Bonding & Structure

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  • Created by: goliver3
  • Created on: 18-01-17 12:07

Types of Bond

  • An ionic bond is an attraction between oppositely charged ions which are formed by the transfer of electrons from one atom to another
  • A covalent bond is a pair of electrons shared between two atoms
  • A dative covalent bond is a pair of electrons shared between two atoms, one of which provides both electrons to the bond
  • A dative covalent bond is represented by a short arrow from the electron pair providing atom to the atom providing neither
  • A metallic bond is an attraction between cations and a sea of electrons
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Ionic Or Covalent? (Electronegativity)

  • Electronegativity is the relative ability of an atom to attract electrons in a covalent bond
  • Electronegativity increases across a period as the nuclear charge on the atoms increase but the shielding stays the same
  • Electronegativity decreases down a group as the number of shells increase, therefore so does the shielding
  • An atom with high electronegativity is electronegative
  • An atom without high electronegativity is electropositive
  • If both atoms have electronegativities less than 1.9 then the bond is metallic
  • If either atom has an electronegativity greater than 1.9 and the difference is less than 0.5 then the bond is covalent
  • If the difference is more than 0.5 but less than 2.1 then the bond is polar covalent
  • If the difference is greater than 2.1 then the bond is ionic
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Ionic Structures

  • Ions in ionic bonds come together to form a lattice
  • In a lattice all the anions are surrounded by cations and vice versa
  • The attraction between opposite ions is very strong, making the boiling/melting point of ionic compounds very high
  • The higher the charge on the ions, and the smaller they are, the stronger the attraction
  • Ionic lattices cannot conduct electricity when solid as the ions are locked in place
  • Ionic lattices can conduct electricity when liquid as the ions are free to move
  • Ionic lattices are hard and brittle as ions cannot move or slip over eachother easily
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Metallic Structures

  • Metallic bonding is the attraction between cations and a sea of delocalised electrons
  • The cations are arranged in a lattice with the electrons free to move between them
  • The melting/boiling point of metallic structures is generally lower than ionic structures, whilst still being high 
  • Smaller ions, and those with a high charge, attract electrons more strongly and therefore have higher melting/boiling points
  • The metal cations slide over eachother and therefore metallic structures are soft, malleable, and ductile
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Intermolecular Forces

  • There are 3 types of intermolecular forces
  • Van der Waal's forces
    • Caused when electrons move to one side of a molecule more than another (temporary dipole), which then causes an induced dipole in an adjacent molecule
    • Can be found in every molecule - weakest intermolecular force
    • The more electrons in the molecule, the greater the likelihood of a temporary dipole forming
    • The larger the surface area of the molecule, the more contact it will have with adjacent molecules, therefore the greater the chance of a dipole being induced
  • Permanent dipole
    • Found in polar molecules
    • Stronger than van der waal's forces
  • Hydrogen bonding
    • Found when hydrogen has a direct bond with Nitrogen, Oxygen, or Fluorine (NOF)
    • Strongest intermolecular force
    • Due to hydrogen being electropositive and NOF being very electronegative
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