M.Mubeen MME M.Muneeb MME Zeeshan Rasool MME-17-12

ATOMIC BONDING

Primary Bonds: Primary Bond is a bond which is formed by sharing of electrons between two atoms or by transfer of electrons from one atom to other. Types: 1. Metallic Bond 2. Covalent Bond 3. Ionic Bond

Metallic Bond: “The Metallic Bond forms when atoms give up their valence electron, then form an electron sea.” The Metal cations and electrons are oppositely charged and are attracted to each other. When voltage is applied, the sea of electron can move freely to produce a current. Properties:  High Melting & Boiling Point  Conduct Electricity & Heat  Hard & Dense  Malleable & Ductile

Covalent Bond: Covalent Bonds are formed by Sharing of Valance electron among two or more atoms. Covalent Bonds Are Directional. In silicon, a tetrahedral structure is formed, with angles of ◦ required between each covalent bond Properties:  Hard & Brittle  High Melting Point  Poor Conductivity ( Semiconductors )  Limited Ductility ( Due To Directional Relationship ) e.g. Conductive Polymers, Silica, Dimond

Ionic Bonds The Ionic Bonds are formed between two different atoms when one atom donates its valance electrons to the second atom. An electrostatic attraction binds the ions together. Cation: The atom that donates its valance with a positive charge is called a cation. Anion: The atom that accepts the electrons acquires a net negative charge is called Anion. Properties:  soft  Low Melting Points  Nonconductors e.g. NaCl (Table Salt)

Secondary Bonds A Secondary Bond on the other hand is the one where no true sharing of electrons or transfer does occur. Examples of secondary bonding are Hydrogen Bonding, Dipole-dipole Interaction, Van der waal`s forces e.t.c. Secondary bonds are weak in comparison to primary bonds.

Van der waals Bond A Secondary Bond Developed between atoms and molecules as a result of interactions between dipoles that are induced or permanent. Properties:  They are weaker than normal covalent ionic bonds with a strength of 0.2eV/atom.  Van der waals bonds occur between neutral atoms and molecules.  They have no directional characteristics.  Van der waals forces are independent of temperature except dipole-dipole interactions.