IB Chemistry HL: the covalent model: 2.2.1-4

covalent bonds

The electrostatic force of attraction between two positive nuclei and a shared pair of electrons.

exceptions to Octet rule

PCl5 and SF6 - they have an expanded octets such as in molecules with d-orbitals that can accommodate more than eight electrons that have not been used in bonding

BeCl2 : Be can be stable with only 4 electrons: electron deficient

BCl3: B can be stable with only 6 electrons: electron deficient.

why is Fluorine’s bond enthalpy lower than expected

because of the non bonding electrons on the outer shells which repel each other and reduce the overall bond strength.

Sometimes short single bonds ( eg F-F and O-O) are weaker than expected due to repulsion between non-bonding electron pairs on these small atoms

hydroxonium ion

H3O+

is a positively charged ion formed when water molecules accept a proton (H+) from an acid. in that case, the oxygen donated both electrons needed to make the covalent bond.

Dative/coordination covalent bonds

both electrons from the covalent bond where donated by the same atom.

what counts as a “bonding pair” in VSPR shape reprediction

• all bonds to another atoms: so a double bond still counts as a bonding pair

Shape when 2 bonding pairs + no non-bonded pairs

Linear, 180°

shape when 3 bonding pairs

Trigonar planar, 120°

shape when 2 bonding pairs one non bonding pair

Bent/ V shaped

shape when 4 bonding pairs

Tetrahedral- 109.5°

shape when 3 bonding pairs one non bonding pair

Trigonal pyramidal - Greater repulsion by non bonding pair, so bond angle smaller than 109.5°

shape when 2 bonding pairs 2 non bonding pairs

Bent (water) , less than 105°, as a lot of repulsion from non bonding pairs

5 bonding pairs shape

trigonal pyramidal

6 bonding pairs shape

Octahedral

4 bonding pairs 1 non bonding pairs

Distorted tetrahedral

4 bonding pairs 2 non bonding pairs

square planar: non bonding pairs as far as possibe above and below the plane

Differences between single and double bond

the higher the number of bonds, the higher the bond strength and higher the bond length as there are more electrons attracted to the atoms nucleus