Unit B Lesson 8: Ionic Compounds
Completion requirements
Unit B Lesson 8: Ionic Compounds
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Learning Targets |
Big Question: How do I name and write formulas for ionic compounds?
We use chemicals for many purposes at school, at home, and at work. It is your responsibility to make sure you know how to work with each chemical safely.
We use chemicals for many purposes at school, at home, and at work. It is your responsibility to make sure you know how to work with each chemical safely.
At the end of this inquiry, you should be able to answer the following questions:
- What is an ion
- What is a cation?
- What is an anion?
- What is an ionic compound?
- How is an ionic compound formula written?
- What is a superscript?
- How is an ionic compound named?
- What are four properties of ionic compounds?
Page 144 to 147 in your text will help you answer these questions about ionic compounds.
Periodic Table links:
Introduction
Ionic Compounds
Ionic compounds are chemical substances that exist in more than chemical laboratories. We can find them easily in the world around us. In this lesson, you will learn to identify ionic compounds, name ionic compounds, and write ionic formulas.
Ionic compounds are chemical substances that exist in more than chemical laboratories. We can find them easily in the world around us. In this lesson, you will learn to identify ionic compounds, name ionic compounds, and write ionic formulas.
Sodium chloride, NaCl, is table salt. NaCl is made up of Na+ and Cl– ions.
Sodium fluoride, NaF, is added to toothpaste and tap water to help strengthen tooth enamel.
Calcium carbonate, CaCO3, is found in nature in seashells, egg shells, and limestone.
Ammonium nitrate, (NH4NO3), can be used to fertilize plants.
Ionic compounds are made up of ions. In Lesson 4, you learned that electrons have a negative charge. An ion is an atom that has a charge because it has lost or gained electrons.
All ion charges can be seen in the top right-hand corner of the element symbol in the periodic table. The charge of an ion is always placed to the upper right of the element symbol. For example, the charge of a calcium ion is +2 or 2+. This means the calcium ion loses two electrons.
Every ionic compound is produced from one or more positive ions and one or more negative ions. The positive and negative ions join together in a way that makes the final compound have a neutral charge. In other words, when you add up all of the positive and negative charges on the ions in an ionic compound, they must add up to zero.
All ion charges can be seen in the top right-hand corner of the element symbol in the periodic table. The charge of an ion is always placed to the upper right of the element symbol. For example, the charge of a calcium ion is +2 or 2+. This means the calcium ion loses two electrons.
Every ionic compound is produced from one or more positive ions and one or more negative ions. The positive and negative ions join together in a way that makes the final compound have a neutral charge. In other words, when you add up all of the positive and negative charges on the ions in an ionic compound, they must add up to zero.
Watch
Watch this video to learn more about ions and ionic compounds.
Cations
A neutral metal atom (left of the staircase line) that has lost electrons becomes positive and is called a cation. The resulting ion (cation) is positive because the number of protons in the nucleus of the atom is greater than the number of electrons surrounding the atom.
The cation name is the same as the element name. It is always written first in the name of any compound it is in. Here are some examples of cations:
A neutral metal atom (left of the staircase line) that has lost electrons becomes positive and is called a cation. The resulting ion (cation) is positive because the number of protons in the nucleus of the atom is greater than the number of electrons surrounding the atom.
The cation name is the same as the element name. It is always written first in the name of any compound it is in. Here are some examples of cations:
| Element Name
|
Neutral Atom
|
Cation | Cation Name
|
| Sodium | Na | Na+ | Sodium |
| Magnesium | Mg |
Mg2+
|
Magnesium |
| Gallium | Ga | Ga3+ | Gallium |
Anions
A non-metal atom (right of the staircase line) that gains electrons is negative and is called an anion. The non-metal ion is negative because there are more electrons surrounding the atom than there are protons in the nucleus. Therefore, the overall charge becomes negative.
The anion name is changed from the element name. The ending of the element name changes to -ide. The anion is always written after the cation in the name of any compound it is in. Here are some examples of anions:
A non-metal atom (right of the staircase line) that gains electrons is negative and is called an anion. The non-metal ion is negative because there are more electrons surrounding the atom than there are protons in the nucleus. Therefore, the overall charge becomes negative.
The anion name is changed from the element name. The ending of the element name changes to -ide. The anion is always written after the cation in the name of any compound it is in. Here are some examples of anions:
| Element Name
|
Neutral Atom
|
Anion | Anion Name
|
| Chlorine | Cl | Cl– | Chloride |
| Selenium | Se | Se2- | Selenide |
| Nitrogen | N |
N3–
|
Nitride |
Note: An atom can never lose or gain protons. An atom can lose or gain only electrons.
Most ionic compounds follow similar rules when they form from cations and anions:
- Salt, NaCl, is an ionic compound.
- Na+ (positive metal cation) combines with Cl– (negative non-metal anion) to form salt.
- One Na+ cation and one Cl– anion join to form a neutral charged NaCl.
- Notice the crystal structure of NaCl. All ionic compounds form crystals in patterns like this.
- The name of the ionic compound formed between the ions of sodium and chlorine is "sodium chloride".
Watch
Watch "Atoms vs. Ions" to find how ions are formed.
Watch
Properties of Ionic Compounds
As you watch the following videos, try to make a list of four properties of ionic compounds. You can check your answers just below the second video.
As you watch the following videos, try to make a list of four properties of ionic compounds. You can check your answers just below the second video.
Read pages 144 and 145 in Science in Action 9.
Four Properties of Ionic Compounds
- Solid crystals at room temperature
- High melting and boiling points
- Brittle
- Conduct electricity (when dissolved in water or in liquid form)
Naming Ionic Compounds
Ionic compounds form when electrons are transferred from a metal atom to a non-metal. As a result, the metal forms a positively charged ion called a cation. The non-metal forms a negatively charged ion called an anion. Every ionic compound contains one type of metal ion and one type of non-metal ion. See how electron transfer occurs in "Ionic Compound Formation" and "Ionic Bond".
Ionic compounds form when electrons are transferred from a metal atom to a non-metal. As a result, the metal forms a positively charged ion called a cation. The non-metal forms a negatively charged ion called an anion. Every ionic compound contains one type of metal ion and one type of non-metal ion. See how electron transfer occurs in "Ionic Compound Formation" and "Ionic Bond".
When naming ionic compounds, you must locate the metal ion and the non-metal ion on the periodic table.
When naming ionic compounds, follow these steps:
- Metals are to the left of the staircase line. In the periodic table on pages 126 to 127 in Science in Action 9, metals are green.
- Non-metals are to the right of the staircase line. In the periodic table on pages 126 and 127 in Science in Action 9, non-metals are orange.
When naming ionic compounds, follow these steps:
For example: What is the chemical name for NaCl?
- Step 1: The metal ion (cation) is always written first.
- Step 2: The non-metal ion (anion) is always written second. Change the suffix (ending) of the non-metal ion to “ide”.
- The metal ion is called "sodium"
- The non-metal ion is formed from the chlorine atom. When chlorine gains an electron and forms an ion, the ending is changed to "ide" — the ion is called "chloride".
- Therefore, the name for NaCl is sodium chloride.
Watch
Watch these videos to solidify your knowledge of naming ionic compounds.
Summary of Naming Ionic Compounds
metal ion + non-metal ion = ionic compound
calcium + bromide = calcium bromide
magnesium + oxide = magnesium oxide
metal ion + non-metal ion = ionic compound
calcium + bromide = calcium bromide
magnesium + oxide = magnesium oxide
Try It!
Practice Worksheet: Naming Ionic Compounds: Part 1
- DOWNLOAD the practice worksheet (S9_UB_S3_L8a_ionic_compounds1). If you prefer to use a Google Drive or PDF version of the worksheet, click here.
-
Complete the practice worksheet.
-
When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!
Watch
Watch the following videos to better understand the role of ionic charge in the formation of ionic compounds.
Try It!
Practice Worksheet: Overall Charge of Every Ionic Compound is Neutral
-
DOWNLOAD the practice worksheet (S9_UB_S3_L8b_ionic_compounds_neutral). If you prefer to use a Google Drive or PDF version of the worksheet, click here.
-
Complete the practice worksheet.
- When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
Wait! Don't view the suggested answers first.
This practice work is not for marks, it is meant to help you check your
understanding. Check the answers AFTER doing the questions! Keep the
practice worksheet for study purposes. If you don't understand
something, contact your teacher!
Note: Answers are out of order, but they are all there, check your work carefully.
Writing Ionic Compound Formulas
When writing the names of ionic compounds, you must locate the metal ion and the non-metal ion on the periodic table.
When writing the names of ionic compounds, follow these steps:
Example:
What is the chemical formula of the ionic compound calcium fluoride?
- Metals are to the left of the staircase line. In the periodic table on pages 126 to 127 in Science in Action 9, metals are green.
- Non-metals are to the right of the staircase line. In the periodic table on pages 126 and 127 in Science in Action 9, non-metals are orange.
When writing the names of ionic compounds, follow these steps:
- Write the symbols.
- Write the charges.
- Balance the ions so the net charge is zero.
- Write the chemical formula, removing all charges.
- Check that the charges balance, and the compound is neutral.
Example:
What is the chemical formula of the ionic compound calcium fluoride?
1. Write the symbols.
2. Write the charges.
3. Balance the ions so the net charge is zero.
4. Write the chemical formula, removing all charges.
5. Check that the charges balance, and the compound is neutral.
2. Write the charges.
3. Balance the ions so the net charge is zero.
4. Write the chemical formula, removing all charges.
5. Check that the charges balance, and the compound is neutral.
Ca F
Ca2+ F–
Ca2+ F– F–
CaF2
(+2) + (–1) + (–1) = 0
(+2) + (–1) + (–1) = 0
Watch
Watch how to write the chemical formula for the ionic compound calcium fluoride.
Try these examples of writing chemical formulas for ionic compounds. Each example has a video explanation.
- K2S
- RbI
- Sr3P2
- AlBr3
Watch these videos for more practice:
Writing Ionic Formulas
Formulas Lesson 1: Writing Formulas for Binary Ionic Compounds
Writing a Chemical Formula for Ionic Compounds
Example 1
Write the chemical formula for lithium oxide.
Step 1
Find both elements, from the information given in the chemical name, on the periodic table. The positive ion (written first) will be a metal (left of the staircase line) and the negative ion (written second) will be a non-metal (right of the staircase line).
Step 2
Write the charge of both ions. The metal ion is positive. The non-metal ion is negative.
Li + is the symbol for the lithium ion. O2– is the symbol for the oxide ion.
Step 3
Do the charges balance? (Is the number of positive charges equal to the number of negative charges?)
If the charges do not balance, you have three options:
Initially, the formula has one Li+ and one O2– . The net charge is
Does total positive charge + total negative charge = 0?
If the answer is NO, add another ion.
If the answer is YES, move to the next step.
Step 4
Write the chemical formula, removing all charges. Use subscripts to identify the number of each type of atom.
Li 2O
Step 5
Check the charges.
Write the chemical formula for lithium oxide.
Step 1
Find both elements, from the information given in the chemical name, on the periodic table. The positive ion (written first) will be a metal (left of the staircase line) and the negative ion (written second) will be a non-metal (right of the staircase line).
- The metal is Li and the non-metal is O. (Oxygen becomes “oxide” when it has a charge and forms an ion.)
Step 2
Write the charge of both ions. The metal ion is positive. The non-metal ion is negative.
Li + is the symbol for the lithium ion. O2– is the symbol for the oxide ion.
Step 3
Do the charges balance? (Is the number of positive charges equal to the number of negative charges?)
If the charges do not balance, you have three options:
- Add more positive ions.
- Add more negative ions.
- Add both positive and negative ions.
Initially, the formula has one Li+ and one O2– . The net charge is
Adding an additional “+1” charge (Li+) produces a net charge ofLi + O2–
(+1) + (–2) = (-1)
Are the charges balanced?Li + Li+ O2–
(+1) + (+1) + (–2) = 0.
Does total positive charge + total negative charge = 0?
If the answer is NO, add another ion.
If the answer is YES, move to the next step.
Step 4
Write the chemical formula, removing all charges. Use subscripts to identify the number of each type of atom.
Li 2O
- The two indicates that there are two Li+ ions. O does not have a subscript, so there is one ion of O2– .
Step 5
Check the charges.
Li + Li+ O2–
(+1) + (+1) + (–2) = 0
Example 2
Write the chemical formula for gallium chloride.
Step 1
Find both elements, from the information given in the chemical name, on the periodic table. The positive ion (written first) is a metal (left of the staircase line) and the negative ion (written second) is a non-metal (right of the staircase line).
Step 2
Write the charge of both ions. The metal ion is positive. The non-metal ion is negative.
Ga 3+ is the symbol for the gallium ion. Cl– is the symbol for the chloride ion
Step 3
Do the charges balance? (Is the number of positive charges equal to the number of negative charges?)
If the charges do not balance, you have three options:
Initially, in one Ga3+ and one Cl–, the net charge is:
Does total positive charge + total negative charge = 0?
If the answer is NO, add another ion.
If the answer is YES, move to the next step.
Step 4
Write the chemical formula, removing all charges. Use subscripts to identify the number of each type of atom.
GaCl 3
Check the charges.
Write the chemical formula for gallium chloride.
Step 1
Find both elements, from the information given in the chemical name, on the periodic table. The positive ion (written first) is a metal (left of the staircase line) and the negative ion (written second) is a non-metal (right of the staircase line).
- The metal is Ga and the non-metal is Cl. (Chlorine becomes “chloride” when it has a charge and forms an ion.)
Step 2
Write the charge of both ions. The metal ion is positive. The non-metal ion is negative.
Ga 3+ is the symbol for the gallium ion. Cl– is the symbol for the chloride ion
Step 3
Do the charges balance? (Is the number of positive charges equal to the number of negative charges?)
If the charges do not balance, you have three options:
- Add more positive ions.
- Add more negative ions.
- Add both positive and negative ions.
Initially, in one Ga3+ and one Cl–, the net charge is:
Ga 3+ Cl–
(+3) + (-1) = (+2)
Because the charge is +2, two additional “-1” charges (Cl-) can be added. Then, the net charge is
Are the charges balanced?Ga3+ Cl– Cl– Cl–
(+3) + (–1) + (–1) + (–1) = 0
Does total positive charge + total negative charge = 0?
If the answer is NO, add another ion.
If the answer is YES, move to the next step.
Step 4
Write the chemical formula, removing all charges. Use subscripts to identify the number of each type of atom.
GaCl 3
- Ga does not have a subscript, so there is one ion of Ga3+ .
- The three indicates that there are three Cl– ions.
Check the charges.
Ga+3 Cl– Cl– Cl–
(+3) + (–1) + (–1) + (–1) = 0
Summary for writing chemical formulas for ionic compounds:
- Write symbols.
- Write charges.
- Balance ions so net charge is zero.
- Write the formula removing all charges.
- Check
Practice Activity
Practice Worksheet: Writing Ionic Formulas Part 1
(Part 2 appears in the next lesson)
(Part 2 appears in the next lesson)
- DOWNLOAD this practice worksheet (S9_UB_S3_L8c__ionic_formulas1). If you prefer to use a Google Drive or PDF version of the worksheet, click here.
- Complete the practice worksheet. Write the chemical formula for each ionic compound name. The first five compounds are video examples if you wish to view them.
-
When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.
Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!
