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2.2 Intramolecular Force and Potential Energy

6 min readdecember 26, 2022

A

Anika P

Dalia Savy

Dalia Savy

A

Anika P

Dalia Savy

Dalia Savy

You may be thinking, what are ? are the forces between two atoms in a molecule! This is very different from intermolecular forces, which we learn in unit three.

💡 Intramolecular and are often confused, so here are some tips:

  • Intermolecular forces are those between molecules. Think inter = between two groups

  • Intramolecular forces are those between two groups in a molecule, so think intra = within a group.

So far, we learned about two intramolecular forces: and .

👉 For a review of what ionic bonds and covalent bonds are, as well as how to distinguish between the two, check out the linked study guide about the types of chemical bonds.

Potential Energy and Bonding

You may wonder where fits into bonding. Well, remember how chemistry favors and always strives to reach the highest stability? The lower the of a bond, the more stable it is! This is a fundamental rule you should try to keep in the back of your mind when learning about the strength and formation of bonds.

Because of this connection, physical or chemical processes can be described through energy diagrams. A graph of versus the distance between atoms is a useful tool for understanding the interactions between atoms. Taking a look at this graph, you can see several things:

  1. The "" - basically another phrase for the distance between atoms where is at its lowest point. Let's simplify it even more: the distance at which the atoms are the most stable.

  2. The - the amount of energy necessary to separate two atoms in a bond. This can be calculated or conceptually thought of as the difference in between the separated atoms and the atoms at their , or most stable phase.

  3. The strength of the bond - this can be grasped from the . In general, bonds with higher bond energies are stronger and more stable, while bonds with lower bond energies are weaker and less stable.

  4. The length of the bond, or the physical distance between the two atoms bonded to one another.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-2c55nRKO7lsX.png?alt=media&token=e065e03b-92f0-4887-a293-785cd65d3f9e

Image Courtesy of Stack Exchange

Potential Energy and Covalent Bonds

In molecular compounds with , the is influenced by both the size of the atoms and the .

is another term for how bonds can either be classified as single, double, or triple bonds.

Electrons Involved in Bond
(-)Two electronsLongestSmallest
(=)Four electronsMiddleMiddle
(≡)Six electrons ShortestLargest

An easy way to remember the number of electrons involved in a bond is that each dash on a lewis dot diagram corresponds to two shared electrons.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-POKnM2fBfVrB.gif?alt=media&token=54e6fe2e-bce5-4037-9f77-67fab496fbae

Image Courtesy of Shodor

Since bonds with higher bond energies are stronger and more stable, triple bonds are generally the most stable. This makes them the most difficult to break. However, it is important to note that stability also depends on other factors such as the size and charge of the atoms involved. Let's try and put some of this information together and take a look at a graph of .

Breaking Down a Potential Energy Diagram

For , the is influenced by the (single, double, triple) and the balance between repulsive and attractive forces. in the diagram shows how the greatest is the of two atoms. 

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-OMaXj4F3Hi3P.png?alt=media&token=5eadddef-db77-4cf7-ab1e-46eb90cd0341

Image Courtesy of SplainScience

Let's take a look at each of these stages:

  • - Since the atoms are very close together and the is very small, the atoms are experiencing lots of electron-electron . This causes the bond to be very unstable and leads to a of greater than zero.

  • Some overlap/ - This is the most stable state and the at this point is what we referred to as the "." There is a balance⚖️ between the repulsive and attractive forces and a stable bond is formed. Hopefully, now you understand why is lowest when the bond is stable.

    • The at this stage is the amount required to break the bond or the .

  • No overlap/ - Since the is so large, there are no interactions between the two atoms, and no bond is formed. This leads to a of almost zero.

Example with PE Diagrams

It is good to understand these properties because you may be asked to guess where an element falls on this graph.

Say the following image is a diagram of chlorine atoms bonded together (Cl-Cl). Where would Br-Br fall in comparison to chlorine's curve?

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-PvlVC0eJi3kI.png?alt=media&token=4fc580e8-9ba4-4054-83b0-0b24183fba7d

Image Courtesy of Chegg

To answer this question, we have to think about periodic trends and take a look at the axes of this graph:

  • : is the Cl-Cl bond or Br-Br bond longer? Well, the bond between the atoms with larger atomic radii would have to be the longer one. As you go down in a group on the periodic table, the atomic radius increases. Since bromine is below chlorine on the periodic table, the Br-Br bond is longer than the Cl-Cl bond.

    • This tells you where to draw the Br-Br curve in relation to the x-axis.

  • : which bond would be easier to break? Cl-Cl or Br-Br? This should automatically make you think of ionization energy. The lower the ionization energy, the easier it would be to break the bond. As you go down a group, ionization energy decreases because there are more occupied electron shells and the nucleus' with the valence electrons is weakest. Therefore, bromine has a lower ionization energy and the Br-Br bond is much easier to break.

    • This tells you where to draw the Br-Br curve in relation to the y-axis.

Knowing that the Br-Br bond is longer and easier to break, you would have to graph its curve up (less energy) and to the right more (larger ).

This question is a very good way to test your knowledge about this key topic and periodic trends. Here is what the graph should look like:

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-iOhbX69sGZzN.JPG?alt=media&token=62501919-d66b-4a6d-80fa-2a8014e22c17

Forces Within Ionic Bonds

Understanding the strength of ionic interactions involves the use of Coulomb's Law.

As we went over in the previous unit, you do not need to know the formula. However, you are expected to understand what conceptually means.

Essentially, the energy of two interacting charged particles (ions) depends on the magnitude of charge and the distance between the nuclei of the two particles.

  • The greater the charge of the atoms, the stronger the . This is because the more positively charged a nucleus is, the more strongly it can attract electrons toward it.

  • The closer the two particles are to each other, the stronger the . Think about it this way: magnets are not attracted to each other if they are placed 3 feet apart. They need to be close to feel the . 🧲

Smaller and highly charged ions have the strongest interactions, according to .

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-fTUXSu67u4ay.png?alt=media&token=9039b6ff-ee53-4f22-8da9-e8bdbd82a35b

Image Courtesy of Science Facts

Take a look at this diagram. Don't worry too much about the variables, but F represents the force, q1 and q2 represent the magnitude of charges of the respective atoms, and r represents the distance between the nuclei of the atoms.

This image is basically showing you that is the foundation behind "opposites attract." is everywhere!

occurs if the charges are opposite (positive and negative), while occurs if the charges are the same (positive and positive or negative and negative).

Key Terms to Review (17)

Attraction

: In chemistry, attraction refers to the force that draws particles together due to opposite charges or polarities.

Bond Energy

: Bond energy is the amount of energy required to break a chemical bond and form neutral isolated atoms.

Bond Length

: Bond length is defined as the average distance between two bonded atoms in a molecule.

Bond Order

: Bond order is the number of chemical bonds between a pair of atoms. It indicates the stability of a bond.

Bond Strength

: Bond strength refers to the intensity or force with which atoms are held together in a molecule. It's directly related to bond length and inversely related to bond energy.

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.

Covalent Bonds

: A covalent bond is a type of chemical bond where two atoms share one or more pairs of electrons, resulting in a stable balance of attractive and repulsive forces.

Double Bond

: A double bond is a chemical linkage consisting of two shared electron pairs between two atoms.

Equilibrium Bond Length

: Equilibrium bond length is defined as the average distance between two bonded atoms where their potential energy is minimum (the most stable state).

Intermolecular Forces

: These are the forces that occur between molecules. They're weaker than intramolecular forces but still crucial for determining properties like boiling and melting points.

Internuclear Distance

: Internuclear distance is the distance between the nuclei of two atoms within a molecule.

Intramolecular Forces

: These are the forces that hold atoms together within a molecule. They are much stronger than intermolecular forces.

Ionic Bonds

: Ionic bonds are chemical bonds formed through the electrostatic attraction between oppositely charged ions (cations and anions).

Potential Energy

: Potential Energy refers to stored energy in an object due to its position or arrangement. In chemistry, molecules have potential energy based on their structure and composition.

Repulsion

: Repulsion in chemistry refers to the force that pushes particles apart when they have the same charge.

Single Bond

: A single bond is a type of chemical bond where two atoms share one pair of electrons.

Triple Bond

: A triple bond is a chemical linkage consisting three shared electron pairs between two atoms.

2.2 Intramolecular Force and Potential Energy

6 min readdecember 26, 2022

A

Anika P

Dalia Savy

Dalia Savy

A

Anika P

Dalia Savy

Dalia Savy

You may be thinking, what are ? are the forces between two atoms in a molecule! This is very different from intermolecular forces, which we learn in unit three.

💡 Intramolecular and are often confused, so here are some tips:

  • Intermolecular forces are those between molecules. Think inter = between two groups

  • Intramolecular forces are those between two groups in a molecule, so think intra = within a group.

So far, we learned about two intramolecular forces: and .

👉 For a review of what ionic bonds and covalent bonds are, as well as how to distinguish between the two, check out the linked study guide about the types of chemical bonds.

Potential Energy and Bonding

You may wonder where fits into bonding. Well, remember how chemistry favors and always strives to reach the highest stability? The lower the of a bond, the more stable it is! This is a fundamental rule you should try to keep in the back of your mind when learning about the strength and formation of bonds.

Because of this connection, physical or chemical processes can be described through energy diagrams. A graph of versus the distance between atoms is a useful tool for understanding the interactions between atoms. Taking a look at this graph, you can see several things:

  1. The "" - basically another phrase for the distance between atoms where is at its lowest point. Let's simplify it even more: the distance at which the atoms are the most stable.

  2. The - the amount of energy necessary to separate two atoms in a bond. This can be calculated or conceptually thought of as the difference in between the separated atoms and the atoms at their , or most stable phase.

  3. The strength of the bond - this can be grasped from the . In general, bonds with higher bond energies are stronger and more stable, while bonds with lower bond energies are weaker and less stable.

  4. The length of the bond, or the physical distance between the two atoms bonded to one another.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-2c55nRKO7lsX.png?alt=media&token=e065e03b-92f0-4887-a293-785cd65d3f9e

Image Courtesy of Stack Exchange

Potential Energy and Covalent Bonds

In molecular compounds with , the is influenced by both the size of the atoms and the .

is another term for how bonds can either be classified as single, double, or triple bonds.

Electrons Involved in Bond
(-)Two electronsLongestSmallest
(=)Four electronsMiddleMiddle
(≡)Six electrons ShortestLargest

An easy way to remember the number of electrons involved in a bond is that each dash on a lewis dot diagram corresponds to two shared electrons.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-POKnM2fBfVrB.gif?alt=media&token=54e6fe2e-bce5-4037-9f77-67fab496fbae

Image Courtesy of Shodor

Since bonds with higher bond energies are stronger and more stable, triple bonds are generally the most stable. This makes them the most difficult to break. However, it is important to note that stability also depends on other factors such as the size and charge of the atoms involved. Let's try and put some of this information together and take a look at a graph of .

Breaking Down a Potential Energy Diagram

For , the is influenced by the (single, double, triple) and the balance between repulsive and attractive forces. in the diagram shows how the greatest is the of two atoms. 

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-OMaXj4F3Hi3P.png?alt=media&token=5eadddef-db77-4cf7-ab1e-46eb90cd0341

Image Courtesy of SplainScience

Let's take a look at each of these stages:

  • - Since the atoms are very close together and the is very small, the atoms are experiencing lots of electron-electron . This causes the bond to be very unstable and leads to a of greater than zero.

  • Some overlap/ - This is the most stable state and the at this point is what we referred to as the "." There is a balance⚖️ between the repulsive and attractive forces and a stable bond is formed. Hopefully, now you understand why is lowest when the bond is stable.

    • The at this stage is the amount required to break the bond or the .

  • No overlap/ - Since the is so large, there are no interactions between the two atoms, and no bond is formed. This leads to a of almost zero.

Example with PE Diagrams

It is good to understand these properties because you may be asked to guess where an element falls on this graph.

Say the following image is a diagram of chlorine atoms bonded together (Cl-Cl). Where would Br-Br fall in comparison to chlorine's curve?

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-PvlVC0eJi3kI.png?alt=media&token=4fc580e8-9ba4-4054-83b0-0b24183fba7d

Image Courtesy of Chegg

To answer this question, we have to think about periodic trends and take a look at the axes of this graph:

  • : is the Cl-Cl bond or Br-Br bond longer? Well, the bond between the atoms with larger atomic radii would have to be the longer one. As you go down in a group on the periodic table, the atomic radius increases. Since bromine is below chlorine on the periodic table, the Br-Br bond is longer than the Cl-Cl bond.

    • This tells you where to draw the Br-Br curve in relation to the x-axis.

  • : which bond would be easier to break? Cl-Cl or Br-Br? This should automatically make you think of ionization energy. The lower the ionization energy, the easier it would be to break the bond. As you go down a group, ionization energy decreases because there are more occupied electron shells and the nucleus' with the valence electrons is weakest. Therefore, bromine has a lower ionization energy and the Br-Br bond is much easier to break.

    • This tells you where to draw the Br-Br curve in relation to the y-axis.

Knowing that the Br-Br bond is longer and easier to break, you would have to graph its curve up (less energy) and to the right more (larger ).

This question is a very good way to test your knowledge about this key topic and periodic trends. Here is what the graph should look like:

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-iOhbX69sGZzN.JPG?alt=media&token=62501919-d66b-4a6d-80fa-2a8014e22c17

Forces Within Ionic Bonds

Understanding the strength of ionic interactions involves the use of Coulomb's Law.

As we went over in the previous unit, you do not need to know the formula. However, you are expected to understand what conceptually means.

Essentially, the energy of two interacting charged particles (ions) depends on the magnitude of charge and the distance between the nuclei of the two particles.

  • The greater the charge of the atoms, the stronger the . This is because the more positively charged a nucleus is, the more strongly it can attract electrons toward it.

  • The closer the two particles are to each other, the stronger the . Think about it this way: magnets are not attracted to each other if they are placed 3 feet apart. They need to be close to feel the . 🧲

Smaller and highly charged ions have the strongest interactions, according to .

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-fTUXSu67u4ay.png?alt=media&token=9039b6ff-ee53-4f22-8da9-e8bdbd82a35b

Image Courtesy of Science Facts

Take a look at this diagram. Don't worry too much about the variables, but F represents the force, q1 and q2 represent the magnitude of charges of the respective atoms, and r represents the distance between the nuclei of the atoms.

This image is basically showing you that is the foundation behind "opposites attract." is everywhere!

occurs if the charges are opposite (positive and negative), while occurs if the charges are the same (positive and positive or negative and negative).

Key Terms to Review (17)

Attraction

: In chemistry, attraction refers to the force that draws particles together due to opposite charges or polarities.

Bond Energy

: Bond energy is the amount of energy required to break a chemical bond and form neutral isolated atoms.

Bond Length

: Bond length is defined as the average distance between two bonded atoms in a molecule.

Bond Order

: Bond order is the number of chemical bonds between a pair of atoms. It indicates the stability of a bond.

Bond Strength

: Bond strength refers to the intensity or force with which atoms are held together in a molecule. It's directly related to bond length and inversely related to bond energy.

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.

Covalent Bonds

: A covalent bond is a type of chemical bond where two atoms share one or more pairs of electrons, resulting in a stable balance of attractive and repulsive forces.

Double Bond

: A double bond is a chemical linkage consisting of two shared electron pairs between two atoms.

Equilibrium Bond Length

: Equilibrium bond length is defined as the average distance between two bonded atoms where their potential energy is minimum (the most stable state).

Intermolecular Forces

: These are the forces that occur between molecules. They're weaker than intramolecular forces but still crucial for determining properties like boiling and melting points.

Internuclear Distance

: Internuclear distance is the distance between the nuclei of two atoms within a molecule.

Intramolecular Forces

: These are the forces that hold atoms together within a molecule. They are much stronger than intermolecular forces.

Ionic Bonds

: Ionic bonds are chemical bonds formed through the electrostatic attraction between oppositely charged ions (cations and anions).

Potential Energy

: Potential Energy refers to stored energy in an object due to its position or arrangement. In chemistry, molecules have potential energy based on their structure and composition.

Repulsion

: Repulsion in chemistry refers to the force that pushes particles apart when they have the same charge.

Single Bond

: A single bond is a type of chemical bond where two atoms share one pair of electrons.

Triple Bond

: A triple bond is a chemical linkage consisting three shared electron pairs between two atoms.


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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.