Bonds In Solids, Isotopy and AnIsotropy.pptx

Bonds: These are positive interactions between particles represent bonds. A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds.
The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds.
In nanotechnology, bonds play a fundamental role in determining the structure, properties and functionality of nanomaterials.

1. Bonds In Solids, An Isotropy Submitted to: Dr. Lav Bhushan Submitted by: Shivalika Ph.D. 1 st year (A-2023-40-010) Course Title: Introduction to Nanotechnology Course code: Soils 514 Department of Agronomy, CSK HPKV, Palampur, 176062

2. CONTENT Introduction Classification of solids Types of bond Isotropy and anisotropy Anisotropy in nano -materials and its application Conclusion

3. Introduction Bonds: These are positive interactions between particles represent bonds. A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the electrostatic force between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds. In nanotechnology, bonds play a fundamental role in determining the structure, properties and functionality of nanomaterials .

4. Classification of solids Solids can be classified according to the nature of the bonding between their atomic or molecular components. The traditional classification distinguishes four kinds of bonding: Covalent bonding : forms network covalent solids (sometimes called simply "covalent solids") Ionic bonding: forms ionic solids Metallic bonding: forms metallic solids Weak inter molecular bonding: forms molecular solids (sometimes anomalously called "covalent solids")

5. Ionic Bonds These occur between positively and negatively charged ions. They are typically found in salts, such as sodium chloride ( NaCl ). Ionic bonds are strong and contribute to the high melting points and brittleness of ionic solids . It is the simplest type of interatomic bond. In nanotechnology, ionic bonds play a significant role in the synthesis, assembly and properties of nanomaterials .

6. Properties of ionic bond The ionic bonds are the strongest of all the bonds. The ionic bond has charge separation , and so they are the most reactive of all the bonds in the proper medium. They have high melting and boiling point . They are good conductors of electricity in aqueous solutions. In Nanotechnology: Synthesis of nanoparticles : Many nanoparticles are synthesized through chemical reactions involving ionic compounds. Ionic bond contribute to the stabilization of nanomaterials in solution or in solid state matrices. Ionic interactions can be exploited to design controlled release systems for drug delivery in nanomedicines . Nanomaterials with ionic bonds can be employed in environmental remediation and catalysis.

7. Covalent Bonds Covalent bonds involve the sharing of electron pairs between atoms, resulting in the formation of stable molecular structures.   such bonds are mainly found in organic molecules and in non-electrolytes. E.g. Chlorine, fluorine, methane, etc. In the formation of this bond between two atoms and the each atom contributes electron in equal number. Contributed electrons are shared by both the atoms.

8. Properties of covalent bond Covalent bonds are weaker than ionic or metallic bonds. Low melting and boiling point Poor conductor of electricity Soft and flexible Nonpolar covalent compounds dissolve poorly in water. Small covalent compounds tends to be gases, with relatively weak intermolecular forces

9. Comparison between ionic and covalent bond Characteristics Ionic bond Covalent bond Description It is formed between a metal and a no metal. Non metals are stronger than the metal and can get electrons very easily from the metal. These two opposite ions attract eachother and form ionic bond. It is formed between two non metals that have similar electronegativities . Neither atom is strong enough to attract electrons from the other. For stabilization, the share their electrons from outer molecular orbit with others. Shape No definite Definite Polarity High Low Melting point High Low Boiling point High Low State at room temperature Solid Liquid or gaseous Examples Methane, Hydrochloric acid Sodium chloride, Sulphuric acid

10. Metallic Bonds These bonds involve a “sea” of delocalized electrons around a lattice of metal cations . This bonding type is responsible for properties such as electrical conductivity, malleability, and ductility in metals like sodium, copper and aluminum . The factors that affect the strength of a metallic bond include: Total number of delocalized electrons. Magnitude of positive charge held by the metal cation . Ionic radius of the cation Metallic bonds are not broken when the metal is heated into the melt state. Instead, these bonds are weakened, causing the metal ions to lose their definite, rigid structure and become liquid. However, these bonds are completely broken when the metal is heated to its boiling point.

11. Comparison between ionic and metallic bond Characteristics Ionic bond Covalent bond Binding force The bond exist due to electrostatic force of attraction between possitive and negative ions The bond exist due to force of attraction between the electron cloud of valence electrons and positive ions of the same or different. Bond formation Ionic bonds are most easily formed whenone of the atoms has smaller number of valence electrons, such as the alkali metals and alkaline earths. This type of bond is charateristics of metallic elements. The elements having smaller number of valence electrons, which are loosely held, so that they can be released to the common pool. Conductivity Low Good Strength Stronger than metallic Less stronger than ionic

12. Van der Waals Forces These are weak, non-covalent interactions that include dipole-dipole interactions and London dispersion forces. They are significant in molecular solids and contribute to the properties of materials like graphite and many organic compounds . Vander Waals is important in nanotechnology, because the building units are usually solids and consist of molecules instead of individual atoms.

13. Hydrogen Bonds A special type of dipole-dipole interaction, these occur when hydrogen is bonded to a highly electronegative atom like oxygen or nitrogen. They are weaker than ionic and covalent bonds but crucial in biological molecules and many polymers.

14. Co-ordinate bond Co-ordinate bond is a type of alternate covalent bond that is formed by sharing of electron pair from a single atom . Both shared electrons are donated by the same atom. It is also called dative bond or dipolar bond. Co-ordinate covalent bonds are usually formed in reactions that involve two non-metals such as a hydrogen atom or during bond formation between metals ions and ligands .

15. In this type of bonding, the atom that shares an electron pair from itself is termed as the donor. The other atom which accepts these shared pair of electrons is known as a receptor or acceptor . The bond is represented with an arrow →, pointing from the donor to acceptor atom . After sharing of electron pair each atom gets stability. Co-ordinate bond These have lower melting and boiling points than ionic compounds. Some of these compounds exhibit isomerism . Sharing of electrons takes place in a definite direction , hence, it is a directional bond. It is weaker than ionic bonding.

16. Isotropy and Anisotropy in Nanotechnology Isotropic Materials: These materials have properties that are identical in all directions. For example, glass and metals are often isotropic at the macroscopic scale. Isotropic materials are easier to work with in many applications because their uniform properties simplify design and manufacturing processes. Anisotropic Materials: These materials have direction-dependent properties. Examples: include crystals, composites , and certain engineered nanomaterials . Anisotropy can be leveraged to achieve specific mechanical, optical, or electronic properties that are advantageous in various applications .

17. Anisotropy in nano -materials Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. • Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nano -particles brings novel properties into the resulting system, which would be entirely different from the properties of individual nano -particles.

18. Application of anisotropy in Nanotechnology 1. Enhanced Mechanical Properties Anisotropic nano -materials, such as carbon nanotubes (CNTs) and graphene , exhibit exceptional mechanical properties along certain directions. For instance, CNTs have extremely high tensile strength and stiffness along their longitudinal axis, making them ideal for reinforcing composite materials used in aerospace, automotive, and construction industries. 2. Improved Thermal Conductivity Materials like graphene and boron nitride nanosheets exhibit high thermal conductivity along specific directions. This anisotropy in thermal properties can be exploited in thermal management applications, such as in electronic devices where efficient heat dissipation is crucial. 3. Superior Electrical Conductivity Anisotropic nano -materials can show enhanced electrical conductivity in certain directions. For example, graphene exhibits excellent electrical conductivity along its plane, making it suitable for use in flexible electronics, conductive films, and advanced batteries.

19. 4. Optoelectronic Devices Anisotropic materials like black phosphorus and transition metal dichalcogenides (TMDs) have direction-dependent optical and electronic properties. These materials are being investigated for use in next-generation optoelectronic devices, including photodetectors , light-emitting diodes (LEDs), and solar cells. 5. Magnetic Applications Anisotropic magnetic nano -materials, such as cobalt nanowires and iron oxide nanoparticles , show direction-dependent magnetic properties. These materials are used in data storage devices, magnetic sensors, and biomedical applications, including targeted drug delivery and magnetic resonance imaging (MRI) contrast agents. 6. Anisotropic Catalysis Anisotropic nano -materials can exhibit enhanced catalytic properties along specific crystallographic directions or facets. This is crucial in catalytic reactions where certain facets of a nanoparticle are more active. For example, anisotropic gold nanoparticles can catalyze reactions more efficiently due to their high surface area and specific active sites. 7. Sensing Applications The anisotropic properties of nano -materials can be used to develop highly sensitive sensors. For example, anisotropic conductive polymers can change their electrical resistance significantly when stretched or compressed in specific directions, making them suitable for strain sensors and flexible electronic applications.

20. 8. Directed Self-Assembly Anisotropic interactions can guide the self-assembly of nano -materials into well-defined structures, which are important for creating complex nano -architectures in materials science and nanotechnology. These self-assembled structures can have unique properties not present in the individual components. 9. Biomedical Applications Anisotropic nanoparticles can be designed for targeted drug delivery, where their shape and surface properties influence their interaction with biological tissues and cells. For example, rod-shaped nanoparticles can penetrate cellular membranes more effectively than spherical ones, enhancing drug delivery efficiency. 10. Photonic Crystals Anisotropic nano -materials can be used to create photonic crystals that control the flow of light in various directions. These materials can be used in developing advanced optical devices, including waveguides, lasers, and optical fibers , where control over light propagation is crucial. 11. Quantum Computing Anisotropic materials like topological insulators and certain 2D materials exhibit unique electronic properties that are direction-dependent. These materials are being explored for their potential use in quantum computing, where control over quantum states and electron paths is essential.

21. Conclusion In the context of nanotechnology, the type of bonding in nanoscale solids—ionic, covalent, metallic, van der Waals, or hydrogen—crucially affects their physical properties, such as melting point, hardness, and conductivity. Isotropic nanomaterials , with uniform properties in all directions, are useful for applications requiring consistent performance. Anisotropic nanomaterials , like carbon nanotubes and graphene , exhibit direction-dependent properties due to their unique atomic structures, leading to exceptional electrical and thermal conductivity and mechanical strength in specific directions. Understanding these bonding types and anisotropy at the nanoscale is vital for designing advanced nanodevices and materials for cutting-edge applications in electronics, photonics, and biomedical engineering.