Bonding

• What are cations?

  Positive ions
• What are anions?

  Negative ions
• When do ionic compounds conduct electricity?

  When dissolved in water or molten. Ions in liquid free to move & carry charge. In solid, ions fixed in position by strong ionic bonds.
• Why do ionic compounds have high mp?

  Giant ionic lattices held together by strong electrostatic forces. Lots of energy needed to overcome.
• Why do ionic compounds tend to dissolve in water?

  H20 molecules polar, so pull ions away from lattice and cause it to dissolve.
• What is a co-ordinate bond?

  Covalent bond that forms when 1 of the atoms in the bond has a lone pair of electrons, & the other doesn't have any electrons available to share.
• What are the properties of diamond?

  High melting point, hard, insoluble, can't conduct electricity as outer electrons held in localised bonds, and good thermal conductor as vibrations travel easily through stiff lattice.
• What is the structure of diamond?

  Giant covalent structure. Each carbon atom covalently bonded to 4 other carbon atoms. Atoms arrange in a tetrahedral shape. Strong covalent bonds between atoms.
• What is the structure of graphite?

  Carbon atoms arranged in sheets of flat hexagons covalently bonded with 3 bonds each. 4th outer electron of each carbon is delocalised. Sheets of hexagons bonded together by weak van der Waals forces.
• What are the properties of graphite?

  Slippery due to sheets sliding over eachother as there are weak IMF between layers that are easily broken. Can conduct electricity due to delocalised electrons. Low density as layers far apart compared to covalent bond length. High mp due to covalent bonds and insoluble.
• Why is graphite used as dry lubricant and in pencils?

  Weak bonds ( van der Waals) between layers easily broken, so sheets can slide over eachother. Makes it slippery.
• What is a charge cloud?

  A region in an atom where an electron is likely to be found.
• What do the shapes of molecules & molecular ions depend on?

  Number of pairs of electrons in outer shell of their central atom. Bonding pairs & lone pairs exist as charge clouds.
• Why do charge clouds repel eachother?

  Electrons are negatively charged. Lone pair charge clouds repel more than bonding pair charge clouds, so bond angles often reduced as bonding pairs pushed together by lone-pair repulsion.
• 2 bonding pairs & no lone pairs of electrons


  Linear- 180 degrees bond angle.
• 3 bonding pairs & no lone pairs of electrons

  Trigonal planar- 120 degrees bond angle.
• 2 bonding pairs & 1 lone pair of electrons

  Non-linear / bent. Bond angle a bit less than 120 degrees. ( Each lone pair decreases bond angle by about 2.5 degrees).
• 4 bonding pairs & no lone pairs of electrons

  Tetrahedral- 109.5 degrees bond angle.
• 3 bonding pairs & 1 lone pair of electrons

  Trigonal pyramidal- 107 degrees bond angle. Smaller bond angles between bonding pairs & larger bond angles between lone pair & bonding pairs.
• 2 bonding pairs & 2 lone pairs of electrons

  Bent/ non-linear- 104.5 degrees bond angle.
• 5 bonding pairs & no lone pairs of electrons

  Trigonal bipyramidal. 3 atoms form trigonal planar with angles of 120 degrees, other 2 atoms will be at 90 degrees to them.
• 4 bonding pairs & 1 lone pair of electrons


  Seesaw shape. Lone pair positioned where 1 of trigonal planar atoms would be in trigonal bipyramidal molecule.
• 3 bonding pairs & 2 lone pairs of electrons

  T-shaped molecule. 87.5 degrees.
• 6 bonding pairs & no lone pair of electrons.

  Octahedral. 90 degrees bond angles.
• 5 bonding pairs & 1 lone pair of electrons


  Square pyramidal structure (rare).
• 4 bonding pairs & 2 lone pairs of electrons


  Square planar.
• What is electronegativity?

  Ability to attract the bonding electrons in a covalent bond. Measured on Pauling scale.
• What is a non-polar bond?

  Atoms in bond have equal or similar electronegativities, so electrons are equally attracted to both nuclei.
• What is a polar bond?

  In covalent bond between 2 atoms of different electronegativities, bonding electrons are pulled towards more electronegative atom. Greater the difference in electronegativity, the more polar the bond.
• What is a dipole?

  Difference in charge between the 2 atoms caused by a shift in electron density in the bond.
• What is a permanent dipole?

  Charge distributed unevenly across whole molecule.
• What are Van der Waals forces?

  Weakest IMF. Electrons in charge clouds move quickly so likely to be more to 1 side than the other- atom has temporary dipole. Dipole causes another temporary dipole in opposite direction on a neighbouring atom. 2 dipoles attracted to eachother- can cause another dipole in 3rd atom. Dipoles created & destroyed constantly.
• Metal conductivity

  Delocalised electrons can pass kinetic energy to eachother, making metals good thermal conductors. Good electrical conductors as delocalised electrons can move & carry a charge.
• Metal solubility

  Insoluble, except in liquid metals, due to strength of metallic bonds.
• Describe a gas

  Particles have more energy & are further apart. Low density & very compressible. Particles move freely, not a lot of attraction between them, so quickly diffuse to fill a container.
• What are physical properties determined by?

  Mp & bp determined by strength of attraction between particles. Only conducts electricity if it contains charged particles free to move. Polar or charged substances dissolve in water well.
• Describe a liquid

  Similar density to solid, virtually incompressible, particles move freely & randomly within liquid, allowing it to flow.
• Describe a solid

  Particles very close together, high density & incompressible, vibrate about fixed point & can't move freely.
• Metallic bonding

  Metal elements exist as giant metallic lattice structures. Outermost shell of metal atom delocalised- leaves positive metal ion. Positive metal ions attracted to delocalised negative electrons. Forms lattice of closely packed positive ions in sea of delocalised electrons.
• Why are metals malleable & ductile?

  No bonds holding specific ions together, so metal ions can slide over eachother when structure is pulled, so metals malleable (shapeable) & ductile (drawn into wire).