Perfect ionic model.

Slides:

Advertisements

Similar presentations

A2 – CHEMICAL ENERGETICS

Advertisements

Chemical Bonding Compounds are formed from chemically bound atoms or ions. Bonding involves only the valence electrons.

CI 4.5 Energy changes in solutions Why do some ionic substances dissolve in water, whilst others are insoluble? If there is enough energy to separate.

BORN-HABER CYCLES A guide for A level students KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS.

Topic c Bond energies and Enthalpies

15.2 Born-Haber Cycle Define and apply the terms lattice enthalpy, and electron affinity Explain how the relative sizes and the charges of.

Enthalpy Change of formation is the enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions. Enthalpy.

1Åm = 1×10 −10 m. The ångström is often used in natural sciences and technology to express the sizes of atoms, molecules, and microscopic biological structures,

YR 11 DP CHEMISTRY ROB SLIDER 15 ENERGETICS (AHL).

Title: Lesson 6 Born-Haber Cycles and Lattice Enthalpies Learning Objectives: – Understand the term lattice enthalpy – Use Born-Haber cycles to calculate.

CI 4.5 Energy changes in solutions Why do some ionic substances dissolve in water, whilst others are insoluble? If there is enough energy to separate.

Formation of Binary Ionic Compounds Binary Ionic Compound n Binary- two n Ionic- ions n Compound- joined together.

Ionic Compounds An ionic compound is composed of positive and negative ions that are combined so that the numbers of positive and negative charges.

Chapter 7 Ionic Bonding 7.1 Ionic Bonds: Donating and Accepting Electrons 7.2 Energetics of Formation of Ionic Compounds 7.3 Stoichiometry of Ionic.

Ionic Bonding. Formation of Bond Electrons are transferred from an atom of low electronegativity to one of high electronegativity Anion (-) and cation.

Example Calculate the reticular energy for LiF, knowing: Li (s) + ½ F 2(g) LiF (s) ΔH° kJ Applying Born Haber’s cycle, the formation of LiF is.

For an ionic compound the lattice enthalpy is the heat energy released when one mole of solid in its standard state is formed from its ions in the gaseous.

Born-Haber cycles, and lattice energy

CI 4.6 – Born-Haber Cycle (C) JHUDSON For an ionic compound the lattice enthalpy is the enthalpy change when one mole of solid in its standard state.

Lattice Energy & the Born-Haber Cycle g.recall the stages involved in the formation of a solid ionic crystal from its elements and that this leads to a.

A method to calculate Lattice Enthalpies

Formation of Ionic compounds

1 For an ionic compound the lattice enthalpy is the heat energy released when one mole of solid in its standard state is formed from its ions in the gaseous.

Ionic Bonding and Ionic Compounds

Discussing the difference between theoretically and experimentally derived lattice energies

Energy AS Revision: Energy terms Enthalpy change of reaction.ΔH r Enthalpy change of formation ΔH f Enthalpy change of combustion ΔH c Standard conditions.

Topic 15 Energetics (HL) 15.1 Standard enthalpy changes of reaction

Metallic bonding and structure L.O.:  Describe metallic bonding as the attraction of positive ions to delocalised electrons.  Describe giant metallic.

Title: Lesson 7 Lattice Enthalpies and Enthalpy Change of Solution

ENERGETICS IB Topics 5 & 15 PART 3 :Energy Cycles.

Born-Haber cycles L.O.:  Define and apply the terms enthalpy of formation, ionisation enthalpy, enthalpy of atomisation of an element and of a compound,

New Way Chemistry for Hong Kong A-Level Book 11 Intermediate Type of Bonding 9.1Incomplete Electron Transfer in Ionic Compounds 9.2Electronegativity of.

Born-Haber Cycle Section 15.2 (AHL). Lattice Enthalpy Of an ionic crystal: the heat energy absorbed (at constant pressure) when 1 mol of solid ionic compound.

Energetics IB Topics 5 & 15 PART 3: Energy Cycles.

12 Thermodynamics 12.1 Types of Enthalpy Change 12.2 Born-Haber Cycles 12.3 Enthalpy Changes – Enthalpy of Solution 12.4 Mean Bond Enthalpy 12.5 Entropy.

Mg(s) + C l 2 (g) MgC l 2 (s) Mg(g) + C l 2 (g) Mg(g) + 2C l (g) Mg 2+ (g) + 2C l – (g) 7 Mg + (g) + 2C l (g) Mg 2+ (g) + 2C l (g) Enthalpy.

New Way Chemistry for Hong Kong A-Level Book 11 Chapter 6 Energetics.

 When an ionic solid dissolves in water, two processes occur  Firstly the ions are separated (endothermic)  Secondly the ions are surrounded by water.

9 - 1 The Octet Rule Except for hydrogen and helium, atoms are most energetically stable if they have a completely filled valence shell. A completely filled.

Basic Concepts of Chemical Bonding

IB1 Chemistry HL Energetics Why do chemical reactions happen?

Energetics HL only 15.1 Standard Enthalpy Changes Standard Enthalpy of Formation,  H Ϧ f The enthalpy change when 1 mole of a compound is produced from.

Review Vocabulary Solvent Solute Solution Sublimation Diatomic Molecules Breaking bonds: energy change Creating bonds: energy change Periodic Trends for.

Ch. 13: Bonding Formation of Binary Ionic Compound.

ENERGETICS /THERMOCHEMISTRY (AS). 1.Often chemical changes are accompanied by changes in heat content / enthalpy of the materials reacting (H) 2. This.

2Na(s) + Cl 2 (g)  2NaCl (s) Synthesizing an Ionic Compound.

TOPIC 15 ENERGETICS/THERMOCHEMISTRY 15.1 ENERGY CYCLES.

Lattice enthalpy Textbook reference: p Born-Haber cycles L.O.:  Explain and use the term: lattice enthalpy.  Use the lattice enthalpy of a simple.

Ionic structures L.O. To be able to describe the energy changes involved in forming ionic compounds.

For an ionic compound the lattice enthalpy is the heat

Lattice enthalpy For an ionic compound the lattice enthalpy is the heat energy released when one mole of solid in its standard state is formed from its.

15.1 Energy cycles Representative equations can be used for enthalpy/energy of hydration, ionization, atomization, electron affinity, lattice, covalent.

Ionic Bonding Lattice Energy

15.2 Born-Haber Cycle Define and apply the terms lattice enthalpy, and electron affinity Explain how the relative sizes and the charges.

15.2 Born-Haber Cycle Define and apply the terms lattice enthalpy, and electron affinity Explain how the relative sizes and the charges.

Born-Haber Cycle.

Thermodynamics Definitions Forming Ionic Compounds

A guide for A level students KNOCKHARDY PUBLISHING

A guide for A level students KNOCKHARDY PUBLISHING

Sponge Give the ionic compound for the following: K+ + O2- Sr2+ + Cl-

Topics 5 & 15 Chemical Thermodynamics

Lattice Energy, DUlattice

15.2 Born-Haber Cycle Define and apply the terms lattice enthalpy, and electron affinity Explain how the relative sizes and the charges.

IB Topics 5 & 15 PART 3: Energy Cycles

8.5 Energy Effects in Ionic Compounds

PROPERTIES OF IONIC COMPOUNDS

Chapter 9 Chemical Bonding I: Lewis Theory

Chemical Bonds Na nucleus Name

Presentation transcript:

Perfect ionic model

Lattice dissociation enthalpy Definition: The lattice dissociation enthalpy, ΔHϴL (diss) is the enthalpy change when 1 mole of an ionic solid is separated into its gaseous ions Example: Sodium chloride (NaCl) NaCl (s) → Na+ (g) + Cl- (g) ΔHϴL (diss) = + 787 kJ mol-1 Energy must be put in to break the strong ionic bonds in the lattice; therefore it is an endothermic process

Factors affecting ΔHϴL The two factors which affect the value of ΔHϴL (diss) are: 1) The size of the ions The halide ions increase in size in the order F-, Cl-, Br- and I- The distance between the positive ion and negative halide ion increases Therefore the electrostatic force of attraction between the ions is weaker and the ΔHϴL (diss) values decrease Compound ΔHϴL (kJ mol-1) NaF 918 NaCl 780

Factors affecting ΔHϴL 2) The charges on the ions The greater the charges on the ions, the stronger the electrostatic force of attraction between the ions Therefore more energy is required to separate the ions and the ΔHϴL (diss) value increases Compound ΔHϴL (kJ mol-1) NaF 918 MgO 3791 Na+ F- Mg2+ O2-

Born-Haber cycles Born-Haber cycles are used to calculate lattice enthalpies, ΔHϴL from experimental data (ΔHϴf, ΔHϴdiss, ΔHϴi, ΔHϴea and ΔHϴat) We can also calculate lattice enthalpies, ΔHϴL using a model called the perfect ionic model

Perfect ionic model Definition: The lattice dissociation enthalpy, ΔHϴL (diss) is the enthalpy change when 1 mole of an ionic solid is separated into its gaseous ions The perfect ionic model assumes: The ions are perfect spheres The ions are held together only by electrostatic forces (pure ionic bonding)

ΔHϴL Born-Haber (kJ mol-1) ΔHϴL Perfect ionic model (kJ mol-1) We can compare the ΔHϴL (diss) values from the Born- Haber cycle (calculated from experimental data) with those from the perfect ionic model (theoretical) Compound (Alkali halides) ΔHϴL Born-Haber (kJ mol-1) ΔHϴL Perfect ionic model (kJ mol-1) NaCl 787 769 NaBr 747 732 NaI 704 682 KCl 701 690 KBr 670 665 KI 629 632

Perfect ionic model For the alkali halides there is good agreement between the ΔHϴL (diss) values from the Born-Haber cycle and the perfect ionic model We can conclude the structure of alkali halides is just like the perfect ionic model (ions are perfect spheres and held together only by electrostatic forces) This provides evidence to support the model works

Perfect ionic model We can conclude the structure of alkali halides is just like the perfect ionic model (ions are perfect spheres and held together only by electrostatic forces) The type of bonding in alkali halides is ionic bonding

ΔHϴL Born-Haber (kJ mol-1) ΔHϴL Perfect ionic model (kJ mol-1) For the silver halides there is less agreement between the ΔHϴL (diss) values from the Born-Haber cycle and the perfect ionic model Compound (Silver halides) ΔHϴL Born-Haber (kJ mol-1) ΔHϴL Perfect ionic model (kJ mol-1) AgF 955 870 AgCl 915 864 AgBr 904 830 AgI 889 808

Ionic with some covalent character Perfect ionic model The ions are not perfect spheres and there is some covalent bonding between the ions The type of bonding in silver halides is ionic with covalent character The perfect ionic model does not take into account any covalent bonding present between the ions Ionic Ionic with some covalent character

Perfect ionic model The type of bonding in silver halides is ionic with some covalent character More energy would be required to separate the ionic solid into gaseous ions as the bonding is stronger This explains the higher values of ΔHϴL (diss) from the Born-Haber cycle compared to the perfect ionic model Silver halides ΔHϴL Born-Haber ΔHϴL Perfect ionic AgCl 915 864 AgBr 904 830 AgI 889 808

Silver halides The electron cloud of the negative ion can be (distorted) polarised by the positive ion Negative ions are easily polarised if they are large Iodide ions are large and are easily polarised and therefore the ionic bond has the greatest covalent character This explains why there is the greatest difference in ΔHϴL (diss) values between the B-H cycle and the perfect ionic model for silver iodides