Bonding and Structure

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  • Created by: Sophie
  • Created on: 27-01-14 21:29

Introduction

Introduction

  • Atoms form bonds to get a full outer shell of electrons.
  • There are three types of bonding:
    • Ionic bonding
    • Covalent bonding
    • Metallic bonding
  • To conduct electricity there much be charged that can move (ions or electrons).
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Types of Bonding - Ionic Bonding

Ionic Bonding

  • Ionic Bond - Electrostatic attraction between opposutley charged ions.
  • In ionic bonding, metals transfer electrons to non-metals producing positive metal ions and negative non-metal ions.
  • Dot-cross diagrams show outer elctrons only.

Example

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Types of Bonding - Covalent Bonding

Covalent Bonding

  • Covalent bond - is a chemical link between two atoms in which electrons are shared between them.
  • Ony non-metals can get a full shell by sharing electrons.

Example

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Types of Boning - Dative Covalent Bonds

Dative Covalent Bonds

  • Dative bond - Is a covalent bond between two atoms where one of the atoms provides both electrons that form the bond.
  • One atom provides both of the shaired pair of electrons.

Example


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Types of Boning - Metallic Bonding

Metallic Bonding

  • Metallic Bond - Electrostatic attraction between positive ions and delocalised electrons.
  • Metals lose their outer shell electrons to produce a lattice of positive metal ions surrounded by delocalised electrons.

Example

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Types of Structure - Giant Ionic Lattices

Giant Ionic Lattices

  • The lattice is made up of oppositely charged ions.
  • It has a high melting and boiling point (strong forced of attraction between ions need to be broken).
  • Do not conduct when solid (iosn not free)
  • Conduct when molten or dissolved in water.
  • An example, Sodium Chloride.
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Types of Structure - Simple Covalent Lattices

Simple Covalent Lattices

  • Consists of molecules held together by weak intermolecular forces.
  • Low melting and boiling points (weak forces of attraction between molecules are easily broken).
  • Do not conduct (no mobile charge carriers).
  • Example - Iodine and ice.
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Types of Structure - Giant Metallic Lattices

Giant Metallic Lattices

  • Lattice of metal ions surrounded by delocalised electrons.
  • High melting and boiling points (stron forces of attraction between metal ions and free electrons).
  • Conduct when solid (free electrons)
  • Example - Magnesium and Copper
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Types of Structure - Giant Covalent Lattices

Giant Covalent Lattices

  • Lattice of non-metal atoms joined by strong covalent bonds.
  • Very high melting and boiling point.
  • Diamond does not conduct (no free electrons).
  • Graphite is the only non-metal that conducts as a solid (contains delocalised electrons).
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Electronegativity and Bond Polarity

Electronegativity and Bond Polarity

  • Electronegativity - A property of an atom which increases with its tendency to attract the electrons of a bond.
  • If there is a big difference in electronegativity between the atoms the electrons will be pulled towards the more electronegative atom.
  • The most electronegative elements are Fluorine, Chlorine, Oxygen and Nitrogen.
  • Polar molecules have permanent dipoles that don't cancel out.
  • Non-polar molecules either have no dipole or temporary dipoles that cancel out.

Example

  • Chlorine is more electronegative than hydrogen.

    δ+   δ-

    H-Cl


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Intermolecular Forces - Van der Waal's

Van der Waal's

  • Van der Waal's - Are the weak forces which contribute to intermolecular bonds.
  • Arise from temporary dipole (uneven distribution of electrons) in one molecule that iduces dipole in another molecule.
  • The more electrons, the stronger the Van der Waal's forces.
  • Occur in all simple covalent substances.
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Intermolecular Forces - Dipole-dipole

Dipole - dipole

  • Dipole - separation of electrical charges.
  • Attraction between molecules with permanent dipoles.
  • δ+ ends attracted to δ- ends.
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Intermolecular Forces - Hydrogen bonds

Hydrogen Bonds

  • Hydrogen Bond - is a type of attractive interaction between electronegative atom and a hydrogen atom bonded to another electronegative atom.
  • Need H attached to N/O/F.
  • Exposed H nulceus is strongly attracted to lone pair on N/O/F.

Diagram

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Intermolecular Forces - Anomalous properties of wa

Anomalous properties of water

  • Water has some unusual properties due to the presence of hydrogen bonding:
    • Ice is less dense than water because ice has an open structure.
    • Water has a high melting and boiling point than expected due to the strength of hydrogen bonds that have to be broken.
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Shapes of Molecules

Shapes of Molecules

  • Pairs of electrons reoek each other and get as far apart as possible.
  • Lone pairs repel more than bonding pairs - they change the angle by 2.5°.

Table

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