(a) What is a dielectric?
A dielectric is an insulating material that can be polarized by an applied electric field. When a dielectric is placed in an electric field, it does not conduct electricity but instead undergoes a shift in charge distribution, leading to the alignment of its molecular dipoles. This alignment reduces the overall electric field within the material. Dielectrics are used in various applications, including capacitors, where they increase the capacitance by reducing the effective electric field and thereby allowing more charge to be stored for a given voltage.
(b) What are polar and non-polar molecules?
Polar Molecules
Polar molecules have a permanent electric dipole moment due to the uneven distribution of electrons between atoms with different electronegativities. This results in partial positive and negative charges within the molecule.
Examples:
- Water (H₂O): Oxygen is more electronegative than hydrogen, creating a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.
- Ammonia (NH₃): Nitrogen is more electronegative than hydrogen, leading to a dipole moment where the nitrogen has a partial negative charge and the hydrogen atoms have partial positive charges.
Non-Polar Molecules
Non-polar molecules either have an even distribution of electrons or their dipole moments cancel out due to symmetric arrangements. These molecules do not have permanent dipole moments.
Examples:
- Methane (CH₄): The molecule has a symmetric tetrahedral structure with equal distribution of electrons, resulting in no net dipole moment.
- Carbon Dioxide (CO₂): Although the C=O bonds are polar, the linear geometry causes the dipole moments to cancel each other out, resulting in a non-polar molecule.
(c) Define Atomic Polarizability
Atomic polarizability refers to the ability of an atom to be distorted by an external electric field, leading to the formation of an induced dipole moment. When an electric field is applied, the electron cloud around the nucleus can be displaced relative to the nucleus, creating a temporary dipole. The extent of this displacement is characterized by the polarizability, which depends on the electron cloud's size and the binding strength of the electrons to the nucleus.
Atomic polarizability plays a crucial role in various phenomena, such as the dielectric behavior of materials, van der Waals forces, and the refractive index of substances.
