Electro Negativity And Chemical Bonding L-1 & 2 PDF

Electronegativity and chemical bonding Dr. Adil Farooq Wali Associate Professor Faculty of Pharmaceutical Chemistry RAKMHSU L1&2 RAK College of Pharmacy  Learning Outcomes At the end of this lecture, the students will be...

Electronegativity and chemical bonding Dr. Adil Farooq Wali Associate Professor Faculty of Pharmaceutical Chemistry RAKMHSU L1&2 RAK College of Pharmacy  Learning Outcomes At the end of this lecture, the students will be able to Differentiate between ionic and covalent bonding Classify the bonding in a compound as ionic or covalent. RAK College of Pharmacy  Course Content ❖ Introduction ❖ Types of bonds ❖ Intermolecular forces RAK College of Pharmacy  Introduction Chemical Bonding refers to the formation of a chemical bond between two or more atoms, molecules, or ions to give rise to a chemical compound. These chemical bonds are what keep the atoms together in the resulting compound. RAK College of Pharmacy  Introduction A chemical bond is an attraction between atoms that enables the formation of an element (N2) or compound (NaCl). RAK College of Pharmacy  Introduction RAK College of Pharmacy  Introduction The attractive force which holds various constituents (atom, ions, etc.) together and stabilizes them by the overall loss of energy is known as chemical bonding. Therefore, it can be understood that chemical compounds are dependent on the strength of the chemical bonds between their constituents; The stronger the bonding between the constituents, the more stable the resulting compound would be. RAK College of Pharmacy  Introduction The opposite also holds true; if the chemical bonding between the constituents is weak, the resulting compound would lack stability and would easily undergo another reaction to give a more stable chemical compound (containing stronger bonds). To find stability, the atoms try to lose their energy. RAK College of Pharmacy  Introduction Whenever matter interacts with another form of matter, a force is exerted on one by the other. When the forces are attractive in nature, the energy decreases. When the forces are repulsive in nature, the energy increases. The attractive force that binds two atoms together is known as the chemical bond. RAK College of Pharmacy  Types of Chemical Bonds When substances participate in chemical bonding and yield compounds, the stability of the resulting compound can be measured by the type of chemical bonds it contains. The type of chemical bonds formed vary in strength and properties. There are 4 primary types of chemical bonds which are formed by atoms or molecules to yield compounds. RAK College of Pharmacy  Types of Chemical Bonds These types of chemical bonds include: ✓ Ionic Bonds ✓ Covalent Bonds ✓ Hydrogen Bonds ✓ Polar Bonds These types of bonds in chemical bonding are formed from the loss, gain, or sharing of electrons between two atoms/molecules. RAK College of Pharmacy  Ionic Bonding Ionic bonding is a type of chemical bonding which involves a transfer of electrons from one atom or molecule to another. Here, an atom loses an electron which is in turn gained by another atom. When such an electron transfer takes place, one of the atoms develops a negative charge and is now called the anion. RAK College of Pharmacy  Ionic Bonding The other atom develops a positive charge and is called the cation. The ionic bond gains strength from the difference in charge between the two atoms, i.e. the greater the charge disparity between the cation and the anion, the stronger the ionic bond. RAK College of Pharmacy  Ionic Bonding Example: NaF (Sodium fluoride) Sodium and fluorine undergo a redox reaction to form sodium fluoride. Sodium loses its outer electron to give it a stable electron configuration, and this electron enters the fluorine atom exothermically. The oppositely charged ions are then attracted to each other to form a solid. RAK College of Pharmacy  Covalent Bonding A covalent bond indicates the sharing of electrons between atoms. Compounds that contain carbon (also called organic compounds) commonly exhibit this type of chemical bonding. The pair of electrons which are shared by the two atoms now extend around the nuclei of atoms, leading to the creation of a molecule. RAK College of Pharmacy  Covalent Bonding Example: H2 (Hydrogen gas) A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. The given animation shows how hydrogen atoms form H2 while sharing two electrons. RAK College of Pharmacy  Polar Covalent Bonding Covalent bonds can be either Polar or Non-Polar in nature. In Polar Covalent chemical bonding, electrons are shared unequally since the more electronegative atom pulls the electron pair closer to itself and away from the less electronegative atom. Water is an example of such a polar molecule. RAK College of Pharmacy Polar Covalent Bonding RAK College of Pharmacy  Polar Covalent Bonding A difference in charge arises in different areas of the atom due to the uneven spacing of the electrons between the atoms. One end of the molecule tends to be partially positively charged and the other end tends to be partially negatively charged. RAK College of Pharmacy  Hydrogen Bonding Compared to ionic and covalent bonding, Hydrogen bonding is a weaker form of chemical bonding. It is a type of polar covalent bonding between oxygen and hydrogen wherein the hydrogen develops a partial positive charge. This implies that the electrons are pulled closer to the more electronegative oxygen atom. RAK College of Pharmacy  Hydrogen Bonding This creates a tendency for the hydrogen to be attracted toward the negative charges of any neighboring atom. When a hydrogen atom serves as a bridge/link between two highly electronegative atoms like F, O & N, holding one by a covalent bond and the other by purely electrostatic forces is called hydrogen bonding. RAK College of Pharmacy  Hydrogen Bonding Examples: Water (H2O) The positive charge on hydrogen in a molecule of water will be attracted electrostatically by the negative charge of the oxygen atom in another molecule of water. RAK College of Pharmacy  Hydrogen Bonding Types of hydrogen bonding: Intermolecular hydrogen bonding: When hydrogen bonds are formed between two or more molecules of the same or different compounds they are called intermolecular hydrogen bonding. Example: p-Nitrophenol RAK College of Pharmacy  Hydrogen Bonding Intramolecular hydrogen bonding: When hydrogen bonds are formed between the atoms of the same molecules they are called Intramolecular hydrogen bonding. Example: o-Nitrophenol RAK College of Pharmacy  Hydrogen Bonding Importance of hydrogen bond: It explains the physical properties of the molecule like melting and boiling point, solubility in water, and spectral characteristics. Hydrogen bonds in polypeptide chains in proteins play an important role in determining the precise structure and shape of the proteins. The concept of hydrogen bonds can explain diverse phenomena such as chemotherapeutic action of drugs etc. RAK College of Pharmacy References and suggested Books RAK College of Pharmacy THANKS RAK College of Pharmacy