Ch19. Lattice energy Flashcards
Define Lattice energy
The enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions under standard conditions
Is lattice energy exothermic or endothermic? and also give the reason
- Exothermic
- Because when ions are combined to form an ionic solid lattice there is an extremely large release of energy
What does large n egative value of lattice energy suggests?
- That the ionic compound is much more stable than its gaseous ions
Define enthalpy change of atomisation
The standard enthalpy change of atomisation is the enthalpy change when 1 mole of gaseous atoms is formed from its element under standard conditions
Is enthalpy change of atomisation exothermic or endothermic? and also give the reason
It is always endothermic as energy is always required to break any bonds between the atoms in the element, to break the element into its gaseous atom
Define first electron affinity
The enthalpy change when 1 mole of electrons is added to 1 mole of gaseous atoms, to form 1 mole of gaseous ions each with a single negative charge under standard conditions
What are the factors that are affecting electron affinity?
- It depends on how strongly the incoming electron is attracted to the nucleus
- The greater the attractive forces between the electron and nucleus, the more energy is released and therefore, EA1 value will be more exothermic.
1. Nuclear charge: the greater the nuclear chage, the stronger the attractive forces between an incoming electron and the nucleus
2. Distance: the geater the distance between the nucleus and the outermost shell where the electron is added, the weaker the force of attraction - Shielding: the greater the number of shells, the greater the shielding effect and the weaker the force of attraction.
Describe the trends in the electron affinities of the Group 16 and Group 17 elements
- Electron affinities of non-metals become more exothermic across a period, with a maximum at Group 17.
- There is generally a downwards trend in the size of the electron affinities of the elements in Group 16 and 17.
- Electron affinities generally become less exothermic for each successive element going down both groups
Explain the trend of electron affinities in Group 16 and 17
Gointg down group 16-17
- The outermost electrons are held less tightly to the nucleus as they are further away
- The number of electron shells increases causing an increased shielding of the outermost electrons
- It gets more difficult to add an electron to the outer shell
- Less energy is released upon adding an electron to the outer shell
- so the EA1 becomes less exothermic
What is the effect to lattice energy as the ionic radius of ions increases? and explain the reason
- It becomes less exothermic
- This is because the charge on the ions is more spread out over the ion when the ions are larger
What is the effect to lattice energy as the ionic charge increases? and explain the reason
- It gets more exothermic
- The greater the ionic charge, the higher the charge density
- This results in stronger electrostatic attraction between the oppositely charged ions in the lattice.
Define standard enthalpy change of solution
The enthalpy change when 1 mole of an ionic substances dissolves in sufficient water to form a very dilute solution
Define standard enthalpy change of hydration
The enthaly change when 1 mole of a specified gaseous ion dissolves in sufficient water to form a very dilute solution
How does ionic radius affect enthalpy change of hydration?
- Enthalpy change of hydration becomes more exothermic with decreasing ionic radii
- smaller ions have a greater charge density resulting in stronger ion-dipole attractions between the water molecules and the ions in the solutions
How does ionic charge affect enthalpy change of hydration?
- Enthalpy change of hydration is more exothermic for ions with larger ionis charges
