H2 Chemistry: Lewis Structures

CO₂

linear, 180

BF₃

trigonal planar, 120

NH₃

trigonal pyramid, 107

• N has 1 lone pair, stronger repulsion than the 3 bond pairs

Explain VESPR theory.

Shape of molecule / ion determined by repulsions between e^-

1. e^- pairs around central atom will arrange themselves as far apart from each other as possible to minimise repulsion

2. Repulsion between LP & LP > LP & BP > BP & BP: LP is attracted to 1 nucleus, BP is attracted to 2 nuclei, so LP electron cloud is less elongated, take up more space around the nucleus, wider angle

BF₃NH₃

BF₃: trigonal planar, 120

NH₃: trigonal pyramid, 107

• BF₃ is electron-deficient, accepts lone pair from N in empty 2p orbital (dative bond)

H₂O

bent, 104.5

• 2 lone pairs + no neutralisation by 2 electron deficient H atoms

H₂S

bent, <104.5

• BP repulsion weaker as S is located further from central atom than O

• weaker repulsion, smaller bond angle between BP

CH₄

tetrahedral, 109.5

SO₄^2-

tetrahedral, 109.5

• Since S is in Period 3, expansion of octet: use energetically accessible 3d orbitals to form > 4 bonds

NO₃^-

trigonal planar, 120

• resonance structure as N & O both cannot exceed octet (Period 2)

O₃

bent, 118

• Since O is in Period 2, cannot expand octet as 3d orbitals are not energetically accessible

• dative bond between O atoms

NH₄⁺

tetrahedral, 109.5

• lone pair of N forms dative bond with 1 H⁺

• N more electronegative, likely to give away electrons

PCl₅

trigonal bypyramid, 90, 120

SF₄

see-saw, <90

• LP > BP

ClF₃

T-shape, 90

• 2 lone pairs

IF₂^-

linear, 180 (3LP, 2BP)

• dative bond from F to I (I only has 7 electrons in valence shell)

XeF₂

linear, 180

• Xe is a noble gas: 8 electrons in valence shell

SF₆

octahedral, 90

ClF₅

square pyramidal, ~90

ICl₄^-

square planar, 90