Topic 14.1: Further aspects of covalent bonding and structure Flashcards
Exceptions to octet rule (Expanded)
Elements in Period 3 and below
Explanation of the exception to octet rule (expanded)
a) Available d orbitals in the valence shell have energy values relatively close to those of the p orbitals.
b) Promotion of electrons will allow additional electron pairs to form
Examples of molecules with expanded octet
a) PCl5
b) SF4
c) ClF3
d) I3-
e) SF6
f) BrF5
g) XeF4
Conditions of molecular polarity
a) If there are no lone pairs and all the atoms attached to the central atom are the same, the molecules are non-polar as there is no net dipole
b) If the atoms attached to the central atom are not all the same, there may or may not be a net dipole depending on the symmetry.
c) The presence of lone pairs often, but not always, results in a polar molecule
What happens to the electrons in a resonance structure?
Instead of being combined to one location, e- tend to be shared between more than one bonding position (delocalized)
What involves delocalization?
a) This involves electrons that are shared by/between more than one pair in a molecule or ion as opposed to being localized between a pair of atoms
b) There is a p orbital on each atom and these overlaps side-on to form the π delocalized system
Definition of formal charge
Charge an atom would have if all atoms in a molecule had the same electronegativity
Formula to calculate formal charges
FC=V - (0.5B + L)
What is the most stable structure according to formal charges?
a) Formal charge value closest to 0
b) The negative charges located on the most electronegative atom
How are covalent bonds formed?
Overlapping of half-filled orbitals, creating a bonding orbital between the two atoms.
How is a sigma bond formed?
By the direct head-on/end-to-end overlap of orbitals resulting in electron density concentrated between the nuclei of the bonding atoms
a) s - s (H2)
b) s - p (HCl)
c) p - p (Cl2)
d) HO - s (C - H in CH4)
e) HO - HO (C - C in C2H6)
Atomic orbitals which overlap in sigma bonds
a) s - s (H2)
b) s - p (HCl)
c) p - p end-on (Cl2)
d) HO - s (C - H in CH4)
e) HO - HO (C - C in C2H6)
How is a pi bond formed?
By the sideway overlap of orbitals resulting in electron density above and below the plane of the nuclei of the bonding atom
Atomic orbitals which overlap in pi bonds
p - p sideways (C - C in C2H4)
Hybridization of orbitals in:
a) Single
b) Double
c) Triple
a) 1 sigma
b) 1 sigma / 1 pi
c) 1 sigma / 2 pi
