3: Ionic interactions

Question 1

what are the two major sources of energy in chemical reactions?

Answer 1

interactions between charged species (ions)
making / breaking of covalent bonds

Question 2

what practical testing method is used to determine lattice structure?

Answer 2

X-ray diffraction
locates position of nuclei and maps e- density

Question 3

ionic radii is…

Answer 3

more or less independent of the salt

Question 4

name the force between ions in a lattice

Answer 4

electrostatic / coulomb interaction

Question 5

electrostatic energy is proportional to… and inversely proportional to…

Answer 5

proportional to the charges involved (q1 and q2)
inversely to the distance r between the two charges

Question 6

the sign of the energy for a favourable interaction will be…

Answer 6

NEGATIVE, indicating a lowering of the energy due to favourable interaction

Question 7

describe the energy of interaction at the equilibrium distance

Answer 7

the distance at which the energy is at a minimum

Question 8

what is the Madelung constant, M?

Answer 8

when using a model to calculate the energy of the interactions of any one ion with those around it, the constants add up to the Madelung constant (approx 1.6-2.5, depending on the particular arrangement)

Question 9

what is the Born-Lande equation used to calculate?

Answer 9

the energy at equilibrium separation of ions (also, at a minimum)
or the energy of interactions between ions in a crystal lattice

Question 10

what does the Born-lande equation take into considerations apart from the electrostatic energy?

Answer 10

the repulsion between ions (which is inversely proportional to r^n)

Question 11

born-lande equation (simplified)

Answer 11

energy at equilibrium = - M N(Avogadro) x electrostatic energy (1 - 1/n)

Question 12

what is the value of M when calculating energy between an ion pair?

Answer 12

M = 1
bc only one single interaction between oppositely charged ions

Question 13

define lattice energy

Answer 13

energy needed to take ions from lattice into gas phase (no longer interacting)

Question 14

trends of ionic radii

Answer 14

increase going down group
anions > cations, generally

same period, 2+ ions < 1+, and 2- ions > 1-

Question 15

what do the kapustinskii equations express?

Answer 15

lattice energy
simplified: bc ratio M/v (v=# ions in formula) v similar, and take n=9

Question 16

what two factors are lattice energy dominated by?

Answer 16

charges on the ions
ionic radii
(so basically the same as what the electrostatic energy depends on)

Question 17

lattice energy will be large if…

Answer 17

charges on ions large (proportional)
size of ions small (inverse)

Question 18

oxidation states of fluoride vs other halides

Answer 18

fluorides of high ox states relatively easy to prepare
other halides difficult / impossible (tends to decompose to lower ox state with the release of the halogen)
bc this decomposition is exothermic for all halogens except fluorine

Question 19

lattice energy of fluorine vs other halogens

Answer 19

fluorine ion is unusually small compared to other halogens - relatively big increase in lattice energy

Question 20

trend for reactions of G1 metals with oxygen

Answer 20

oxide –> peroxide –> superoxide (O2^2- anion)
metals with larger ions tend to form the superoxide