Lattice Enthalpy

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Lattice Enthalpy

Born Haber cycles - Used to calculate the lattice energy.

Enthalpy Change Of Atomisation

The standard enthalpy change of atomisation is the enthalpy change when 1 mole of gaseous atoms is formed from its elements under standard conditions.

Ion Polarization

The ability of a cation to attract electrons and distort an anion is called the polarizing power of the cation.

It is the distortion of the electron cloud, where the anion is not spherical.

The anion is more likely to be polarized if

4. The anion has a charge of 2- or 3-

3. Anion is large

2. Cation has a charge of 2+ or 3+

1. Cation is small

The degree of polarization of anion depends on

2. The ease with which the anion can be polarized (Polarizabilty)

1. The charge density of the cation

Electron affinity

The second electron affinity is the enthalpy change when 1 mole of electron is added to 1 mole of gaseous 1- ions to form 1 mole of gaseous 2- ions under standard conditions

O-(g) + e- = O2-(g)

The first electron affinity is the enthalpy change when 1 mole of electrons is added to 1 mole of gaseous atoms to form 1 mole of gaseous 1- ions under standard conditions.

Cl(g) + e- = Cl-(g)

Lattice Energy

Change of lattice energy down the group

5. Decrease in the lattice energy is relatively small down the group.

4. As a sulfate ion is much larger than the group 2 cation, the sulfate ion contributes a relatively greater part to the change in the lattice energy down the group

3. The lattice energy is also inversely proportional to the sum of the radii of the anion and cation

2. The lattice energy decreases in the order Mg2+> Ca2+> Sr2+> Ba2+

1. Lattice energy is greater if the ions (with the same charge) forming the lattice are small

Factors affecting the Value of Lattice Energy

2. Charge of the ion - As the ionic charge increases, the lattice energy becomes more exothermic.

1.Ion size - As the size of the ion increases, the lattice energy becomes less exothermic (Applies to both anions and Cations). Ions with the same ionic charge have a lower charge density if their radius is larger. This occurs because the same charge is spread out over a larger volume.

Lattice - A rigid arrangement. Regular repeated arrangement of alternating ions in a crystal

Formula = K*(Q1*Q2)/r^2

Is the Enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions under standard conditions.