Electrons and Bonding

• How many electrons are in the first 4 shells?

  1 - 2 electrons

  2 - 8 electrons

  3 - 18 electrons

  4 - 32 electrons
• What are atomic orbitals?

  a region around the nucleus that can hold up to two electrons with opposite spins
• What is the shape of s- orbitals - draw the graph

  electron cloud is in shape of a sphere

  
• How many orbitals and so electrons are in s-, p- and d-sub-shells?

  s - 1 orbital, 2 electrons

  p - 3 orbitals, 6 electrons

  d - 5 orbitals, 10 electrons
• What is the shape of p orbitals?

  dumb-bell shaped electron cloud

  3 separate p orbitals at right angles to each other

  
• How are the orbitals with the same energy filled?

  one in each orbital before pairing
• How are shorthand electron configurations written?

  use previous noble gas in format [noble gas] and all sub-shells in it are accounted for
• How is the periodic table divided into blocks?

  s block - group 1 and 2

  p block - group 3 to 8

  d block - centre - between group 2 and 3
• What is ionic bonding?

  the electrostatic attraction between positive and negative ions
• What is the structure of ionic compounds?

  giant ionic lattice
• Describe and explain the melting and boiling points of ionic compounds

  High melting and boiling points

  A lot of energy required to break strong ionic bonds - strong forces of electrostatic attraction between ions

  The melting points are higher for lattices with greater ionic charges - stronger attraction between ions
• Describe and explain the solubility of ionic compounds

  Dissolve in polar solvents e.g water

  Polar water molecules break down the lattice and surround each ion in solution

  greater ionic charge means there is stronger electrostatic attraction between ions so less soluble
• Describe and explain the electrical conductivity of ionic compounds

  Does not conduct when solid

  Ions in fixed position so no mobile charge carriers

  Does conduct when aqueous or molten (liquid)

  solid ionic lattice breaks down so ions free to move as mobile charge carriers
• What are the properties of ionic compounds?

  high melting and boiling points

  dissolve in polar solvents

  conduct electricity when aqueous or liquid
• What is covalent bonding?

  the strong electrostatic attraction between a shared pair of electrons and oppositely charged nuclei
• What happens to orbitals in covalent bonding?

  orbitals overlap
• What is a dative covalent bond?

  shared pair has been supplied by only one bonding atom

  e.g formation NH4 from NH3 + H+

  represented by arrowhead
• What is average bond enthalpy?

  measurement for covalent bond strength larger value = stronger bond
• What is electron repulsion theory?

  electron pair repel so arranged far apart as possible

  this minimises repulsion so holds bonded atoms in definite shape
• How do lone pairs effect bonded pairs?

  stronger repulsion so repel bonded pairs closer together

  for each lone pair bond angle reduced by 2.5 degrees
• What is a tetrahedral shape?

  bonded pairs - 4 pairs

  lone pairs - 0 pairs

  bond angle - 109.5 degrees

  shape -

  
• What is a pyramidal shape?

  bonded pairs - 3 pairs

  lone pairs - 1 pairs

  bond angle - 107 degrees

  shape -

  
• What is a non-linear shape?

  bonded pairs - 2 pairs

  lone pairs - 2 pairs

  bond angle - 104.5 degrees

  shape -

  
• What is a linear shape?

  bonded pairs - 4 pairs 2 regions

  lone pairs - 0 pairs

  bond angle - 180 degrees

  shape -

  
• What is a trigonal planar shape?

  bonded pairs - 3 pairs

  lone pairs - 0 pairs

  bond angle - 120 degrees

  shape -

  
• What is a octahedral shape?

  bonded pairs - 6 pairs

  lone pairs - 0 pairs

  bond angle - 90 degrees

  shape -

  
• What is electronegativity?

  the attraction of a bonded atom for the pair of electrons in a covalent bond
• What factors effect electronegativity?

  increases across and up the periodic table

  nuclear charge increases - nucleus has greater charge and so force of electrostatic attraction to valence electrons

  atomic radius decreases - nucleus stronger force of electrostatic attraction to valence electrons as closer
• How can you deduce what bond based on electronegativity difference?

  covalent - 0

  polar covalent - 0 - 1.8

  ionic - greater than 1.8
• What is a non-polar bond?

  bonded electron pair is shared equally between atoms
• How do you know when a bond is non-polar?

  when bonded atoms are the same

  bonded atoms have the same or similar electronegativity
• What is a polar bond?

  the bonded electron pair is shared unequally between bonded atoms
• How do you know when a bond is polar?

  when bonded atoms are different and have different electronegativity values
• What is a dipole?

  pair of opposite charges separated
• What type of dipole do polar covalent bonds have?

  permanent dipole
• What are intermolecular forces?

  weak interactions between dipoles of different molecules
• What are the types and relative strengths of intermolecular forces?

  induced dipole-dipole interactions - London forces (weakest)

  permanent dipole-dipole interactions (stronger)

  hydrogen bonding (strongest)
• How are dipoles induced (London forces)?

  instantaneous dipole forms in molecule - more electrons at one side of molecule causes this

  more electrons in side molecule repel those in molecule next to it so they move to one side - inducing a dipole

  induced dipole further induces dipoles on neighbouring molecules

  they then attract one another

  temporary

  
• What factors effect London forces?

  more electrons = stronger London forces

  larger instantaneous and induced dipoles

  greater induced dipole-dipole interactions

  stronger attractive forces between molecules

  more energy needed to overcome stronger force
• When are permanent dipole-dipole interactions present?

  between polar molecules