Reason for glass rod losing electrons

[vcsharp2003]

Homework Statement

When a glass rod is rubbed with silk cloth then it becomes positively charged, while the silk cloth becomes negatively charged. Why does glass rod lose electrons to silk cloth?

Relevant Equations

None

I am not sure if the explanation below is enough. This is a high school level question.

When rubbing occurs between glass and silk, then heat energy is produced which provides the energy needed to free up electrons in outermost orbits of atoms in silk or glass. But silk has very tightly bound electrons in outermost orbit which prevents the electrons from freeing up, whereas glass has less tightly bound electrons in outermost orbit and the energy is sufficient to free the electrons in outermost orbit.

 

[anuttarasammyak]

Say two charge neutral materials touch, one could become positive charged with other negative due to energy level difference of electrons. The two keep charged after separation. I hope this is a rough sketch of the phenomena.

 

[vcsharp2003]

Say two charge neutral materials touch, one could become positive charged with other negative due to energy level difference of electrons. The two keep charged after separation. I hope this is a rough sketch of the phenomena.

What is energy level of an electron in an atom? Is it the electrical potential energy of an electron?

 

[Drakkith]

When rubbing occurs between glass and silk, then heat energy is produced which provides the energy needed to free up electrons in outermost orbits of atoms in silk or glass.

While this might happen to some degree, I think the main cause is the difference in electrochemical potential between the two different materials.

 

[vcsharp2003]

While this might happen to some degree, I think the main cause is the difference in electrochemical potential between the two different materials.

You mean the silk cloth has a higher electric potential than glass rod?

 

[Drakkith]

You mean the silk cloth has a higher electric potential than glass rod?

Per wiki: https://en.wikipedia.org/wiki/Triboelectric_effect

Although the part 'tribo-' comes from the Greek for "rubbing", τρίβω (τριβή: friction), the two materials only need to come into contact for electrons to be exchanged. After coming into contact, a chemical bond is formed between parts of the two surfaces, called adhesion, and charges move from one material to the other to equalize their electrochemical potential. This is what creates the net charge imbalance between the objects. When separated, some of the bonded atoms have a tendency to keep extra electrons, and some a tendency to give them away, though the imbalance will be partially destroyed by tunneling or electrical breakdown (usually corona discharge). In addition, some materials may exchange ions of differing mobility, or exchange charged fragments of larger molecules.

Unfortunately I don't know enough about this topic to discuss it in more detail.

Edit: Just realized this was in the homework section, else I wouldn't have answered since I don't know too much about this phenomenon.

 

[vcsharp2003]

and charges move from one material to the other to equalize their electrochemical potential

It seems that electrons are unstable in outermost orbit if that orbit is not fully occupied and will therefore be in a higher energy state i.e higher electrochemical potential. If outermost orbit is fully occupied then electrons are in a stable state and have a lower electrochemical potential.

From what I remember, the number of electrons in an orbit is $2n^2$ where n can be 1,2,3,4 or any postive integer.

 

[Steve4Physics]

Homework Statement:: When a glass rod is rubbed with silk cloth then it becomes positively charged, while the silk cloth becomes negatively charged. Why does glass rod lose electrons to silk cloth?
Relevant Equations:: None

I am not sure if the explanation below is enough. This is a high school level question.

When rubbing occurs between glass and silk, then heat energy is produced which provides the energy needed to free up electrons in outermost orbits of atoms in silk or glass. But silk has very tightly bound electrons in outermost orbit which prevents the electrons from freeing up, whereas glass has less tightly bound electrons in outermost orbit and the energy is sufficient to free the electrons in outermost orbit.

I think the above explanation is incorrect because:
1) 'heat energy' is not responsible for the electron transfer;
2) the process is more complex than can be explained by simply considering individual atoms and their electrons. (Also, silk is a complex polymer containing several diffferent types of atom.)

This is a rather unfair question unless you have actually studied triboelectricity.

For high school level I would just say something like this:
The silk has a larger affinity for electrons than does the glass. Rubbing enables some outer atomic electrons to be transferred. Therefore there is a net transfer of electrons from the glass to the silk. This leaves the glass positive (overall more protons than electrons) and the silk negative (overall more electrons than protons).

Out of interest, note that the correct term for the production of charge through friction/contact is the triboelectric effect. Different materials have different affinities (affinity = liking) for electrons and this gives rise to a triboelectric series for a given set of different materials e.g.
https://engineerblogs.org/wp-content/uploads/2011/04/quiz_tribolelectric.jpeg

And Wikipedia says this:
“After coming into contact, a chemical bond is formed between parts of the two surfaces, called adhesion, and charges move from one material to the other to equalize their electrochemical potential. This is what creates the net charge imbalance between the objects. When separated, some of the bonded atoms have a tendency to keep extra electrons, and some a tendency to give them away, though the imbalance will be partially destroyed by tunneling or electrical breakdown (usually corona discharge). In addition, some materials may exchange ions of differing mobility, or exchange charged fragments of larger molecules“
https://en.wikipedia.org/wiki/Triboelectric_effect

Also, do not confuse electrochemical potential with electric potential. They are not the same thing.

 

[vcsharp2003]

This is a rather unfair question unless you have actually studied triboelectricity.

Thankyou for a detailed explanation.

Triboelectricity is new to me and not even in our textbook.