Download CHAPTER-1 STRUCTURES AND PHYSICAL PROPERTIES ... and more Exams Chemistry in PDF only on Docsity! CHAPTER‐1 STRUCTURES AND PHYSICAL PROPERTIES Bond Polarity • Polarity in organic chemistry refers to a separation of charge and can describe a bond or an entire molecule. • A bond is said to be a polar bond,if it has partial positive charge at positive pole and partial negative charge at negative pole of two different atoms separated by a covalent bond. • Polarity of bond depends on electronegativity . • The ability of an atom to attract an electron towards itself is called as electronegativity. • If electronegativity is more than polarity is also more.for eg;F>O>Cl>N>Br>C>H. • so F has more electronegativity than other atoms. • The polarity of bond can lead to polarity of molecules, and thus profundly affect melting point and boiling point and solubility. Molecular Polarity • The polarity of the molecule is the sum of all of the bond polarities in the molecule. • A molecule is said to be a polar if the center of negative charge does noy coincide with the center of positive charge.such a moleculr consists of a DIPOLE. • DIPOLE means two equal and opposite charges separated in a space. • The molecule possess a dipole moment which is equal to the magnitude of the charge muitiplied by the distance between the centers of charge. • Water is a bent molecule with polar O‐H bonds. The bond dipole moments add to give a resultant dipole (m = 1.85 D) directed toward the more electronegative oxygen. • An Non¬‐ ionic compounds forms crystals in which the structural units are molecules. • for eg;Methane melts at the temperature of ‐1830C. BOILING POINT • The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. • A liquid in a vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high‐pressure has a higher boiling point than when that liquid is at atmospheric pressure. • In other words, the boiling point of a liquid varies depending upon the surrounding environmental pressure. For a given pressure, different liquids boil at different temperatures. • The normal boiling point (also called the atmospheric boiling point or the atmospheric pressure boiling point) of a liquid is the special case in which the vapor pressure of the liquid equals the defined atmospheric pressure at sea level, 1 atmosphere. At that temperature, the vapor pressure of the liquid becomes sufficient to overcome atmospheric pressure and allow bubbles of vapor to form inside the bulk of the liquid. • The standard boiling point is now defined by IUPAC as the temperature at which boiling occurs under a pressure of 1 bar. • Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation. • Evaporation is a surface phenomenon in which molecules located near the liquid's edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor.On the other hand, boiling is a process in which molecules anywhere in the liquid escape, resulting in the formation of vapor bubbles within the liquid. • Depending on the polar and non‐polar compounds also the boiling point varies.For eg; Non‐polar Methane boils at ‐ 161.50C and even polar Hydrogen chloride boils at only ‐850C. Acid & Base ACID: • A substance which when added to water produces hydrogen ions [H+]. BASE: • A substance which when added to water produces hydroxide ions [OH‐]. Bronsted‐Lowry Theory Bronsted‐Lowry Acid: • Any substance that acts as a proton donor is known as bronsted‐lowry acid • A Bronsted‐Lowry acid must have hydrogen somewhere in its formula. • When an electron is removed from a hydrogen atom... • A hydrogen ion is produced ‐ a proton. Bronsted‐Lowry Base: • Any substance that acts as a proton Acceptor is known as bronsted‐lowry base. • Most negative ions can acts as Bronsted‐Lowry bases. • The acid/base definitions are broadened because no specific ion must be formed,although hydrogen is the only source of protons. ISOMERISM: The existence of two or more compounds with same molecular formula but different properties is known as isomerism; and the compounds themselves are called isomers. The difference in properties of two isomers is due to the difference in the arrangement of atoms within their molecules. Isomerism may be of two types: • Structural isomerism. • Stereo isomerism. STRUCTURAL ISOMERISM: Chain (or) nuclear isomerism: This type of isomerism is due to the difference in the nature of the carbon chain (i.e. straight or branched) which forms the nucleus of the molecule e.g. (ii) Position isomerism: It is due to the difference in the position of the substituent atom or group or an unsaturated linkage in the same carbon chain. E.g. (iii) Functional isomerism: This type of isomerism is due to difference in the nature of functional group present in the isomers. E.g. (iv) Metamerism: It is due to the difference in nature of alkyl groups attached to the same functional group. This type of isomerism is shown by compounds of the same homologous series. E.g. . Stereo isomerism: When isomers have the same structural formula but differ in relative arrangement of atoms or groups in space within the molecule, these are known as stereoisomers and the phenomenon as stereoisomerism. Stereoisomerism is of two types • Geometrical isomerism • Optical isomerism Geometrical isomerism: