Chemical Bonds PDF

Created by Turbolearn AI Chemical Bonds Chemical bonds have a significant effect on the chemical and physical properties of compounds. They involve the valence electrons, which are the electrons in the outermost energy level of an atom. Valence Electrons The valence electrons are the electrons tha...

Created by Turbolearn AI Chemical Bonds Chemical bonds have a significant effect on the chemical and physical properties of compounds. They involve the valence electrons, which are the electrons in the outermost energy level of an atom. Valence Electrons The valence electrons are the electrons that participate in bond formation and are also known as bonding electrons. The number of valence electrons in an atom can be determined by its position in the periodic table. For example: Element Number of Valence Electrons Hydrogen H 1 Oxygen O 6 Aluminum Al 3 Nitrogen N 5 Lewis Structure A Lewis structure, also known as an electron dot diagram, is a way of drawing the outer energy level electrons valence of an atom. It consists of an element's symbol surrounded by dots to represent the number of valence electrons. A Lewis symbol of an element consists of an element's symbol and surrounding dots to represent the number of valence electrons. Electronic Theory of Valence The electronic theory of valence states that atoms interact by losing, gaining, or sharing electrons to reach a stable noble gas configuration. This theory was developed by G.N. Lewis and W. Kossel in 1916. In chemical bond formation, atoms interact by losing, gaining, or sharing of electrons so as to reach a stable noble gas configuration. Page 1  Created by Turbolearn AI Octet Rule The octet rule, also known as the rule of eight, states that atoms interact by electron-transfer or electron-sharing to achieve a stable outer shell of eight electrons. Atoms with less than 4 electrons tend to lose electrons. Atoms with more than 4 electrons tend to gain electrons. There are some exceptions to this rule. Oxidation Number The oxidation number is the charge that an atom would have if it lost or gained electrons. It can be helpful in determining which atoms will interact or bond with each other. Element Oxidation Number Magnesium Mg +2 Oxygen O -2 Hydrogen H +1 or -1 Chemical Bonding Chemical bonding is the force that acts between two or more atoms to hold them together as a stable molecule. There are three major types of bonding: Ionic bonding: the transfer of valence electrons between atoms. Metallic bonding: the sharing of valence electrons between metal atoms. Covalent bonding: the sharing of valence electrons between non-metal atoms. Ionic Bonding Ionic bonding is the transfer of valence electrons between atoms, resulting in the formation of ions with opposite charges. The oppositely charged ions are attracted to each other and form a stable molecule. Ionic bonds are formed between metal cations and non-metal anions. Page 2  Created by Turbolearn AI Conditions for Formation of Ionic Bond The formation of an ionic bond requires: 1. Number of valence electrons: the atom that loses electrons should have 1, 2, or 3 valence electrons, while the atom that gains electrons should have 5, 6, or 7 valence electrons. 2. Net lowering of energy: the formation of an ionic compound should result in a net release of energy. 3. Electronegativity difference: the difference in electronegativity between the two atoms should be greater than 2. Factors Governing the Formation of Ionic Bond The formation of an ionic bond is governed by several factors, including: Ionization energy: the energy required to remove an electron from an atom. Electron affinity: the energy released when an electron is added to an atom. Lattice energy: the energy released when ions combine to form a solid compound. Factor Description Ionization energy The energy required to remove an electron from an atom. Electron affinity The energy released when an electron is added to an atom. Lattice energy The energy released when ions combine to form a solid compound. These factors determine the strength and stability of an ionic bond.## Ionic Compounds Ionic compounds are formed when one or more electrons are transferred between atoms, resulting in the formation of ions with opposite charges. These ions are held together by electrostatic forces in a crystal lattice. Examples of Ionic Compounds Some examples of ionic compounds include: Page 3  Created by Turbolearn AI Sodium Chloride NaCl: formed from the transfer of one electron from a sodium Na atom to a chlorine Cl atom, resulting in the formation of Na+ and Cl- ions. Magnesium Chloride MgCl2: formed from the transfer of two electrons from a magnesium Mg atom to two chlorine Cl atoms, resulting in the formation of Mg2+ and 2Cl- ions. Calcium Oxide CaO: formed from the transfer of two electrons from a calcium Ca atom to an oxygen O atom, resulting in the formation of Ca2+ and O2- ions. Aluminium Oxide Al2O3: formed from the transfer of three electrons from an aluminium Al atom to three oxygen O atoms, resulting in the formation of 2Al3+ and 3O2- ions. Characteristics of Ionic Compounds The characteristics of ionic compounds include: Solids at room temperature: due to the strong electrostatic forces between the ions. High melting points: due to the strong electrostatic forces between the ions. Hard and brittle: due to the strong electrostatic forces between the ions. Soluble in water: due to the ability of water molecules to detach the ions from the crystal lattice. Conductors of electricity: in the molten state or in aqueous solutions, due to the ability of the ions to move freely. Do not exhibit isomerism: due to the non-rigid and non-directional nature of the ionic bond. Covalent Bonding Covalent bonding occurs when two or more atoms share one or more pairs of electrons to form a covalent bond. Definition of Covalent Bond A covalent bond is a chemical bond that involves the sharing of one or more pairs of electrons between two atoms, resulting in a stable molecule. Page 4  Created by Turbolearn AI Conditions for Formation of Covalent Bond The conditions for the formation of a covalent bond include: Number of valence electrons: each atom should have 5, 6, or 7 valence electrons to achieve a stable octet. Equal ornearequal electronegativity: the atoms should have equal or near equal electronegativity to facilitate electron sharing. Equal sharing of electrons: the atoms should have equal or near equal electron affinity to facilitate equal sharing of electrons. Examples of Covalent Compounds Some examples of covalent compounds include: Hydrogen H2: formed from the sharing of one pair of electrons between two hydrogen atoms. Methane CH4: formed from the sharing of four pairs of electrons between one carbon atom and four hydrogen atoms. Water H2O: formed from the sharing of two pairs of electrons between one oxygen atom and two hydrogen atoms. Types of Covalent Bonds The types of covalent bonds include: Type of Bond Number of Electrons Shared Single Bond 2 Double Bond 4 Triple Bond 6 Types of Overlapping and Nature of Covalent Bond The types of overlapping and nature of covalent bond include: Page 5  Created by Turbolearn AI Sigma σ Bond: formed from the end-to-end overlapping of atomic orbitals along the internuclear axis. Pi π Bond: formed from the side-by-side overlapping of atomic orbitals perpendicular to the internuclear axis. Examples of Sigma σ Bond Some examples of sigma σ bond include: ss Overlapping: between two s-orbitals, such as in the formation of hydrogen molecule H2. sp Overlapping: between an s-orbital and a p-orbital, such as in the formation of hydrogen fluoride HF. pp Overlapping: between two p-orbitals, such as in the formation of fluorine molecule F 2.## Formation of Covalent Bonds Covalent bonds are formed when two or more atoms share one or more pairs of electrons in order to achieve a stable electronic configuration. The formation of covalent bonds can be explained by the overlap of atomic orbitals. Formation of HCI Molecule The formation of the HCI molecule involves the overlap of the 1s orbital of the Hydrogen atom with the 3p orbital of the Chlorine atom. This overlap leads to the formation of a sigma σ bond. Formation of Oxygen Molecule The formation of the Oxygen molecule involves the overlap of the 2p orbitals of two Oxygen atoms. This overlap leads to the formation of a sigma σ bond and a pi π bond, resulting in a double bond. Formation of Nitrogen Molecule The formation of the Nitrogen molecule involves the overlap of the 2p orbitals of two Nitrogen atoms. This overlap leads to the formation of a sigma σ bond and two pi π bonds, resulting in a triple bond. Page 6  Created by Turbolearn AI Differences Between Sigma and Pi Bonds The main differences between sigma σ bonds and pi π bonds are: Sigma σ Bond Pi π Bond Formed by end-to-end overlapping Formed by the sidewise Formation of half-filled atomic orbitals overlapping of half-filled p-orbitals Overlapping takes place Overlapping takes place along the Overlapping perpendicular to the internuclear internuclear axis axis Strength Stronger than pi bonds Weaker than sigma bonds Free rotation about the sigma bond No free rotation about the pi bond Rotation is possible is possible Unequal Sharing of Electrons When two atoms with different electronegativities share a pair of electrons, the electrons are not shared equally. This results in the formation of a polar covalent bond. A polar covalent bond is a covalent bond in which the electrons are not shared equally between the two atoms, resulting in a partial positive charge on one atom and a partial negative charge on the other atom. Examples of Polar Covalent Bonds Water molecule H2O: The oxygen atom has a higher electronegativity than the hydrogen atoms, resulting in a polar covalent bond. Ammonia molecule NH3: The nitrogen atom has a higher electronegativity than the hydrogen atoms, resulting in a polar covalent bond. Hydrogen fluoride molecule HF : The fluorine atom has a higher electronegativity than the hydrogen atom, resulting in a polar covalent bond. Nonpolar and Polar Molecules A nonpolar molecule is a molecule in which the atoms are arranged in a symmetrical shape, resulting in no net dipole moment. A polar molecule is a molecule in which the atoms are arranged in an asymmetrical shape, resulting in a net dipole moment. Page 7  Created by Turbolearn AI Characteristics of Nonpolar and Polar Molecules Nonpolar molecules: Have a symmetrical shape Have no net dipole moment Are less reactive than polar molecules Polar molecules: Have an asymmetrical shape Have a net dipole moment Are more reactive than nonpolar molecules Dipole-Dipole Interactions Dipole-dipole interactions are weak intermolecular forces that occur between two polar molecules. These interactions are responsible for the physical properties of polar molecules, such as their boiling and melting points. Characteristics of Covalent Compounds Covalent compounds have the following characteristics: Low melting and boiling points: Covalent compounds have low melting and boiling points due to the weak intermolecular forces between the molecules. Solubility in organic solvents: Covalent compounds are soluble in organic solvents due to the similar intermolecular forces between the solvent and solute molecules. Insolubility in water: Covalent compounds are generally insoluble in water due to the lack of hydrogen bonding between the molecules. Non-conductivity of electricity: Covalent compounds do not conduct electricity due to the lack of ions in the molecule. Coordinate Covalent Bond A coordinate covalent bond is a covalent bond in which both electrons of the shared pair come from one of the two atoms. A coordinate covalent bond is a covalent bond in which one atom donates a pair of electrons to another atom, resulting in a shared pair of electrons. Page 8  Created by Turbolearn AI Examples of Coordinate Covalent Bonds Ammonia molecule NH3: The nitrogen atom donates a pair of electrons to the hydrogen atoms, resulting in a coordinate covalent bond. Water molecule H2O: The oxygen atom donates a pair of electrons to the hydrogen atoms, resulting in a coordinate covalent bond. Hydrogen Bonding Hydrogen bonding is a strong intermolecular force that occurs between a hydrogen atom bonded to a highly electronegative atom (oxygen, nitrogen, or fluorine) and another electronegative atom. Hydrogen bonding is an electrostatic attraction between a hydrogen atom bonded to a highly electronegative atom and another electronegative atom, resulting in a strong intermolecular force. Characteristics of Hydrogen Bonding Strong intermolecular force: Hydrogen bonding is a strong intermolecular force that is responsible for the physical properties of molecules, such as their boiling and melting points. Occurs between highly electronegative atoms: Hydrogen bonding occurs between a hydrogen atom bonded to a highly electronegative atom (oxygen, nitrogen, or fluorine) and another electronegative atom. Results in long chains or clusters of molecules: Hydrogen bonding results in the formation of long chains or clusters of molecules, which are responsible for the physical properties of the molecules.## Conditions for Hydrogen Bonding The necessary conditions for the formation of hydrogen bonding are: High electronegativity of atom bonded to hydrogen Small size of electronegative atom Hydrogen bonding is a type of intermolecular force that arises between molecules with a hydrogen atom bonded to a highly electronegative atom, such as oxygen, nitrogen, or fluorine. The electronegative atom attached to the hydrogen atom by a covalent bond should be quite small, resulting in a high polarity of the bond between the hydrogen atom and the electronegative atom. Page 9  Created by Turbolearn AI Examples of Hydrogen-Bonded Compounds Some examples of hydrogen-bonded compounds include: Hydrogen Fluoride HF : contains the strongest polar bond, with the electronegativity of fluorine being the highest of all elements Water H2O: each hydrogen atom can hydrogen bond to the oxygen atom of another molecule, forming large chains or clusters of water molecules Ammonia NH3: each hydrogen atom can hydrogen bond to the nitrogen atom of other molecules Types of Hydrogen Bonding There are two types of hydrogen bonding: 1. Intermolecular Hydrogen Bonding: formed between two different molecules of the same or different substances 2. Intramolecular Hydrogen Bonding: formed within the same molecule Characteristics of Metals Metallic bonding is characterized by: Low ionization energies, implying that the valence electrons in metal atoms can easily be separated A number of vacant electron orbitals in their outermost shell Electric conductivity, with mobile electrons free to move through the vacant space between metal ions Heat conductivity, with mobile electrons absorbing heat energy and transferring it to adjacent electrons Ductility and malleability, with the sea of electrons adjusting positions rapidly and the crystal lattice being restored Exceptions to the Octet Rule Some molecules have non-octet structures, with atoms having a number of electrons in the valence shell short of the octet or in excess of the octet. Examples include: Page 10  Created by Turbolearn AI Compound Number of Electrons around Central Atom Beryllium Chloride BeCl2 4 Boron Trifluoride BF 3 6 These compounds are referred to as electron-deficient compounds. Page 11