IB HL chemistry: 2.10-20; all bonding HL topics

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12 Terms

1
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Explain résonance structures

When a molecule has multiple valid VSEPR structures, those are resonance structures

  • the actual structure is intermediate between the pair.

  • It’s called a resonance hybrid

  • Bond length/order and bond density is an average of the two structures

  • There must be at least a PI bond present, as that the delocalised electron which goes from one bond to the other.

  • Occurs when there are adjacent atoms of equivalent electro negativity

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Evidence for resonance structure of benzene

  • all bond angles and lengths are the same

  • Enthalpy of hydrogenation is lower than expected ( only 210 instead of 360). More stable bc of pi bonds

  • Saturation tests; it didn’t react as alkene would react; didn’t turn bromide water colourless as. Doesn’t undergo addition reaction with bromide p, but substitution

3
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Expanded octets

  • only smaller atoms, period 3 or above

  • The energy level of 3p and 3d is very similar

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Higher VSEPR

Fuck VSEPR - use drawn flash cards or kognity

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Formal charge formula

Number of valence electrons - number of lone electrons - nr of electrons in bonding pairs

  • The closer to 0 the more stable

  • Can happen with coordination bond

  • For an ion net formal charge has to be same as overall chance and for a molecule it has to be 0

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Sigma bond

Head on overlap of orbitals; ie s-s, p-p, s-p.

Single bonds are Always sigma

Stronger than pi, as there is only one electron dense region on the inter nuclear axis

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Pi bond

  • sideways overlap of p orbitals

  • Different Axial plane than sigma bonds as the electrons repel each other

  • These are all the extra bonds after a single bond

  • They are weaker than sigma bonds and are first to break, as they are located further away from the positive charge of the nucleus

  • If there are multiple Pi orbitals close to each other, the electrons are delocalised and can move through there

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Excitation of electron

Moving from ground state to excited state by energy absorption

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Hybridisation

  • mix of atomic orbitals to produce hybrid orbitals of intermediate energy; ie between S and between P

  • total energy hasn’t changed -, but has been equally redistributed

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carbon SP3 hybridisation

one electron from S orbital and 3 from P blend together

only single bonds as no P orbitals left

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carbon SP2 hybridisation

one electron from S orbital and 2 from P blend together

double bonds can be formed as a P is left

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carbon SP hybridisation

one electron from S orbital and one from P blend together

triple bonds can be formed as there still are 2 P orbitals left