- ion side by side -- remember to include the charges!

Let's criss-cross the charges.

Since we never put "one" in a formula, the formula for the ionic compound in question

is NaNO3.

When naming ionic compounds made from polyatomic ions, we just write their names as they are.

The name, therefore, is sodium nitrate.

Now, for our second example, let's write a Mg2+ ion and a OH- ion side by side.

Let's criss-cross the charges.

The structure of the OH- ion does not change when forming an ionic compound -- in this

example, we simply need two OH- ions to balance out the +2 charge of the Mg ion.

This is represented by placing OH in round brackets and the "two" as subscript.

So the formula is Mg(OH)2, and its name is magnesium hydroxide.

If we did not put OH in brackets, we would get MgOH2.

This would mean that for each Mg2+ ion, there is one oxygen atom and two hydrogen atoms,

which is incorrect.

Are you ready to try this on your own now?

Find the formula and name the ionic compound formed from K+ and SO42- ions.

Please pause the lesson to try this, and resume when you are done.

The formula is K2SO4 and the name is potassium sulphate.

Did you get this right?

We know that ionic compounds have an overall neutral charge, so it makes sense to have

two K+ ions to balance the -2 charge of the sulphate ion.

Transition metals are multivalent -- this means that they can form ions with different

charges.

As an example, Cu ions can have either a +1 or +2 charge -- Cu+ or Cu2+.

If we form an ionic compound from Cu2+ and Cl- ions, we must specify the valency of the

Cu ion in its name.

So for CuCl2, the name is copper (II) chloride.

Note that the valency is written as Roman numerals in round brackets directly after

the transition metal.