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2.3 Structure of Ionic Solids

7 min readdecember 27, 2022

A

Anika P

Dalia Savy

Dalia Savy

A

Anika P

Dalia Savy

Dalia Savy

Atoms come together to make molecules, right? What terms would you use for the two specific atoms that make up an ? The words you use can make or break your FRQ response, so make sure you are careful!

Ionic solids are made up of a positive and a negative . typically occurs when a metal's is transferred to a nonmetal. Since the metal loses a negative electron, it becomes a . On the other hand, since the nonmetal gains a negative electron, it becomes an .

The positive and negative interact because of their opposite charges, but how much they interact depends, again, on .

Structure of Ionic Solids

As mentioned earlier, ionic interactions can produce brittle, hard solids that have high melting points. This is due to the ions being held in a 3-D array known as a

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-7xBMXkhcC02z.png?alt=media&token=0dcc3510-d1f2-4fe4-ab3e-003c4fcff986

The reason for this is that ions are attracted to their opposites, and so negative ions surround positive ones and vice versa. You can think of this arrangement as a way to maximize the attractive forces between the cations and anions while minimizing the repulsive forces.

Another characteristic of this arrangement is how the sizes of the ions generally fit well together. When metals ionize, they lose an electron, making them decrease in size. When nonmetals ionize, they gain an electron, making them increase in size. You could see this periodic trend above with a sodium and chlorine atom ionizing. This allows the small cations (Na+ ions) to fit between the larger anions (Cl- ions). This does not happen for all ionic solids, but it is something to note as it impacts the forces experienced.

Representation of Ionic Solids

It is important to note that for ionic substances look different from that of molecular substances (that have covalent bonds). Covalent substances are usually represented by a molecule (such as H2O) while ionic substances are represented by a network of positive😊 and negative😞 ions.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-T8HY8Z4pP3mz.jpg?alt=media&token=f4701a04-c3e8-45ac-bfbd-bff7bee77aae

Image Courtesy of Principles of General Chemistry; We'll go into this further, but it is good to understand the difference between the two.

Explaining the Lattice Structure

The can be explained by the strong that arise between cations and anions because of their opposing charges. describes these exact forces, telling us that the electrostatic force between a and an is directly proportional to their charges and inversely proportional to the distance between them.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F220px-CoulombsLaw-BMMPBxhxabVB.png?alt=media&token=7bd4dda7-ddcf-430e-80eb-05adc192522f

Image Courtesy of Wikipedia

👉 There is no need to memorize the formula, but if you would like to break it down, check out our study guide on atomic structure and electron configuration.

It is rather important to understand that the strength of these depends on two factors:

  1. Magnitude of charge - The greater the charge of the and , the stronger the attraction between the two.

  2. Distance between the nuclei of the ions - The closer the and , the stronger the attraction between the two.

This is why size is great to note! If the small sodium cations fit between the chloride anions, there is a smaller distance between their nuclei. According to , this increases the strength of attraction between the sodium and chloride ions!

Properties of Ionic Substances

Ionic substances are typically solids at room temperature and are known for their very high melting and boiling points. Let's break down the general properties of ionic substances:

  • 🌡️ High melting and boiling points - The strong that make up an require a lot of energy to overcome, which is why it takes a lot of heat to melt or boil an ionic substance.

  • 🚫🔌Poor as solids - In a lattice, electrons are stuck in place, or in other words, they are localized. Since there are no electrons moving around and carrying an electric current, ionic solids are generally poor conductors of heat and electricity.

  • ⚡Good in their liquid or aqueous states - When ionic solids melt into liquids, their ions are able to move around the liquid phase. In other words, the delocalization of electrons allows them to conduct heat and electricity. This applies to the aqueous phase as well.

  • 💎 Hard and brittle - Ionic solids typically have these characteristics because of their strong . These forces make the ionic solids very difficult to deform.

Lattice Energy

is the energy released when ions bond to form an . We're back to ! It actually relates to too; it's kind of everywhere.

Review of Coulomb's Law

Let's ease into ...do you also remember how to find out which ionic compound would have a higher ? Let's review that, it'll help with I promise!

  1. Out of NaF and NaCl, which one has the higher ?

    First, we would look at the charges of the ions. Here, they are both +1/-1, so charges can't have an effect on the differences in . Then, we would look at which ions are smaller. Remembering the periodic trends, F- is much smaller than Cl-. Since it is smaller, it can be closer to the Na+ ion and increase the strength of attraction. Therefore, it takes more energy to break the bond, increasing the .

If you still don't remember that process, you can review here!

Putting Everything Together

depends on the same two concepts that you used in that question: charge and distance. directly relates to and so just remember:

Easy rule, right? Let's try a few out:

Which of the following compounds has a higher ?

  • NaF or NaCl

    • Since we already thought this question through, it's easy to tell that NaF has the higher .

  • MgO or NaF

    • Charge first: Mg and O have a +2/-2 charge, while Na and F have a +1/-1 charge. You don't even have to check the distance, MgO must have the higher .

  • NaF or KCl

    • Since these ions are in the same groups, they have the same charge. We must remember the and that the farther down in a group you go, the larger the ions get. Therefore, K+ and Cl- are larger than Na+ and F-. With the smaller size, NaF has a higher .

  • LiCl or NaCl

    • Last one! Since Li+ is smaller, LiCl must have a higher .

Check your Understanding

The following question is from the Advanced Placement YT Channel. All credit to them.

Answer the following questions related to Mg and Sr.

  1. Write the complete ground state configuration for the ions Mg+2 and Sr+2.

  2. Do you predict that the ionic radius of Sr+2 is larger or smaller in size than the ionic radius of Mg+2? Justify your answer in terms of atomic structure and the electron configuration of each ion.

  3. The of MgCl2(s) is equal to 2300 kJ/mol. Do you predict that the of SrCl2(s) should be less than or greater than 2300 kJ/mol? Justify your answer in terms of .

Sample Responses

(1) Looking at the periodic table and remembering electron configuration, you should get:

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-wlD6zA9gSVPF.JPG?alt=media&token=58903e33-f830-4aba-8230-8f27e2c048ba

You cannot leave the electron configurations of Mg and Sr as your final answer! Make sure you always answer what they are asking.

I originally wrote down the electron configurations of Mg and Sr and then took off two valence electrons to get the final electron configurations of cations Mg+2 and Sr+2.

(2) This question goes back to . Which ion has more electrons and electron shells? Sr2+ does, so it has a larger ionic radius.

Sample Response: Sr+2 has a larger ionic radius than Mg+2 because it has more occupied electron shells. The valence electrons in Sr2+ are in the 4th energy level whereas the valence electrons in Mg2+ are in the 2nd energy level. Electrons in the 4th energy level are generally farther away from the nucleus, making the ion larger.

(3) Charges are the same, so size must be accountable for the difference in .

Sample Response: states that the higher the charges of the ions and the smaller the distance between the ions, the stronger the attraction and the higher the . Although the charges of Mg+2 and Sr+2 are the same, Sr is a much larger ion due to its greater amount of occupied energy shells. Since it is larger, the distance between Sr+2 and the chlorine ions is greater than the distance between Mg+2 and the chlorine ions. Therefore, the of SrCl2 (s) must be less than 2300 kJ/mol.

Key Terms to Review (16)

Anion

: An anion is an atom or group of atoms that has gained one or more electrons, giving it a negative charge.

Boiling Point

: The boiling point is defined as the temperature at which a liquid changes into vapor under specific atmospheric pressure conditions.

Cation

: A cation is an atom or group of atoms that has lost one or more electrons, giving it a positive charge.

Conductors of Electricity

: Materials that allow electric charges to flow through them easily.

Coulomb's Law

: Coulomb's Law describes the force between two charged objects. It states that this force is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

Crystal Lattice

: A crystal lattice is a symmetrical, three-dimensional arrangement of atoms or ions in a crystal. It's the repeating pattern of particles that forms the solid structure of a crystal.

Delocalization of Electrons

: This refers to electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond.

Electrostatic Forces

: Electrostatic forces are the attractive or repulsive forces between particles that are caused by their electric charges.

Ionic Bonding

: Ionic bonding is a type of chemical bond where one atom transfers one or more electrons to another atom, resulting in positive and negative ions which attract each other.

Ionic Solid

: An ionic solid is a type of crystalline solid composed of ions. These are held together by ionic bonds, which are formed due to the electrostatic attraction between oppositely charged ions.

Lattice Energy

: This is the energy required to break apart an ionic compound and convert its component atoms into gaseous ions.

Lattice Structure

: A lattice structure refers to an orderly arrangement of atoms, ions or molecules in a crystalline material or solid.

Melting Point

: The melting point is the temperature at which a solid will turn into a liquid under standard atmospheric conditions.

Particle Diagrams

: Particle diagrams are visual representations used in chemistry to illustrate the arrangement and interactions of particles in a substance.

Periodic Trends

: Periodic trends are specific patterns that are present in the periodic table that illustrate different aspects of a certain element, including its size and how it bonds with other elements.

Valence Electron

: Valence electrons are the outermost electrons in an atom's electron configuration and have the potential to interact with other atoms. They play a key role in chemical reactions and bonding.

2.3 Structure of Ionic Solids

7 min readdecember 27, 2022

A

Anika P

Dalia Savy

Dalia Savy

A

Anika P

Dalia Savy

Dalia Savy

Atoms come together to make molecules, right? What terms would you use for the two specific atoms that make up an ? The words you use can make or break your FRQ response, so make sure you are careful!

Ionic solids are made up of a positive and a negative . typically occurs when a metal's is transferred to a nonmetal. Since the metal loses a negative electron, it becomes a . On the other hand, since the nonmetal gains a negative electron, it becomes an .

The positive and negative interact because of their opposite charges, but how much they interact depends, again, on .

Structure of Ionic Solids

As mentioned earlier, ionic interactions can produce brittle, hard solids that have high melting points. This is due to the ions being held in a 3-D array known as a

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-7xBMXkhcC02z.png?alt=media&token=0dcc3510-d1f2-4fe4-ab3e-003c4fcff986

The reason for this is that ions are attracted to their opposites, and so negative ions surround positive ones and vice versa. You can think of this arrangement as a way to maximize the attractive forces between the cations and anions while minimizing the repulsive forces.

Another characteristic of this arrangement is how the sizes of the ions generally fit well together. When metals ionize, they lose an electron, making them decrease in size. When nonmetals ionize, they gain an electron, making them increase in size. You could see this periodic trend above with a sodium and chlorine atom ionizing. This allows the small cations (Na+ ions) to fit between the larger anions (Cl- ions). This does not happen for all ionic solids, but it is something to note as it impacts the forces experienced.

Representation of Ionic Solids

It is important to note that for ionic substances look different from that of molecular substances (that have covalent bonds). Covalent substances are usually represented by a molecule (such as H2O) while ionic substances are represented by a network of positive😊 and negative😞 ions.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-T8HY8Z4pP3mz.jpg?alt=media&token=f4701a04-c3e8-45ac-bfbd-bff7bee77aae

Image Courtesy of Principles of General Chemistry; We'll go into this further, but it is good to understand the difference between the two.

Explaining the Lattice Structure

The can be explained by the strong that arise between cations and anions because of their opposing charges. describes these exact forces, telling us that the electrostatic force between a and an is directly proportional to their charges and inversely proportional to the distance between them.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F220px-CoulombsLaw-BMMPBxhxabVB.png?alt=media&token=7bd4dda7-ddcf-430e-80eb-05adc192522f

Image Courtesy of Wikipedia

👉 There is no need to memorize the formula, but if you would like to break it down, check out our study guide on atomic structure and electron configuration.

It is rather important to understand that the strength of these depends on two factors:

  1. Magnitude of charge - The greater the charge of the and , the stronger the attraction between the two.

  2. Distance between the nuclei of the ions - The closer the and , the stronger the attraction between the two.

This is why size is great to note! If the small sodium cations fit between the chloride anions, there is a smaller distance between their nuclei. According to , this increases the strength of attraction between the sodium and chloride ions!

Properties of Ionic Substances

Ionic substances are typically solids at room temperature and are known for their very high melting and boiling points. Let's break down the general properties of ionic substances:

  • 🌡️ High melting and boiling points - The strong that make up an require a lot of energy to overcome, which is why it takes a lot of heat to melt or boil an ionic substance.

  • 🚫🔌Poor as solids - In a lattice, electrons are stuck in place, or in other words, they are localized. Since there are no electrons moving around and carrying an electric current, ionic solids are generally poor conductors of heat and electricity.

  • ⚡Good in their liquid or aqueous states - When ionic solids melt into liquids, their ions are able to move around the liquid phase. In other words, the delocalization of electrons allows them to conduct heat and electricity. This applies to the aqueous phase as well.

  • 💎 Hard and brittle - Ionic solids typically have these characteristics because of their strong . These forces make the ionic solids very difficult to deform.

Lattice Energy

is the energy released when ions bond to form an . We're back to ! It actually relates to too; it's kind of everywhere.

Review of Coulomb's Law

Let's ease into ...do you also remember how to find out which ionic compound would have a higher ? Let's review that, it'll help with I promise!

  1. Out of NaF and NaCl, which one has the higher ?

    First, we would look at the charges of the ions. Here, they are both +1/-1, so charges can't have an effect on the differences in . Then, we would look at which ions are smaller. Remembering the periodic trends, F- is much smaller than Cl-. Since it is smaller, it can be closer to the Na+ ion and increase the strength of attraction. Therefore, it takes more energy to break the bond, increasing the .

If you still don't remember that process, you can review here!

Putting Everything Together

depends on the same two concepts that you used in that question: charge and distance. directly relates to and so just remember:

Easy rule, right? Let's try a few out:

Which of the following compounds has a higher ?

  • NaF or NaCl

    • Since we already thought this question through, it's easy to tell that NaF has the higher .

  • MgO or NaF

    • Charge first: Mg and O have a +2/-2 charge, while Na and F have a +1/-1 charge. You don't even have to check the distance, MgO must have the higher .

  • NaF or KCl

    • Since these ions are in the same groups, they have the same charge. We must remember the and that the farther down in a group you go, the larger the ions get. Therefore, K+ and Cl- are larger than Na+ and F-. With the smaller size, NaF has a higher .

  • LiCl or NaCl

    • Last one! Since Li+ is smaller, LiCl must have a higher .

Check your Understanding

The following question is from the Advanced Placement YT Channel. All credit to them.

Answer the following questions related to Mg and Sr.

  1. Write the complete ground state configuration for the ions Mg+2 and Sr+2.

  2. Do you predict that the ionic radius of Sr+2 is larger or smaller in size than the ionic radius of Mg+2? Justify your answer in terms of atomic structure and the electron configuration of each ion.

  3. The of MgCl2(s) is equal to 2300 kJ/mol. Do you predict that the of SrCl2(s) should be less than or greater than 2300 kJ/mol? Justify your answer in terms of .

Sample Responses

(1) Looking at the periodic table and remembering electron configuration, you should get:

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-wlD6zA9gSVPF.JPG?alt=media&token=58903e33-f830-4aba-8230-8f27e2c048ba

You cannot leave the electron configurations of Mg and Sr as your final answer! Make sure you always answer what they are asking.

I originally wrote down the electron configurations of Mg and Sr and then took off two valence electrons to get the final electron configurations of cations Mg+2 and Sr+2.

(2) This question goes back to . Which ion has more electrons and electron shells? Sr2+ does, so it has a larger ionic radius.

Sample Response: Sr+2 has a larger ionic radius than Mg+2 because it has more occupied electron shells. The valence electrons in Sr2+ are in the 4th energy level whereas the valence electrons in Mg2+ are in the 2nd energy level. Electrons in the 4th energy level are generally farther away from the nucleus, making the ion larger.

(3) Charges are the same, so size must be accountable for the difference in .

Sample Response: states that the higher the charges of the ions and the smaller the distance between the ions, the stronger the attraction and the higher the . Although the charges of Mg+2 and Sr+2 are the same, Sr is a much larger ion due to its greater amount of occupied energy shells. Since it is larger, the distance between Sr+2 and the chlorine ions is greater than the distance between Mg+2 and the chlorine ions. Therefore, the of SrCl2 (s) must be less than 2300 kJ/mol.

Key Terms to Review (16)

Anion

: An anion is an atom or group of atoms that has gained one or more electrons, giving it a negative charge.

Boiling Point

: The boiling point is defined as the temperature at which a liquid changes into vapor under specific atmospheric pressure conditions.

Cation

: A cation is an atom or group of atoms that has lost one or more electrons, giving it a positive charge.

Conductors of Electricity

: Materials that allow electric charges to flow through them easily.

Coulomb's Law

: Coulomb's Law describes the force between two charged objects. It states that this force is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

Crystal Lattice

: A crystal lattice is a symmetrical, three-dimensional arrangement of atoms or ions in a crystal. It's the repeating pattern of particles that forms the solid structure of a crystal.

Delocalization of Electrons

: This refers to electrons in a molecule, ion or solid metal that are not associated with a single atom or a covalent bond.

Electrostatic Forces

: Electrostatic forces are the attractive or repulsive forces between particles that are caused by their electric charges.

Ionic Bonding

: Ionic bonding is a type of chemical bond where one atom transfers one or more electrons to another atom, resulting in positive and negative ions which attract each other.

Ionic Solid

: An ionic solid is a type of crystalline solid composed of ions. These are held together by ionic bonds, which are formed due to the electrostatic attraction between oppositely charged ions.

Lattice Energy

: This is the energy required to break apart an ionic compound and convert its component atoms into gaseous ions.

Lattice Structure

: A lattice structure refers to an orderly arrangement of atoms, ions or molecules in a crystalline material or solid.

Melting Point

: The melting point is the temperature at which a solid will turn into a liquid under standard atmospheric conditions.

Particle Diagrams

: Particle diagrams are visual representations used in chemistry to illustrate the arrangement and interactions of particles in a substance.

Periodic Trends

: Periodic trends are specific patterns that are present in the periodic table that illustrate different aspects of a certain element, including its size and how it bonds with other elements.

Valence Electron

: Valence electrons are the outermost electrons in an atom's electron configuration and have the potential to interact with other atoms. They play a key role in chemical reactions and bonding.


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AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.


© 2024 Fiveable Inc. All rights reserved.

AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.