TOPIC 2: Bonding and Structure Flashcards
(25 cards)
Ionic compounds bond
Oppositely charged ions held together by electrostatic attractions
Molecular ions:
Hydroxide
Nitrate
Ammonium
Sulfate
Carbonate
OH -
NO3 -
NH4 +
SO4 2-
CO3 2-
Characteristics of ionic compounds (5)
- Giant ionic regular, cubic, patterned structure.
- Dissolve in water, polar.
- Conduct electricity when molten or dissolved, free ions.
- High melting points, strong electrostatic forces.
- Brittle, layers slide and repel.
Effects of (charge density):
Size of charge
Size of ion
- Bigger charge, stronger attraction.
- Smaller ion, closer so stronger attraction.
Melting point increases with charge density.
Isoelectric Ions
Different atoms with same number of electrons.
Radius decreases as atomic number increases.
Covalent Bonding
Electrostatic attraction between the shared electrons and positive nucleus.
Dative covalent bond
One atom donates 2 electrons to an atom/ion to form bond
Bond enthalpy and bond length
Greater electron density -> shorter -> higher enthalpy.
Repulsive forces between nuclei and electrons balance with attractive= length.
Shapes of molecules repulsion
Minimise electron repulsion.
Lone pair repulsion > bonded pair repulsion.
Single bond = double bond
Shapes of molecules - no lone pairs.
2 Linear 180
3 Trigonal Planar 120
4 Tetrahedral 109,5
5 Trigonal Bipyramidal 90, 120
6 Octahedral 90
Shapes of molecules - lone pairs
3, 1 Non linear 119
4, 1 Trigonal pyramidal 107
4, 2 Non linear 104.5
5, 1 Seesaw 102, 87
5, 2 Distorted T 87.5
6, 1 Square pyramidal 81.9, 90
6, 2 Square planar 90
Graphite- giant covalent structure (4)
Carbons bond 3 times so 4th electron delocalised, conduct electricity.
Strong bonds so high melting point and insoluble.
Weak forces between layers, slide.
Layers far apart compared to covalent bond length, low density.
Diamond- giant covalent structure (3) similar to…
Carbon bonds 4 times so tetrahedral.
Strong bonds so high melting point and insoluble.
Tightly packed so conducts heat.
SiO2
Graphene- giant covalent structures (3)
1 atom thick hexagonal rings so lightweight and transparent.
Delocalised electrons so conduct electricity and strengthen covalent bonds.
Eg: aircrafts
Metallic bonding
Electrostatic attraction between positive metal ions and negative sea of delocalised electrons.
Metal properties- giant metallic lattice. (3)
Strong bonds so insoluble and high melting points, more electrons atom can donate, higher point.
Delocalised electrons so good electrical and thermal conductors.
Malleable and ductile, ion layers can slide and still attract.
Electronegativity
Ability for an atom to attract electrons towards itself in a covalent bond.
The bigger the difference the more ionic character.
Polar molecule
Polar bonds and unsymmetrical
London intermolecular forces
Instantaneous (temporary) dipole-induced dipole when molecules/atoms are near. (Electron clouds)
The weakest force, decreases with branching, increases with size so does boiling point.
On all molecules.
Dipole-dipole intermolecular forces.
Weak electrostatic forces due to permanent polarities (dipole molecules).
Hydrogen bonding intermolecular forces. 2 examples
Hydrogen bonds with the lone pair on N, O or F.
Strongest force as involves the most electronegative forces.
Has all three bonding types.
Examples: ice forms regular structure so less dense than water and alcohols are less volatile than alkanes.
Solubility
- Solvent breaks, substance breaks and thus new bonds form
- New bonds must be = or > than broken.
Polar solvents (water).
Polar (ionic) dissolve = hydration.
Non ionic (alcohols) dissolve if hydrogen bond but the bigger hydrocarbon the less soluble.
Polar (haloalkanes) don’t dissolve as weak dipoles, only via dipole dipole, water will hydrogen bond itself.
Non-polar solvents.
For non-polar molecules (alkanes) to form London forces.
Water will hydrogen bond itself.
