2.1- ionic model Flashcards
cations
when metal atoms lose electrons, positive ions
anions
when non metal atoms gain electrons they form negative ions
ionic bonding
electrostatic attraction between oppositely charged ions
ionic compounds
exist as 3D lattice structures
ammonium
NH4+
hydroxide
OH-
Nitrate
NO3-
Hydrogencarbonate
HCO3-
carbonate
CO3 2-
sulfate
SO4 2-
Phosphate
PO4 3-
binary ionic compounds
compunds with two elements
named with cation first followed by anion
anion adopts the suffix “ide” eg magnesium sulfide or sodium oxide
lattice enthalpy
measure of the strength of the ionic bond in different compounds
why will atoms bond together
to achieve a decrease in their potential energy, lower energetic state is more stable, in practice this is achieved by atoms gaining a full outer shell
3 major types of electronic interaction are possible, resulting in 3 different bonding, what type occurs depends on electronegativity difference of atoms interacting
ionic
low electronegativity atoms (metals) interacting with high electronegativity atoms (non-metals)
electronegativity difference bigger than 1.7 units
covalent
both atoms have middle to high electronegativity (both non-metals)
electornegativity difference less than 1.7 units
metalic
both atoms have low electronegativity (both metals)
ionic compounds structure and properties
giant ionic
-solid insulator
-melt/ dissolve conduct
-brittle
-high melting point
-hard some are soluble
covalent compounds structure and properties
simple covalent
giant covalent macromolecules
simple covalent:
weak intermolecular forces, low melting points, weak, brittle, non- conducters
giant covalent:
high melting point, non conducter (except graphite), insoluble
describe how ionic bonding takes place
metal loses electrons to form a positive ion (cation), oxidation
non metal will gain electrons to form a negative ion (anion), reduction
in both cases atoms achieve the same electronic configuration as nobel gases. This is called ISOELECTRONIC
oxidation formula
M -> Mn+ + ne-
n= a number
reduction formula
X + ne- -> Xn-
what happens once the ions are formed (process of ionic bonding)
electrostatic force of attraction between oppositely charged ions causes them to pack together into a 3d Giant ionic lattice with every cation surrounded by anions and vis versa
the electrostatic attraction, between ions is the ionic bond
describe size of cation and anion
as cation has been formed through loss of outermost energy level the cations are smaller than metal atoms
as anion has formed by the gain of electrons they are bigger than the neutral atom, due to increase in electron electron repulsion and expansion of the outer energy level, in general the cation is smaller than the anion
transition metals have
variable oxidation states and hence can have variable charges
conduction in ionic susbtances
conduct electricity when molten or in a solution, as ions are free to move around and can pass to the elctrodes dipped in solution to become oxidised or reduced (electrolysis)
melting point ionic substances
high, as large number of ionic bonds must be broken to allow the ions to move around or break free from the attractive forces completely (ionic gas)
ions held together by strong electrostatic forces of attraction
softness or hardness and maleability or brittle ionic susbtances
hard and brittle, ionci lattice does not bend, once sufficinet force is applied the structure gives away completely and material snaps
strong electrostatic attraction between oppositely charged ions
solubility ionic substances
more soluble in polar solvnts that have an uneven charge distribution (such as water) than non polar solvents (eg. hexane). The ions become surrounded by the polar solvent molecules and are dissolve (hydrated in case of water)
polar water molecules surround the ions and free them into solution, seperates between hydrated negative and positive ions
what is the strength of an ionic lattice measured by
lattice enthalpy, which is the energy recquired to break up a mole of an ionic lattice into gaseous ions under standar conditions
define lattice enthalpy
enthalpy change when one mole of solid ionic compound is seperated into its gaseous ions, this wold give the enthalpy change as endothermic (positive)
magnitude of the lattice enthalpy is a measure of
stability of the ionic lattice,
what two factors affect the stability of the ionic lattice
the size of ions- the smaller ions the more closely the ions can pack together and attract each other
the charge on the ions- the more charged is the ion the stronger is the elctrostatic force of attraction between them
lattice enthalpy formula
charge on cation X charge on anion/ sum of ionic radii
what is lattice enthalpy porpotional to and inversely porportional to
porportional- charge on cation X charge on anion
inversely- sum of ionic radii
