2.2.2 Bonding and structure
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define ionic bonding
• ionic bonding is the electrostatic force of attraction between oppositely charged ions in all directions
describe the involvement of outer shell electrons in ionic bonding
• outer shell electrons of metallic atoms are transferred to non-metallic atoms, forming oppositely charged ions
what are some properties of ionic compounds
• solid at room temp • high mp • conduct electricity when molten or aqueous but not when solid as ions are free to move and carry charge • soluble in polar solvents
why do ionic compounds have high mp
• lots of energy required to break the strong electrostatic force of attraction between oppositely charged ions in all directions
what is a giant ionic lattice
regular structure made of the same basic unit repeated over again > formed because ions are electrostatically attracted in all directions to ions of opposite charged
what 2 factors affect the mp/bp of ionic compounds
• ionic charge: greater charge, stronger electrostatic force, higher mp • ionic radius: smaller ionic radius, stronger electrostatic force, higher mp
what happens to the ionic radii down the group
• increases down the group • more electron shells • ion gets bigger • lower mp
what happens to ionic radii of isoelectronic ions
• if any ions have same electron configuration > the ion that is most positive is the smallest > there are more protons so greater attraction to e- and holds them tighter so higher mp
how are ionic compounds able to dissolve in polar substances
• polar substances e.g. water molecules break down an ionic lattice by surrounding each ion to form a solution > slight charges within polar substances attract charged ions in giant ionic lattice
why does the greater the ionic charge have reduced solubility
• ionic attraction too strong for water to break down lattice
what is covalent bonding
• the strong electrostatic force of attraction between a shared pair of electrons and the nuclei of bonded atoms
what is the involvement of outer shell electrons in covalent bonding
• outer shell electrons are shared between atoms
a covalent bond can also be described as the overlap…
• overlap of atomic orbitals, each containing one electron to give a shared pair of electrons
what does it mean that the attraction in a covalent bond is localised
• the attraction acts solely between shared pair of electrons and nuclei of the bonded atoms > this can result in a small unit called a molecule
what is a molecule
• the smallest part of a covalent compound that can exist whilst retaining the chemical properties of the compound
how many covalent bonds do the following form: Carbon, Nitrogen, Oxygen, Hydrogen
• Carbon - 4 • Nitrogen - 3 • Oxygen - 2 • Hydrogen - 1
what is a dative covalent (coordinate) bond
• a covalent bond where the shared pair of electrons has been supplied by one of the bonding atoms only > the shared pair was originally a lone pair of electrons on one of the bonded atoms > represented as an arrow in displayed formula
what is metallic bonding
• the electrostatic force of attraction between metal cations and delocalised electrons
what is the involvement of outer shell electrons in metallic bonding
• outer shell electrons of metallic atoms are lost to form metal cations and a sea of delocalised electrons
what is average bond enthalpy
• a measure of the average energy of a covalent bond > larger value of average bond enthalpy, stronger the covalent bond
what are the two types of covalent structures
• simple molecular lattice • giant covalent lattice
describe the bonds + forces within simple molecular structures
• atoms within each molecule are held by strong covalent bonds • different molecules are held by weak intermolecular forces e.g. london forces
what are the properties of simple molecules
• low mp/bp - weak imf • non-conductors - no charged particles • soluble in non-polar solvents
what are the properties of giant covalent stuctures
• high mp/bp - strong covalent bonds • insoluble in polar + non-polar - covalent bonds too strong to be broken