grade 12 week 2.pptx

grade 12 week 2.pptx

• 1.
  Types of Intermolecular Forces- London Dispersion,Dipole– Dipole, Hydrogen Bonding
• 2.
  The properties of liquidsare intermediate between those of gases and solids, but are more similar to solids.
• 3.
  Intermolecular forces determinebulk properties, such as the melting points of solids and the boiling points of liquids. Liquids boil when the molecules have enough thermal energy to overcome the intermolecular attractive forces that hold them together, thereby forming bubbles of vapor within the liquid. Similarly, solids melt when the molecules acquire enough thermal energy to overcome the intermolecular forces that lock them into place in the solid.
• 4.
  Intermolecular forces areelectrostatic in nature; that is, they arise from the interaction between positively and negatively charged species. Like covalent and ionic bonds, intermolecular interactions are the sum of both attractive and repulsive components. Because electrostatic interactions fall off rapidly with increasing distance between molecules, intermolecular interactions are most important for solids and liquids, where the molecules are close together. These interactions become important for gases only at very high pressures, where they are
• 5.
  1. Dipole-Dipole Interaction Dipole-dipoleinteraction exists between the differently charged particles of a molecule. In other words, the interconnection that lies within a part of a molecule that is partially negatively charged and another part of a molecule that is partially positively charged is called a dipole-dipole interaction. The only requirement of such interaction force to exist is that the elements must be charged with different polarity charges. These are the strongest intermolecular forces of attraction existing in nature. For example, a dipole-dipole force of attraction helps to bind a hydrogen atom with a chlorine atom to form a
• 7.
  2. Hydrogen Bonding Hydrogenbonding is a special case of dipole-dipole interaction. It specifically occurs when a hydrogen atom is bonded to a nitrogen, oxygen, or fluorine atom. Hydrogen consists of a partially positive charge, whereas oxygen, fluorine, or nitrogen are partially negatively charged. This difference in the polarity of charges on the atoms establishes a force of attraction, which is responsible for a hydrogen bond to exist between them. It is highly difficult to break hydrogen bonds and therefore requires a lot of energy. Some examples of a hydrogen bond are water (H2​O) and hydrogen fluoride (HF). This is the reason why the
• 9.
  3. London DispersionForces London dispersion forces occur between temporary or induced dipoles. It is a temporary force of attraction that exists between the electrons of two adjacent atoms. These are the weakest of all the intermolecular forces. London dispersion force is proportional to the number of electrons contained by a molecule. They are a part of van der Waals forces. The more be the London dispersion force, the more will be the boiling point of the compound. These forces do not require a huge amount of
• 11.
  VAN DER WAALS FORCES: Vander waals forces are the weak forces that contribute to the intermolecular bonding between molecules. Molecules inherently possess energy and their electrons are always in motion, so transient concentration of electrons in one region Of a molecule to be attracted to the electrons of another molecule. Similarly, negatively charged regions of another
• 12.
  KEY TAKE AWAYS:VAN DER WAALS FORCES • Van der Waals forces are distance- dependent forces between atoms and molecules not associated with covalent or ionic chemical bonds • Sometimes the term is used to encompass all intermolecular forces, although some scientists only include among them the London dispersion force. • Van der Waals forces are the weakest of
• 13.
  PROPERTIES OF VANDER WAALS FORCES • They are additive • They are weaker than either ionic or covalent chemical bonds. • They are not directional • They act only over a short range. The interaction is greater when molecules draw closer. • They are independent of temperature, with the exception of dipole-dipole interactions.
• 14.
  4 MAJOR CONTRIBUTIONSOF VAN DER WAALS FORCE 1.A negative component prevents molecules from collapsing. This is due to Pauli exclusion principle 2.Either an attractive or a repulsive electrostatic interaction occurs between permanent charges. 3.Induction or polarization occurs. This is the attractive forces between permanent polarity on one molecule and an induced polarity on another. 4.London dispersion forcer is the attraction between any pair of molecules due to instantaneous polarization.
• 15.
  Examples: 1. DNA Deoxyribonucleic Acidor DNA is a chemical compound that stores all the genetic information of a living being. Hydrogen bonding is responsible for the existence of a DNA molecule. A strong force of interaction existing between the four parts, namely
• 16.
  2. Proteins Proteins arelong chain polymers made up of amino acids. These long chains are known as polypeptides. They play a key role in the life of all living beings. The primary structure of proteins is formed by the covalent bond existing between the amino acid molecules. The secondary structure is made up of the hydrogen bonding present between the different sections of the protein chain. The process with which a protein compound folds and forms its tertiary
• 17.
  3. Plants The movementof water through the xylem and other parts of a plant makes use of hydrogen bonding. Plants containing tiny and rigid tubes that are made up of cellulose. A strong adhesive force exists between water and the cellulose walls. This force supports the capillary action that is used to supply nutrients and fluids to the stem, trunk, and other parts of a plant. Hydrogen bonding is responsible for the upward
• 18.
  4. Soap andDetergents The soap bubbles are made up of soap molecules and water molecules. Water is a polar molecule, whereas a soap bubble has a polar and non- polar end. The polar ends of both the molecules get attracted to each other, which helps in the establishment of an intermolecular force. This intermolecular interaction is
• 19.
  5. Water Water iscomposed of hydrogen and oxygen atoms. The atoms are bonded to each other using the hydrogen bond. A hydrogen bond is a special form of the dipole-dipole bond that exists between partially positive hydrogen and partially negative oxygen of another molecule. The intermolecular force existing within the compounds helps the water molecules to stick to each other. The hydrogen bond is the strongest intermolecular bond, which is why it is difficult to