chemical bonding and structure Flashcards
valency definition
number of electrons that must be gained, shared or lost in order for an atom to achieve a noble gas configuration
definition of ionic bonding
the electrostatic force of attraction between 2 oppositely charged ions
definition of covalent bonding
electrostatic force of attraction between a shared pair of electrons and the positive nuclei of 2 atoms
definition of metallic bonding
electrostatic force of attraction between positively charged ions and a “sea” of delocalised electrons
structure of ionic compounds
giant ionic (crystal) lattice structure
structure of covalent compounds
simple covalent, giant covalent, macromolecules
difference between simple covalent, giant covalent and macromolecules
simple covalent: simple molecules with a countable number of atoms in a fixed ratio
giant covalent: uncountable number of atoms
macromolecules: covalent molecules joined together into chains of larger molecules
structure of metals
giant metallic lattice structure
why do metals have delocalised electrons
due to metals being packed closely in a regular arrangement, metal atoms ‘lose’ their valence electrons and become positively charged ions. the electrons no longer ‘belong’ to any metal atom and can freely move around the metal ions
similarities between ionic bonding, covalent bonding and metallic bonding
(strong) electrostatic forces of attraction, involve oppositely charged particles, can result in giant structures
hardness of different molecular structures
giant ionic crystal lattice: hard and brittle
simple covalent molecular structure: soft
giant covalent structure: hard (except graphite)
macromolecular structure: varies
giant metallic crystal lattice: malleable and ductile
why are giant ionic crystal lattice structures hard
the strong electrostatic forces of attraction between the oppositely charged ions causes them to resist motion and be resistant to deformation
why are giant ionic crystal lattice structures brittle
when a strong enough force is applied, ions move away from their lattice positions and are displaced. when ions of the same charge from adjacent layers face each other, the strong repulsive forces causes the lattice structure to cleave evenly
why are simple covalent structures soft
only a small amount of force is needed to overcome the weak intermolecular forces of attraction between the molecules
why are giant covalent structures hard
a large amount of force is needed to break the numerous strong covalent bonds between the atoms present in the structure
why is graphite soft unlike other giant covalent structures
layers of carbon atoms in graphite are held loosely by weak intermolecular forces of attraction and little force is required to overcome them, allowing them to slide over one another
why are giant metallic structures malleable and ductile
the ‘sea’ of delocalised electrons in the lattice do not belong to any particular metal ion so if sufficient force is applied to the metal, layers of ions can slide over one another without disrupting the bonding
malleable meaning
ability of a material to be hammered or pressed into shape without breaking or cracking
ductile meaning
ability of a material to be drawn into a thin wire
solubility of different structures in aqueous solvents
giant ionic crystal lattice: soluble except insoluble salts
simple covalent: insoluble except iodine, sugar, hcl, ammonia, carbon dioxide
giant covalent: insoluble
giant metallic lattice: insoluble
why are ionic lattice structures soluble in aqueous solvents
“like dissolves like” polar substances dissolve in polar solvents
solubility of different structures in organic solvents
giant ionic lattice: insoluble
simple covalent: soluble
giant covalent: insoluble
giant metallic lattice: insoluble
why are simple covalent structures soluble in organic solvents
“like dissolves like”, non-polar substances dissolve in non-polar solvents
electrical conductivity of different structures
giant ionic lattice: only in molten and aqueous states
simple covalent: poor in all states unless dissolved in water to form solutions with ions that can conduct electricity
giant covalent: poor except graphite
giant metallic lattice: good in solid and molten states
why can giant ionic lattice structures conduct electricity in molten and aqueous states
thereare mobile ions that can conduct electricity as the ionic compund can dissociate in water to form ions (aqueous) or the large amount of energy can overcome the strong electrostatic forces of attraction between oppositely charged ions (molten). aka the ions are no longer held in fixed positions and can move around and conduct electricity
in solid state, ions are held in fixed positions by electrostatic forces of attraction and cannot move.
why are simple covalent structures poor electrical conductors
there are no mobile ions and electrons / mobile charge carriers to conduct electricity
why are giant covalent structures poor electrical conductors
there are no mobile ions and electrons / mobile charge carriers to conduct electricity
why is graphite a good electrical conductor
graphite is comprised of carbon atoms with 4 valence electrons. each carbon atom only bonds to 3 others, leaving one unbonded valence electron per atom that is mobile within the layer to conduct electricity
why can giant metallic lattice structures conduct electricity in solid and molten states
there will be mobile electrons that can move around and conduct electricity
melting and boiling points of different structures
giant ionic lattice: high
simple covalent: low
giant covalent: high
giant metallic lattice: high
why do giant ionic lattice structures have high melting and boiling points
a large amount of energy is required to overcome the strong electrostatic forces of attraction between oppositely-charged ions
why do simple covalent structures have a low melting and boiling point
only a small amount of energy is required to overcome the weak intermolecular forces of attraction between molecules
why do giant covalent molecules have a high melting and boiling point
a large amount of energy is required to overcome the strong covalent bonds between atoms
why do giant metallic lattice structures have a high melting and boiling point
a large amount of energy is required to overcome the strong electrostatic forces between the positive ions and sea of delocalised electrons
why do alloys have lower melting and boiling points than pure metals
the presence of other elements in the alloy acts as impurities which lowers melting point. the different sizes of atoms in an alloy also make the lattice arrangement less regular than a pure metal, making bonds between atoms weaker and also lowering melting point
why can alloys conduct electricity
the presence of a ‘sea’ of delocalised electrons act as mobile charge carriers that allow the alloy to conduct electricity
why are alloys not very malleable and ductile
the different sizes of atoms disrupt the regular lattice arrangement of pure metals, hence layers of atoms cannot slide over each other easily
