bonding Flashcards
define ionic bonding
the electrostatic attraction between positive and negative ions
name two examples of common cations
metal ions
ammonium ions
name two examples of common anions
non-metal ions
polyatomic ions
describe the structure of an ionic compound
each ion attracts oppositely charged ions in all directions, so the result is a giant ionic lattice structure containing billions of ions.
describe the properties of ionic compounds
- high melting and boiling points
- only conduct electricity when liquid or aqueous
- tend to dissolve in polar solvents such as water
explain why ionic compounds have high melting/boiling points
the electrostatic attraction between oppositely charged ions is strong and therefore requires a large amount of energy to overcome, which can only be provided by high temperatures
explain why ionic compounds only conduct electricity when liquid or aqueous
in a solid state the ions are in a fixed position and cannot move, so there are no mobile charge carriers
when liquid or aqueous the solid ionic lattice breaks down, meaning the ions are now free to move and carry charge
explain why ionic compounds tend to dissolve in polar solvents
the dipoles on the water molecules can bind to oppositely charged ions and break them apart
what does solubility depend on?
the relative strengths of the attractions within the giant ionic lattice and the attractions between ions and water molecules
define covalent bonding
the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
what is a dative covalent bond?
a covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only. the shared electron pair was originally a lone pair.
what is the difference between a single and a double covalent bond?
in a single covalent bond only one pair of electrons are shared (2), whereas in a double covalent bond two pairs of electrons are shared (4)
define metallic bonding
the strong electrostatic attraction between positive ions (cations) and delocalised electrons
how many electrons would be in a metallic bond with metals of a 2+ charge?
twice as many electrons as cations (each atom donated its outer shell electrons to the ‘shared pool’ of delocalised electrons)
what are the properties of metals?
high melting/boiling points
high electrical conductivity
strong metallic bonds
explain why most metals have high melting and boiling points
high temperatures are needed to provide the large amounts of energy required to overcome the strong electrostatic attraction between the cations and delocalised electrons
what does the melting/boiling point depend on?
the strength of the bonds holding together the atoms in the lattice
explain why metals have a high electrical conductivity in both solid and liquid states
they have delocalised electrons which can move throughout the structure and carry charge
name the three elements that form a giant covalent lattice
boron, carbon, silicon (and silicon dioxide)
what are the three allotropes of carbon?
diamond, graphite and graphene
what are the properties of diamond?
tetrahedral structure
high melting/boiling point
does not conduct electricity, as all four outer shell electrons in each atom are involved in covalent bonding with other atoms (this makes diamond very strong)
what are the properties of graphite?
high melting/boiling point
can conduct electricity
hexagonal layers bonded by weak London forces
what is the difference between graphite and graphene?
graphene is one layer of graphite
why can graphite/graphene conduct electricity?
only three electrons in the outer shell of each carbon atom are involved in covalent bonding, so the other electron is delocalised and can move, carrying charge
describe the variation of melting point across periods 2/3 in terms of structure and bonding
the melting point increases from group 1 to 4, and then sharply decreases between groups 4 and 5. This marks the change from giant to simple molecular structures. simple molecular structures have lower melting points as the bonds between them are weaker, requiring less energy to overcome.
what is a giant covalent lattice?
a network of atoms joined by strong covalent bonds
