Bonding

Ionic Bonding

  • Occurs between metals and non-metals
  • Electrons transferred from metal atoms to non-metal atoms
  • Positive and negative ions are formed
  • Two oppositely charged ions attracted by electrostatic forces - extends throughout compound so forms a lattice
  • Atoms want to attain noble gas electronic structure 

Properties:

  • Always solid at room temp.
  • Giant structure - high MP
  • Conduct electricity when molten/dissolved
  • Brittle/ shatter easily after sharp blow (may cause shift in lattice causing contact between atoms with like charges)
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Covalent Bonding

  • Two non-metal atoms
  • Electrons are shared to attain noble gas structure
  • Atoms with shared electrons held together by electrostatic attraction between nuclei and shared electrons within the molecule

Double bonds - four electrons are shared

Properties:

  • Low MP as string covalent bonds only between atoms, not between molecules (vdw)
  • Poor conductors as molecules are overall neutral 
  • If they dissolve they remain as molecules
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Co-ordinate Bonding

  • One atom provides both shared electrons (|also called dative covalent bonding)
  • Atom that accepts the electron pair doesn't have filled outer shell (electron-deficient)
  • Atom donating electrons has lone pair of electrons not being used in a bond
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Metallic Bonding

  • Atoms in metal can't transfer electrons unless there's a non-metal present to accept them, so outer shells merge
  • Lattice of positive ions held together by sea of delocalised electrons 
  • Repulsion of positive ions is balanced by electrostatic attraction to negative delocalised electrons

Properties:

  • Good electrical conductors - delocalised electrons free to move throughout structure 
  • Good thermal conductors - energy spread by vigorous vibrations between closely packed ions
  • Malleable and ductile as new shapes are maintained 
  • High MP - giant structure

Strength of metallic bond:

  • Greater charge on ion, more delocalised electrons, stronger electrostatic attraction 
  • smaller ion, delocalised electrons closer to nucleus, stronger attraction
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Polarity of covalent bonds

  • Electrons are not shared equally in a covalent bond between two atoms of different electronegativity
  • Electron cloud distorts towards the more electronegative element
  • Causes one atom to be slightly positive and one slightly negative - polar  
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Forces between molecules

Van der Waals - Between all atoms and molecules

  • Instantaneous/ induced dipoles produce weak electrostatic attractions
  • Vdw forces can be in addition to other intermolecular forces
  • Causes changes in the shape of electron clouds, so the more electrons there are the stronger the vdw

Dipole-dipole forces - Molecules with a polar bond may have a dipole moment, summing up the effect of the polarity of all bonds in the molecule

  • molecules with more than one polar bond can cancel out (no dipole moment) or they can add up and reinforce each other (based on shape)
  • dipole-dipole forces act between molecules with permanent dipoles

Hydrogen bonding - Hydrogen atom between two very electronegative atoms, must have a highly electronegative atom with lone pair covalently bonded to a hydrogen (lone pair attracted to electron deficient hydrogen)

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