Charge Transfer and its Methods

What is Charge Transfer Complex?

A charge transfer complex also called as the electron donor acceptor complex can be defined as an association of two or more molecules, or of different parts of a large molecule, in which a fraction of electronic charge is transferred between the molecular entities. Charge transfer often occurs in inorganic ligand chemistry involving metals.

We all have observed that when we charge a piece of plastic, a comb or a pen and position it near small pieces of paper they get attracted towards it. We also observe that; the comb loses its charge after a few moments. Can we guess why this happens? Where does the charge go? We can say the charge gets transferred to our hand and eventually to the ground. But how does this phenomenon occur? In this section, we shall learn about the phenomenon of charge transfer and the methods by which it occurs.

Methods of Charge Transfer

There are two methods through which charge transfer can take place between two bodies.

  • Charging by Conduction
  • Charging by Induction

Charge transfer by Conduction

The charge transfer by conduction process involves touching of a charged particle to a conductive material. This way the charges are transferred from the charged material to the conductor. This method is useful for charging conductors.

Charge transfer by conduction using a negatively charged object

As we know like charges repel each other and spread about as far as possible in order to reduce this repulsion. In doing so, the electrons (negatively charged) go to the extreme of the perimeter of the sphere and if there is a pathway to another object where the electrons can go, the electrons tend to move from one object to another. Let us consider a negatively charged metal sphere as shown in the figure.

When the charged metal sphere comes in contact with a neutral object, excess electrons from the sphere move onto the neutral object and gets spread evenly. As a result of this process, the object 2 acquires negative charge while the metal sphere is still charged but has less number of electrons. This process of charging by contact is termed as charging by conduction.

Charge transfer by conduction using a negatively charged object

Charge transfer by conduction using a positively charged object

As we know, a positively charged sphere has an excess of protons which in other terms means a deficit of electrons. Let us consider two objects one positively charged metal plate and a neutral metal sphere. When a positively charged metal plate comes in contact with a neutral metal sphere, the electrons from the neutral sphere get attracted towards the positively charged metal plate. This process lasts until the positive charge in the metal plate becomes redistributed. Having lost electrons to the positively charged plate, the neutral sphere experiences a deficit of electrons which makes it positively charged while the positively charged metal plate is still charged but the deficit of electron is comparatively less than before. This process of charge transfer is defined as the charge transfer using a positively charged object.

Charge transfer by conduction using a positively charged object

In the above example, we learnt about charge transfer through the process of conduction using a positive or a negatively charged object. Charge transfer can also take place through the process of induction.

Charge transfer by Induction

Induced-charge separation is a shift in the position of electrons in a neutral object that occurs when a charged object is brought near it whereas charging by induction is the charging of a neutral object by bringing another charged object close to; but not touching, the neutral object.

Charging more than one object by induction a positively charged object can be used to induce a charge in a neutral object. You can also use two objects at the same time to permanently charge the objects. In sphere A, the electrons are attracted by the positive charge on the balloon. The electrons the balloon draw electrons in sphere A to the left side. The right side of the sphere becomes negatively charged. Electrons in sphere B are attracted to sphere A and are transferred. Keep the balloon in place and remove sphere B from sphere A, makes sphere B permanently charged positively. Electrons are unable to move back. Remove the balloon form sphere A allows the electrons to spread throughout the sphere, yet it is still negatively charged.

Charge transfer by induction using a positively charged object

Taking two spheres A and B, touching each other, as shown in the figure, if we bring a positively charged balloon near sphere A, the electrons from sphere B migrate towards sphere A due to the attraction between opposite charges, thus leaving the sphere B deficit of electrons. As a result, the sphere A gets negatively charges and sphere B gets positively charged. The spheres are then separated using an insulating cover, a stand or gloves. When the balloon is removed, the charges in sphere A and B redistribute, spreading out evenly.