4 Chemical Bonding & Structure Flashcards
electron domain: no. of electron domains, name of shapes, bond angles(s) [hint: theory shapes]
2 electron domains = linear = 180°
3 electron domains = trigonal planar = 120°
4 electron domains = tetrahedral = 109.5°
5 electron domains = trigonal bipyramidal = 90°, 120°, 180°
6 electron domains = octahedral = 90°, 180°
molecular geometry shapes [hint: possible shapes]
2 electron domains = linear = 180°
3 electron domains (3 bonded pairs) = trigonal planar = 120°
3 electron domains (2 bonded pairs) = bent/v-shaped = 90° < θ < 109.5°
4 electron domains (4 bonded pairs) = tetrahedral = 109.5°
4 electron domains (3 bonded pairs) = trigonal pyramidal = 107°
4 electron domains (2 bonded pairs) = bent/v-shaped = 90° < θ 109.5°
5 electron domains (5 bonded pairs) = trigonal bipyramidal = 90°, 120°, 180°
5 electron domains (4 bonded pairs) = distorted tetrahedral = bond angle unknown (not tested i think)
6 electron domains (6 bonded pairs) = octahedral = 90°, 180°
6 electron domains (4 bonded pairs) = square planar = 90° – square planar’s two unbonded pairs of electrons must be on opposite sides, below and above plane
what are resonance structures ?
certain molecules have more than one possible structure – structures are known as resonance hybrids, which are extreme forms of the true structure, which lies somewhere in between said resonance hybrids.
allotropes of carbon (C) [3]
and
their structure, bond strength, electrical conductivity
all allotropes of carbon are giant covalent structures
diamond: each C atom bonded to 4 other C atoms, forming giant covalent structure,, bonds are equally strong with no planes of weakness, hence diamond is exceptionally hard,, electrons are localized in tetrahedral formation, hence it does not conduct electricity
graphite: each C atom bonded to 3 other C atoms, forming giant covalent structure of layers of hexagonal rings,, bonds are weak between layers, which can slide over each other,, electrons are delocalized between layers, hence can conduct electricity
fullerene, C60: each C atom bonded to 3 other C atoms, arranged in hexagons and pentagons to give geodesic spherical structure (football shape) [not important to know other details]
note that bonds between carbon atoms are extremely strong, and that the weak bond for graphite refers to bonding between hexagonal layers
types of intermolecular forces [3]
and
determining presence, relative strength
london dispersion forces: electrons at any instantaneous moment may be unevenly spread producing temporary dipoles. this may induce another temporary dipole in another dipole, resulting in weak attraction,, london forces increases as mass increases
dipole-dipole forces: polar molecules attracted via electrostatic forces. polarity depends on electronegativity differences and its vector shape. polarity is present when there is resultant dipole,, weak but stronger than london,,
hydrogen bonding: occurs when hydrogen is bonded directly to an electronegative element (F, N, O),, electron pair is drawn away from H atom to electronegative element, and remaining in proton in H atom ‘attacks’ electronegative element’s non-bonding pair of electrons, resulting in stronger dipole-dipole attraction,, strongest force out of all 3
physical properties relation to bonding types [3]
melting & boiling points: london dispersion forces < dipole-dipole < hydrogen bonding / simple covalent < ionic < giant covalent – the stronger the attraction, the greater the m/b.p.
solubility: polar substances dissolve in polar solvents, non-polar substances dissolve in non-polar substances – solubility depends on polarity of substance and solvent. i.e. like substances and solvents dissolve. – organic molecules are good solvents as they have polar and non-polar ends of their chains (eg. ethanol dissolves both polar and non-polar substances)
conductivity: metals and graphite contain delocalized electrons and are excellent conductors. molten ionic compounds conduct electricity due to mobile ions. – delocalized electrons and mobile ions conduct electricity. substances without these are unable to conduct electricity
types of bonds and their formations of molecular orbitals [2]
sigma (σ) bonds: formed when two atomic orbitals on different atoms overlap head-on (either two s-orbitals, one s- and one p-orbital, or two p-orbitals)
pi (π) bonds: formed when two p-orbitals overlap sideways-on
- imagine a line drawn through the nucleus, where head-on refers to entering from the head-tail of line, whereas sideways-on refers to entering from sides of imaginary line [page 32 of study guide, diagram of formation is important]
formula of formal charge and what it is used for
formal charge used to determine preferred lewis structure of any compound for which two or more structures are available – preferred structure would be one where the sum of formal charges of all atoms is closest to zero
formula for formal charge of each individual atom = (no. of valence electrons) - (no. of non-bonded electrons) = 1/2 (number of bonded electrons)
more electronegative atoms and positive formal charges on the less electronegative atoms
ozone destruction reactions [2]
chlorofluorocarbons (CFC) produce chlorine radicals from high energy ultraviolet light in stratosphere causing homolytic fission of C-Cl bond:
CCl₂F₂ (g) –> CClF₂* (g) + Cl* (g) – radical initiation
ClO* (g) + O* (g) –> Cl* (g) + O₂ (g) or
Cl* (g) + O₃ (g) –> ClO* (g) + O₂ (g) – propagation of radicals
nitrogen oxides also catalytically decompose ozone:
NO₂ (g) –> NO (g) + O* (g)
O* (g) + O₃ (g) –> 2O₂ (g)
nitrogen oxide also regenerates destructive catalyst:
NO (g) + O₃ (g) –> NO₂ (g) + O₂ (g)
overall reaction for nitrogen oxide:
2O₃ (g) [NO₂ (g) –>] 3O₂ (g) – breakdown of ozone into oxygen
ozone destruction reactions [2]
chlorofluorocarbons (CFC) produce chlorine radicals from high energy ultraviolet light in stratosphere causing homolytic fission of C-Cl bond:
CCl₂F₂ (g) –> CClF₂* (g) + Cl* (g) – radical initiation
ClO* (g) + O* (g) –> Cl* (g) + O₂ (g) or
Cl* (g) + O₃ (g) –> ClO* (g) + O₂ (g) – propagation of radicals
nitrogen oxides also catalytically decompose ozone:
NO₂ (g) –> NO (g) + O* (g)
O* (g) + O₃ (g) –> 2O₂ (g)
nitrogen oxide also regenerates destructive catalyst:
NO (g) + O₃ (g) –> NO₂ (g) + O₂ (g)
overall reaction for nitrogen oxide:
2O₃ (g) [NO₂ (g) –>] 3O₂ (g) – breakdown of ozone into oxygen
