Formation of Ionic compounds Born Haber cycles Formation of Ionic compounds

Formation of MX (Cation = +1, Anion = -1) Write a balanced equation for the formation M(s) + ½ X2(g)  MX(s) (eg Na(s) + ½ Cl2(g)  NaCl(s) if NaCl) What bond is present in this compound? Ionic Bond What ions are present in this compound? M+ and X- (eg Na+ and Cl- if NaCl) How is the bond formed? Attraction between M+ and X- as they move together M + X - ie M+(g) + X-(g)  MX(s)

What has to happen while MX forms? M(s) + ½ X2(g)  MX(s) and M +(g) + X -(g)  MX(s) What processes occur during the formation of MX? M(s)  M(g) ½ X2(g) X(g) M(g)  M+(g) + e- X(g) + e-  X-(g) M +(g) + X -(g)  MX(s) Which of these are exothermic and which are endothemic? What are the names of these processes? Endo (have to break metallic bond) Endo (have to break covalent bond Endo (have to overcome attraction between nucleus and electrons) Exo (electrons attracted to the nucleus) Exo (ions attract) A , B: Atomisation ( H(at) : The enthalpy change associated with the formation of one mole of gaseous atoms C : 1st Ionisation energy: The amount of energy required to remove one of electrons from one mole of gaseous atoms D : 1st Electron Affinity: The amount of energy given out when one mole of gaseous atoms gains one mole of electrons E : Lattice energy: The enthalpy change associated with the formation of one mole of an ionic lattice from its gaseous ions

Formation of MX (Cation = +2, Anion = -2) Write a balanced equation for the formation M(s) + ½ X2(g)  MX(s) (eg Mg(s) + ½ O2(g)  MgO(s) if MgO) What bond is present in this compound? Ionic Bond What ions are present in this compound? M+2 and X-2 (eg Mg+2 and O-2 if MgO) How is the bond formed? Attraction between M+2 and X-2 as they move together M +2 X -2 ie M+2(g) + X-2(g)  MX(s)

What has to happen while MX forms? M(s) + ½ X2(g)  MX(s) and M +2(g) + X -2(g)  MX(s) What processes occur during the formation of MX? M(s)  M(g) ½ X2(g) X(g) M(g)  M+(g) + e- M+(g)  M+2 + e- X(g) + e-  X-(g) X-(g) + e-  X-2(g) M +2(g) + X -2(g)  MX(s) Which of these are exothermic and which are endothemic? What are the names of these processes? Endo (have to break metallic bond) Endo (have to break covalent bond Endo (have to overcome attraction between nucleus and electrons) Exo (electrons attracted to the nucleus) Endo (electrons are repelled by the negative charge) Exo (ions attract) A , B: Atomisation ( H(at) : The enthalpy change associated with the formation of one mole of gaseous atoms C : 1st Ionisation energy: The amount of energy required to remove one of electrons from one mole of gaseous atoms D : 2nd Ionisation energy: The amount of energy required to remove one of electrons from one mole of gaseous ions E : 1st Electron Affinity: The amount of energy given out when one mole of gaseous atoms gains one mole of electrons F :2nd Electron Affinity: The amount of energy required for one mole of gaseous atoms to gain one mole of electrons G : Lattice energy: The enthalpy change associated with the formation of one mole of an ionic lattice from its gaseous ions

Formation of MX2 (Cation = +2, Anion = -1) Write a balanced equation for the formation M(s) + X2(g)  MX2(s) (eg Mg(s) + F2(g)  MgF2(s) if MgF2) What bond is present in this compound? Ionic Bond What ions are present in this compound? M+2 and X- (eg Mg+2 and F- if MgF2) How is the bond formed? Attraction between M+2 and X- as they move together X - M +2 X - ie M+2(g) + 2X-(g)  MX2(s)

What has to happen while MX forms? M(s) + X2(g)  MX(s) and M +2(g)+ 2X - (g)  MX2 (s) What processes occur during the formation of MX? M(s)  M(g) X2(g) 2X(g) M(g)  M+(g) + e- M+(g)  M+2 + e- 2X(g) + 2e-  2X-(g) M +2(g) + 2X -(g)  MX2(s) Which of these are exothermic and which are endothemic? What are the names of these processes? Endo (have to break metallic bond) Endo (have to break covalent bond Endo (have to overcome attraction between nucleus and electrons) Exo (electrons attracted to the nucleus) Exo (ions attract) A : Atomisation ( H(at) : The enthalpy change associated with the formation of one mole of gaseous atoms B : Atomisation (2 x H(at) : The enthalpy change associated with the formation of one mole of gaseous atoms C : 1st Ionisation energy: The amount of energy required to remove one of electrons from one mole of gaseous atoms D : 2nd Ionisation energy: The amount of energy required to remove one of electrons from one mole of gaseous ions E : 2 x 1st Electron Affinity: The amount of energy given out when one mole of gaseous atoms gains one mole of electrons G : Lattice energy: The enthalpy change associated with the formation of one mole of an ionic lattice from its gaseous ions

Formation of M2X (Cation = +1, Anion = -2) Write a balanced equation for the formation 2M(s) + ½X2(g)  M2X(s) (eg 2Na(s) + ½O2(g)  Na2O(s) if Na2O) What bond is present in this compound? Ionic Bond What ions are present in this compound? M+2 and X- (eg Na+ and O-2 if Na2O) How is the bond formed? Attraction between M+ and X-2 as they move together M + X - M + ie 2M+ (g) + X-2(g)  M2O (s)

What has to happen while M2X forms? 2M(s) + ½ X2(g)  M2X(s) and 2M + (g) + X -2 (g)  M2X (s) What processes occur during the formation of MX? 2M(s)  2M(g) X2(g) 2X(g) 2M(g)  2M+(g) + 2e- X(g) + e-  X-(g) 2X(g) + 2e-  2X-(g) 2M +(g) + X -2(g)  M2X(s) Which of these are exothermic and which are endothemic? What are the names of these processes? Endo (have to break metallic bond) Endo (have to break covalent bond Endo (have to overcome attraction between nucleus and e- Exo (electrons attracted to the nucleus) Endo (have to overcome repulsion between negative ion and e- Exo (ions attract) A : Atomisation ( 2 H(at) : The enthalpy change associated with the formation of one mole of gaseous atoms B : Atomisation ( H(at) : The enthalpy change associated with the formation of one mole of gaseous atoms C :2x 1st Ionisation energy: The amount of energy required to remove one of electrons from one mole of gaseous atoms E : 1st Electron Affinity: The amount of energy given out when one mole of gaseous atoms gains one mole of electrons F : 2nd Electron Affinity: The amount of energy required for one mole of gaseous atoms to gain one mole of electrons G : Lattice energy: The enthalpy change associated with the formation of one mole of an ionic lattice from its gaseous ions

Draw Born Haber cycle MX (+/-)

Draw Born Haber cycle MX (+2/-2)

Draw Born Haber cycle MX2 (+2/-1)

Draw Born Haber cycle M2X (+1/-2)

Solubility Definitions Enthalpy of Solution: Eg NaCl(s)  Na+(aq) + Cl-(aq) CuSO4(s)  Cu2+(aq) + SO4-2(aq) MgCl2(s)  Mg2+(aq) + 2Cl-(aq) Hydration Energy: Na+(g)  Na+(aq) Cl-(g)  Cl-(aq) Cu2+(g)  Cu2+(aq) SO4-2(g)  SO4-2(aq) Mg2+(g)  Mg2+(aq) 2Cl-(g)  2Cl-(aq) (2HHE Cl-) The enthalpy change associated with the dissolving of ONE MOLE of an IONIC compound in water The enthalpy change associated with hydration of ONE mole of Gaseous ions There are 6 molecules of water around each ion What makes an ion have a Highly Exothermic Hydration Energy? SMALL and HIGHLY CHARGED

What happens when a solid dissolves? If NaCl(s)  Na+(aq) + Cl-(aq) Then the following has to happen NaCl(s)  Na+(g) + Cl-(g) The lattice has to be broken up (supply the LE) Na+(g) + Cl-(g)  Na+(aq) + Cl-(aq) The ions are hydrated (Hydration energy is given out) Hence we can set up a Hess Cycle Hsoln NaCl HHE(Na) + HLENaCl HHE(Cl) HENCE HLENaCl + Hsoln NaCl = HHE(Na) + HHE(Cl)

What happens when a solid dissolves? If MgCl2(s)  Mg+2(aq) + 2Cl-(aq) Then the following has to happen MgCl2(s)  Mg+2(g) + 2Cl-(g) The lattice has to be broken up (supply the LE) Mg+2(g) + 2Cl-(g)  Mg+2(aq) + 2Cl-(aq) The ions are hydrated (Hydration energy is given out) Hence we can set up a Hess Cycle Hsoln MgCl 2 HHE(Mg) HLEMgCl 2HHE(Cl) 2 + HENCE HLEMgCl + Hsoln MgCl = HHE(Mg) + 2HHE(Cl) 2 2

Problems with Born Haber Cycle Assumes TRUE IONIC BONDING No Polarisation occurs This is only true for ionic compounds formed between: LARGE CATION LOWLY CHARGED CATION SMALL ANIONS

Polarised Ionic Small Highly charged cation (Nucleus of cation is not shielded greatly) Large anion Outer shell of anion is shielded from its’ nucleus RESULT: Outer shell of anion is attracted towards the nucleus of the cation Distorts (polarises) the shape of the anion

Polarised ionic 9 - 3 + LiF: F Outershell electrons pulled towards F nucleus- so NO Distortion 9 - 9 - 3 + LiI: I Outershell electrons pulled towards Li nucleus- so Distortion occurs (Polarised Ionic)