Bonding

• what are the 3 main factors affecting the strength of metallic bonding?

  • nuclear charge
  • number of delocalised electrons per atoms
  • Size of ion
• What are the properties of ionic compounds?

  • high melting and boiling point because of giant lattice of ions with strong electrostatic forces between oppositely charged ions requires lots of energy to break
  • Poor conductors of electricity when solid
  • can conduct when molten or aqueous as ions are free to move and carry charge
• What are the most electronegative atoms?

  Fluorine, oxygen, nitrogen, chlorine
• Explain why nickel is ductile


  Layers of atoms are able to slide over each other
• How does the precense of lone pairs affect bond angles?

  2.5o for each lone pair
• Describe the structure of Iodine


  Regular arrangement of molecules held together by weak VDW forces 
• State the meaning of the term electronegativity

  The power of an atom or nucleus to withdraw or attract a pair of electrons in a covalent bond
• What is electronegativity?


  Electronegativity is the power of an atom to attract bonded electrons in a covalent bond towards itself 
• What are the 3 types of IM forces?

  Van der waals , Dipole-Dipole and hydrogen bonds
• What shape is formed from 3 l.p and 2 b.p?

  Linear 
• How does electronegativity change across a period?

  Electronegativity will increase across a period as the number of protons increases but there is similar shielding. Furthermore, the atomic radius decreases as the electrons in the same shell are pulled in more. 
• Describe permanent dipole-dipole forces

  Electrostatic forces between polar molecules

  Stronger than VDWs so compounds have higher BP
• Explain why the melting point of magnesium is higher than that of sodium

  • Mg2+ have a higher charge than Na+
  • Shorter distance between e- and ions in Mg2+
  • Hence stronger metallic bonding
• Suggest why the electronegativity of the elements increases from lithium to fluorine

  • More protons mean there is a bigger nuclear charge
  • There is the same or similar shielding
• Describe the structure of graphite

  trigonal planar arrangement of carbon in layers

  3 covalent bonds per atom in each layer, 4th is delocalised 
• State 5 properties of metals


  high mp/bp due to strong attraction between +ve ions and sea of delocalised electrons

  insoluble

  good conductors of electricity

  shiny 

  malleable, as layers of ions can slide over each other 
• What structure do ionic structures take?

  Giant Ionic Lattice
• Explain, in terms of the intermolecular forces present in each compound, why HF has a higher boiling point than HCl

  HF has hydrogen bonding

  HCl has permanent dipole-dipole bonding

  Hydrogen bonding is stronger
• What are the 2 conditions for hydrogen bonding to occur?

  • attraciton between lone pair on F,O,N and H
  • H connected to F, O, N
• What shape is made from 4 bond pairs and 2 lone pairs?

  Square Planar
• What is hydrogen bonding?

  The strongest type of IM force that forms between Hydrogen and F, O, N. The lone pair on these atoms attract a hydrogen atom on another molecule. 
• What is a dative covalent bond?

  A dative covalent bond forms when the shared pair of electron in the covalent bond come from only one of the bonding atoms. 
• What is a dipole moment?

  The overall effect of polarity of the bonds in a molecule 
• Use hydrogen bonding to explain why ice floats in water

  Since ice floats in water, it must be less dense than water

  The hydrogen bonds in ice hold the molecules further apart so density is lower whereas in water the hydrogen bonds are constantly breaking and reforming since the molecules move.
• Explain why the second ionisation energy of magnesium is greater than the first ionisation energy of magnesium

  The electron is being removed from a more positive ion with a greater nuclear charge
• What are the 4 types of crystal structures?

  Ionic

  Metallic

  Simple Molecular

  Giant Covalent
• Why is graphite a good conductor of electricity?

  Delocalised electrons can carry charge
• Describe how Van Der Waal's Forces form

  In any molecule, the electrons are moving constantly and randomly. The electron density hence fluctuates and parts of the molecule becomes more or less negative - forming temporary dipoles.

  These temproary dipoles can induce dipoles in neighbouring molecules, which will be of the opposite sign. 

  The electrostatic forces between the induced dipoles are known as Van Der Waal's forces.
• Describe the structure of ice


  molecular structure

  tetrahedral arrangament

  molecules held further apart than in liquid 
• Explain why the melting point of aluminium is higher than the metling point of sodium


  Bigger charge on ions / Smaller Ions / More Protons

  More Delocalised Electrons

  Stronger Metallic Bond / Attraction of the Ions 
• Describe the structure of and bonding in graphite and explain why the melting point of graphite is very high

  • Layers of C atoms
  • Are connected by covalent bonds
  • van der Waals forces between the layers
  • Strong covalent bonds are what are broken during melting
• How does electronegativity change down a gorup?

  Electronegativity will decrease down a group because the distance between the nucleus and bonded electrons increase and the shielding of the inner shell electrons increases. 
• What are the factors affecting Van Der Waal's forces?

  More electrons = stronger VDW forces

  Bigger surface area = Stronger VDW forces 
• Explain, in terms of electronegativity, why the boiling point of H2S2 is lower than H2O2

  • The electronegativity of S is lower than the electronegativity of O
  • The difference between H and S electronegativity is less
  • Hence, S and O have greater delta positive/negative charge, stronger bonds require more energy t obreak
  • There is no hydrogen bonding between the H2S2 molecules, only van der Waals forces
• Describe the properties of simple molecular compounds

   low m.p/b.p because of weak IM forces (VDW)

  poor solubility in water

  poor conducitivity of electricity in solid/when molten as there are no ions / electrons are localised

  generally mostly gases and liquids 
• Describe the bonding in a metal

  • Positive ions
  • Attract delocalised electrons
  • Which are in a free to move ‘sea’
• Explain, in terms of its structure and bonding, why titanium has a high melting point:

  There is strong attraction between the number of protons and delocalised electrons
• Define covalent bonding

  When two atoms share pairs of electrons
• Explain, in terms of structure and bonding, why the melting point of carbon is high:

  • Macromolecular structure is giant
  • Covalent bonds in the structure
  • Are strong and require lots of energy to break/overcome the bonds
• Trigonal planar

  b.p = 3

  l.p = 0

  bond angle = 120