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Chemical bonding by Ms Rashmi Bhatia
 

Chemical bonding by Ms Rashmi Bhatia

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A presentation to teach chemial bonding easily.

A presentation to teach chemial bonding easily.

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    Chemical bonding by Ms Rashmi Bhatia Chemical bonding by Ms Rashmi Bhatia Presentation Transcript

    • CHEMICAL BONDING
      • Category: Secondary
      • Name: Ms. Rashmi Bhatia
      • Subject: Chemistry
      • Topic of e-lesson: Chemical Bonding
      • Class/Target Group:
      • Class 10 th
      • The students will be able to
      • Define Chemical Bonding
      • Differentiate between Ionic and Covalent Bonding.
      • Understand the concept of Chemical Bonds by relating it to everyday life.
      • Draw Lewis dot structures showing different type of bonds.
      • Explain all the types of Bonds.
      • List the various properties of Ionic and Covalent Compounds.
      • Appreciate different diagrammatic representations of Bonds.
      Learning Objectives
    • Marriage Divorce Forming of a bond is like marriage
      • More stable
      • Exothermic
      The breaking of a bond relates to a divorce .
      • Less stable
      • Endothermic
    • What is a Chemical Bond?
      • A Chemical Bond may be defined as the force of attraction which holds various constituents entities (atoms or ions) together in different chemical substances.
      • Compounds are formed from chemically bound atoms or ions.
      • Bonding involves only the valence electrons.
    • STUDY OF CHEMICAL BONDING
          • Linus Pauling, winner of two Nobel Prizes, developed innovative techniques to investigate chemical bonding and molecular structure. He won his first Nobel Prize for his investigation of genetic chemistry, and the second for his dedicated efforts to stop nuclear weapons testing.
    • Why Are Chemical Bonds Formed ?
      • Chemical bonds are formed to lower the energy of the system, the components of the system become more stable through the formation of bonds.
      • Everything wants to be more stable - its easy to lie down than stand up, bonding is Nature's way of allowing the elements to lie down.
      • If we examine the periodic table, we find that the elements in Group VIII (or 18), helium, neon, argon and so on, are particularly stable, so much so that they were once labeled the "inert gases".
      • G. N. Lewis (1916) suggested that bonds (covalent) formed to enable elements to attain this "noble gas configuration" .
      • We can see that in each case, sharing or transfer of electrons, results in a more stable system.
    • Drawing Lewis Structures
      • Sum the valence electrons from all atoms. Add one for each negative charge and subtract one for each positive charge.
      • Draw a skeleton structure with atoms attached by single bonds.
      • Complete the octets of atoms bound to the central atom.
      • Place extra electrons on the central atom.
      • If the central atom doesn’t have an octet, try forming multiple bonds .
      • It was observed that the electron configuration of many substances after ion formation was that of an inert gas  octet rule.
      • E.g. The electron configuration of each reactant in the formation of NaCl gives:
        • Na+ is that of [Ne]
        • Cl  is also that of [Ar ].
    • WHY DO ATOMS BOND TOGETHER?
      • TO ATTAIN STABILITY
      • TO COMPLETE THE OCTET
      • TO FORM MOLECULES
      • TO ACHIEVE THE NOBLE GAS CONFIGURATION .
    • Electronic Configuration of first twenty elements.. Atoms tend to gain or lose their outer electrons to achieve a ‘full’ valence shell. INERT- GAS CONFIGURATION The outermost shell of the noble gas atoms are completely filled due to the presence of eight electrons (two in case of Helium).
    • Just as a summary to what each bond looks like…
    • Bonding by Analogy: Dog - Bone Bonds
      • One big greedy thief dog!
      • Dogs of equal strength.
      • Unevenly matched but willing to share
      • The chemical bond formed by the transfer of electrons from one atom to another is known as ELECTROVALENT OR IONIC BOND.
      • For example: NaCl,KCl,MgCl 2 ,MgO, CaO, NH 4 Cl, CaCl 2 , etc.
      • When is an Ionic Bond Formed?
      • An ionic bond is formed when a cation (positive ion) transfers electrons to an anion (negative ion).
      IONIC BONDING
    • Characterstics of Ionic Bonds
      • Metal atoms always lose their valence (outer) electron to form positive Ions or cations.
      • Non-Metals atoms always gains electrons to form negative ions or anions.
      • Thus Ionic Bonds result from the attraction between the oppositely charged ions.
    • FORMATION OF IONIC BOND IN SODIUM CHLORIDE (NaCl):
      • The electronic configuration of sodium (Na) is 2,8,1.The Na atom donates its outermost electron to attain the stable inert gas configuration and forms Na +.
      • The electronic configuration of Cl is 2,8,7. The Cl atom takes one electron (from Na atom) to form a negatively charged ion Cl - .
      Ionic bond has formed a Sodium Chloride molecule: - Structural formula: Na-Cl - Molecular formula: NaCl
    • Bond formation in NaCl
    • Examples of Ionic Bond
    • STRUCTURE OF NaCl CRYSTAL:--
          • The scanning electron micrograph shows pure salt, or sodium chloride, that has been recrystallized from distilled water. The crystal is built up from a cubic lattice of sodium and chloride ions.
    • COVALENT BONDING :
      • The chemical bond formed by sharing of electrons between two atoms in such a way that each atom in the resulting molecule gets the stable electron arrangement of an inert gas. This is COVALENT BOND .
      • For example: Cl 2 , HCl , CH 4 ,CO 2 , N 2 , C 2 H 2 , etc.
      What forms a Covalent Bond? A covalent bond is formed between two nonmetals. WATER OXYGEN METHANE
    • TYPES OF COVALENT BONDS
      • Covalent Bonds are of three types :------
      • 1. Single Covalent Bond For eg; Cl 2 , H 2 , CH 4 ,HCl , NH 3 , H 2 o , etc.
      • 2. Double Covalent Bond For eg ; CO 2 , O 2 ,
      • C 2 H 4 , etc.
      • 3. Triple Covalent Bond For eg ; N 2 , C 2 H 2 , etc.
      O 2 N 2 H 2 O
    • Examples of Covalent Bond
    • Lewis –Dot Structures of some Covalent Compounds
    • FORMATION OF A SINGLE COVALENT BOND IN Cl 2 :
      • A single covalent bond is formed by the sharing of one pair of electrons between two atoms .
      • Cl has electronic configuration of 2,8,7; has 7 valence electrons so it needs 1 more electron to achieve the 8- electron inert gas configuration.
      • Thus, both the Cl atoms will become stable by sharing 1 electron with each other.
      - Covalent bond has formed a chlorine molecule: - Structural formula: Cl-Cl - Molecular formula: Cl 2
      • If the atoms participating in the covalent bond formation are the same, the molecules are called Homoatomic Molecules.
      • H has electronic configuration of 1; has only one valence electrons so it needs 1 more electron to achieve the 2- electron inert gas configuration of Helium.
      • Thus, both the H atoms will become stable by sharing 1 electron with each other.
      - Covalent bond has formed a hydrogen molecule: - Structural formula: H-H - Molecular formula: H 2 Indicates one covalent bond Covalent bond in Homoatomic Molecules
      • If the atoms participating in the Covalent bond formation are different, then these are called Heteroatomic molecule
      • Hydrogen atom has 1 valence electron so it needs 1 more electron to get Helium gas electron structure and become stable.
      • Oxygen atom has 6 valence electrons,so it needs 2 more electrons to achieve the 8- electron stable structure .
      • Thus, both H & O will become stable by sharing 1 electron with each oxygen atom.
      H Covalent bonds give each atom a full complement of valence electrons ! A Water molecule O H Covalent bond in Hetero-atomic molecule …. Water !
    • FORMATION OF DOUBLE COVALENT BOND IN CO 2 :--
      • A double covalent bond is formed by the sharing of 2 pairs of electrons between 2 atoms.
      • C has electronic configuration of 2,4 , has 4 valence electrons so it needs 4 more electrons to achieve the 8- electron inert gas configuration.
      • O has electronic configuration of 2,6, has 6 valence electrons so it needs 2 more electrons to achieve the 8- electron inert gas configuration
      • So 2 Oxygen atoms combine together with C by sharing 2 electrons each to form a molecule of CO 2 gas .
    • FORMATION OF TRIPLE COVALENT BOND IN NITROGEN (N 2 ) :---
      • A Triple Covalent bond is formed by the sharing of three pairs of electrons between two atoms.
      • The electronic configuration of N is 2,5 has 5 valence electrons, so it needs 3 more electrons to achieve the 8- electron structure of an inert gas & attain stability.
      • So 2 Nitrogen atoms combine together by sharing 3 electrons each to form a molecule of Nitrogen gas.
    • We are going to look at Polar Covalent now… What is polar covalent bond? - Polar covalent is a description of a bond that has an uneven distribution of charge due to an unequal sharing of bonding electrons. The boy is not equally sharing with anyone else but rather taking all the food for himself.
    •  
    • Polar Covalent Bond One atom is more electronegative than the other. Example: water molecule
    • Properties of Ionic Compounds
      • Physical Nature : Are solids which are in the form of crystals and relatively hard because of strong electrostatic force of attraction between oppositely charged ions and consequent close packed structure. These compounds are generally brittle and break into pieces when subjected pressure and stress. eg.the crystal lattice of NaCl has been already shown.
      • Melting and Boiling Points : As the ions in the ionic compounds are closely held together by strong interionic attractions, the solid ionic compounds are generally crystalline. A considerable energy is required to break the close packed crystalline structure and hence both melting and boiling points are high.
      • For e.g.when sodium chloride is added in water .,each Na+ ion and Cl- ion is surrounded by a number of molecules of water(H2O) which also carry charge. And are called Hydrated ions.
      • NaCl(s) +H 2 O
      • Na + (aq)+Cl - (aq)
      3) Solubility : Ionic compounds are generally soluble in polar solvents like water and insoluble in non-polar solvents, or less polar solvents like alcohol, ether, benzene, etc.
    • 4 ) Electrical Conductivity : The conductance through metals is because of movement of valence electrons. Since movement of ions and ionic solids is not possible due to the rigid structure, ionic compounds in the solid state either do not conduct electricity or are poor conductors. However, in the molten state or aqueous solution, ionic compounds conduct electricity due to mobility of ions.
    • Properties of Covalent Compounds
      • Physical State : Covalent compounds can exist as solids, liquids or gases (mostly gases).
      • Solubility : Covalent compounds are generally soluble in non-polar solvents, or less polar solvents like alcohol, ether, benzene, etc. generally and insoluble in polar solvents like water.
      • Melting and Boiling Points : Molecules of an covalent compound are held together by relatively weaker forces as compared to that of ionic compounds. Therefore, melting and boiling points of covalent compounds are
    • generally low, as less energy is required to overcome these weak forces. 4) Electrical Conductivity : covalent compounds are poor conductors of electricity because they neither contain the ions nor the free electrons necessary for conduction. For example, Hydrogen Chloride gas i.e. HCl (g) is a poor conductor of electricity. But in water, it changes into hydrochloric acid i.e. HCl(aq). Since the acid can ionise in solution to form H+ and Cl- ions, it becomes a good conductor of electricity.
    • THANK YOU AND HAVE A NICE DAY!!!
          • The ionic bond is a form of chemical linking of atoms in which electrons are transferred from one atom to another so that both atoms end up with completely filled electron shells. The alkali metals, such as potassium, shown here, have a single electron occupying the outermost shell in the atom. This is readily lost to halogen atoms, which require a single electron to fill their outermost shells. When the electron, which has a negative electrical charge, has been transferred, the alkali metal atom has become a positively charged ion, while the halogen atom has become a negatively charged ion. The two ions are held together strongly by electrostatic attraction.
      IONIC BOND CONTD…..
    • IONIC BONDING IN POTASSIUM CHLORIDE( KCl )