Topic 13

Question 1

Ionic bonding

Answer 1

the bigger the charge on an ion the stronger the electrostatic attraction between ions
More energy is needed to overcome these forces so they have melting/boiling points.
KCL is made up of K+ and Cl- - 770C
and CaO is made up of Ca2+ and O2- and has a melting point 2572C

Question 2

Born-Haber cycles

Answer 2

start with solid lithium chloride.

Question 3

theoretical and experimental Lattice enthalpies

Answer 3

lattice enthalpy values tell us how purely ionic

A perfect ionic model
1. ions that are perfectly spherical
2. the charge is evenly distrubuted in this shpere

the more polarisation we get, the more covalent character there will be

ionic compound with larger charges such as magenesium chloride (2+) have a larger distortion, larger polarisation, (larger change in lattice enthalpy)- so have more covalent character than ionic compounds with a +1 charge.

Lithium chloride is the most ‘perfectly ionic’ in this data as it has the lowest percentage in lattice enthalpy.

Question 4

polarisation

Answer 4

smaller cations are more polarising than larger ones

smaller cations have a higher charge density as the charge is concentrated in a smaller area. the cation pulls electrons towards itself more readily.
larger anions with a large charge are polarised much more easily than smaller, lowered charged anions
this is because the electrons are further away from the mculeus and there is more repulsion between the electrons in the ion. the lectrons can be pulled way towards the cations.

Question 5

electronegativity

Answer 5

electronegativity is the ability for an atom to attract electrons towards itself in a covalent bond
the furtehr right you go the more electronegative. Fluroine is the most electronegative

Question 6

Enthalpy change of hydration

Answer 6

charge- ions with a higher charge attract water molecules more strongly as the electrostatic attraction is stronger. more energy is released when the bond is made which means they have more exothermic enthalpy of hydration.
the larger the charge the greater the enthalpy of hydration.
Size
smaller ions have a higher charge density than larger ions. they can attract water molecules more strongly hence there is more exothermic enthalpy of hydration. the smaller the ion the greater the ethalpy of hydration

Question 7

Entropy

Answer 7

entropy is the measure of disorder in a system.
Entropy is given S.
the more disorder there is the higher the level of entropy.
Solids are aranged in a regular structure so have low entropy (low disorder). gases are the opposite
the number of particles also affects entropy change. if a reaction is the same state but more moles are produced then entropy increases. there are more ways energy can be distrubuted.
dinitrogen tetroxide producting nitrogen dioxide shows increasing entropy. (more moles of gas produced)
N2O (g) –> 2NO2(g)