Chemical Bonding Flashcards
Define covalent bond.
Covalent bond is the electrostatic forces of attraction between the shared electrons and the positively charged nuclei.
What are the requirements for dative bonding?
The donor atom must provide two electrons from a lone pair of electrons and the acceptor atoms must contain an empty valence orbital.
Define bond energy.
Bond energy is the amount of energy required to break one mole of covalent bonds in the gaseous state.
How does the strength of a covalent bond depend on the bond order?
As the bond order increases, the number of bonding electrons within the inter-nuclei region increases, increasing the electrostatic forces of attraction for these electrons increases.
How does effectiveness of orbital overlap affect the strength of covalent bond?
Larger orbitals are more diffused, resulting in less effective orbital overlap. Hence bonds formed by larger atoms have lower bond strength.
How does bond polarity affect the strength of covalent bond?
In a polar bond, there are additional attractive forces between the positive dipole and negative dipole that strengthen the covalent bond, leading to higher bond strength
Why is the bond energy of F-F lower than Cl-Cl despite Cl being a bigger atom?
As the F atom is very small, the F-F bond length is very short. This results in the non-bonding electrons on F being in close proximity with those of the other F atom. Hence, repulsion occurs which weakens the covalent bond. This happens in small molecules such as F2 and O2.
Name the two principles in the VSEPR theory
- Electron pairs around a central atom are arranged as far apart as possible so as to minimise repulsion.
- Lone pair-lone pair repulsion > lone pair-bond pair repulsion > bond pair-bond pair repulsion
Why does ethanoic acid have a Mr 120 which is twice of its expected Mr of 60?
This is due to each acid molecule pairing up to form a cyclic dimer via hydrogen bonds.
What affects the strength of instantaneous dipole-induced dipole interactions?
a) number of electrons. a molecule with more electrons will have a bigger and more polarisable electron cloud. This leads to stronger id-id interactions,
b) shape of molecule. compared to spherical molecules with similar Mr, elongated molecules will have greater surface of contact. This leads to stronger id-id interactions.
What affects the strength of permanent dipole-permanent dipole interactions?
The strength of pd-pd interactions increases as the dipole moment of the molecules increases. ie when the molecule becomes more polar
Define hydrogen bond.
A hydrogen bond is defined as the electrostatic forces of attraction between the partial positive hydrogen atom that is directly bonded to a very electronegative F, O and N atom and a lone pair of electrons of another F, O and N atom.
What affects the strength of hydrogen bonds?
The strength of hydrogen bonds increases when the electronegativity of the atom bonded to the hydrogen atom increases.
It also increases when the extensiveness of hydrogen bonding increases.
