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2012 topic 4.1 bonding - ionic

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  • 1. IB Chemistry Power Points Topic 4 Bondingwww.pedagogics.ca LECTURE 1 Ionic Bonding
  • 2. STRUCTURE AND BONDINGKey Concept:The physical properties of a substance (such as hardness, density, meltingpoint and conductivity) depend on the structure of the substance. Bondingdetermines arrangement of particles and therefore, the type of structure.Basic theory – things you should know1. The noble gases (He, Ne, Ar, Kr, Xe and Rn) are in Group VIII, they are all relatively inert meaning they do not react and bond like other elements.2. We can conclude that noble gas electron configuration appears to confer stability. All noble gases have just filled their ‗outer shell‘ of electrons3. Other elements have a tendency to obtain the same electron arrangement (a full outer shell of valence electrons). Obtaining this electron arrangement is accomplished by different methods of chemical bonding.4. The type of bonding depends on an element‘s position in the periodic table
  • 3. TYPES OF BONDINGCHEMICAL BONDS....are strong intramolecular bonds that hold atomstogether in molecules, ionic solids and metals. Thesebonds are broken and made in chemical reactions. ionic covalent dative covalent (or co-ordinate) metallicPHYSICAL BONDS....are intermolecular forces that exist between two ormore separate molecules. These are the attractionsinvolved in physical changes. van der Waals‗ forces - weakest dipole-dipole interactions hydrogen bonds - strongest
  • 4. PART 1: CHEMICAL BONDS
  • 5. THE IONIC BONDIonic bonds are formed between elements whose atoms tend to ―lose‖electrons to gain the nearest noble gas electronic configuration and thosewhich tend to ―gain‖ electrons. The electrons are transferred from one atom tothe other. Sodium Chloride + Na ——> Na + e¯ and Cl + e¯ ——> Cl¯
  • 6. THE IONIC BONDIonic bonds are formed between elements whose atoms tend to ―lose‖electrons to gain the nearest noble gas electronic configuration and thosewhich tend to ―gain‖ electrons. The electrons are transferred from one atom tothe other. Sodium Chloride + Na ——> Na + e¯ and Cl + e¯ ——> Cl¯ 2,8,1 2,8 2,8,7 2,8,8
  • 7. THE IONIC BONDIonic bonds are formed between elements whose atoms tend to ―lose‖electrons to gain the nearest noble gas electronic configuration and thosewhich tend to ―gain‖ electrons. The electrons are transferred from one atom tothe other. Sodium Chloride + Na ——> Na + e¯ and Cl + e¯ ——> Cl¯ 2,8,1 2,8 2,8,7 2,8,8 2 2 6 1 2 2 6 2 2 6 2 5 2 2 6 2 6or 1s 2s 2p 3s 1s 2s 2p 1s 2s 2p 3s 3p 1s 2s 2p 3s 3p HL only responsible for s,p,d,f electron configurations
  • 8. THE IONIC BOND Ionic bonds are formed between elements whose atoms tend to ―lose‖ electrons to gain the nearest noble gas electronic configuration and those which tend to ―gain‖ electrons. The electrons are transferred from one atom to the other. Sodium Chloride + Na ——> Na + e¯ and Cl + e¯ ——> Cl¯ 2,8,1 2,8 2,8,7 2,8,8 2 2 6 1 2 2 6 2 2 6 2 5 2 2 6 2 6 or 1s 2s 2p 3s 1s 2s 2p 1s 2s 2p 3s 3p 1s 2s 2p 3s 3pboth species end up with the electronic configuration of the nearest noble gasthe resulting ions are held together in a crystal lattice by electrostatic attraction.
  • 9. SODIUM CHLORIDE Na ClSODIUM ATOM CHLORINE ATOM 2,8,1 2,8,7
  • 10. SODIUM CHLORIDE + Na ClSODIUM ION CHLORIDE ION 2,8 2,8,8 both species now have ‘full’ outer shells; ie they have the electronic configuration of a noble gas
  • 11. THE IONIC BOND FORMATION OF MAGNESIUM CHLORIDE e¯ Cl ELECTRON Mg TRANSFER Cl e¯ 2+Mg ——> Mg + 2e¯ and 2Cl + 2e¯ ——> 2 Cl¯
  • 12. MAGNESIUM CHLORIDE Cl Mg CHLORINE ATOMS 2,8,7MAGNESIUM ATOM Cl 2,8,2
  • 13. MAGNESIUM CHLORIDE Cl 2+ Mg CHLORIDE IONS 2,8,8MAGNESIUM ION Cl 2,8
  • 14. THE FORMATION OF POSITIVE IONS• also known as cations; they are smaller than the original atom.• formed when electrons are removed from atoms.• the energy associated with the process is known as the ionisation energy stRecall: 1st IONISATION ENERGY (1 I.E.)The energy required to remove one mole of electrons (to infinity) from the onemole of gaseous atoms to form one mole of gaseous positive ions. + +e.g. Na(g) ——> Na (g) + e¯ or Mg(g) ——> Mg (g) + e¯Other points (HL topic 12) nd rdSuccessive IE‘s (2 , 3 , etc) get larger as the proton:electron ratio increases.Large jumps in value occur when electrons are removed from shells nearer thenucleus because there is less shielding and more energy is required toovercome the attraction.If the I.E. values are very high, covalent bonding will be favoured (e.g.beryllium).
  • 15. THE FORMATION OF NEGATIVE IONS• known as anions• are slightly larger than the neutral atom - electron repulsion in outer shell• formed when electrons are added to atoms• energy is released as the nucleus pulls in an electron• this energy is the electron affinity.ELECTRON AFFINITYThe energy change when one mole of gaseous atoms acquires one mole ofelectrons (from infinity) to form one mole of gaseous negative ione.g. Cl(g) + e¯ ——> Cl¯(g) and O(g) + e¯ ——> O¯(g)The greater the effective nuclear charge (E.N.C.)of a species, the easier anelectron is attracted.
  • 16. Ions form from a tendency toward a lower energy,stable, noble gas electron configurationTransition metals have more complex electron arrangements(d – subshell HL material) thus can form more than one ion.
  • 17. IONIC COMPOUNDS - CRYSTAL LATTICE STRUCTURE Oppositely charged ions held in a regular 3-dimensional lattice by electrostatic attractionThe arrangement of ions in a crystal lattice depends on the relative sizes of the ions Cl- Chloride ion + Na Sodium ion + The Na ion is small enough relative to a Cl¯ ion to fit in the spaces so that both ions occur in every plane.
  • 18. Oppositely charged ions held in a regular 3-dimensionallattice by electrostatic attraction:The arrangement of ions in a crystal lattice depends on the relative sizesof the ions + Each Na is surrounded by 6 Cl¯ + and each Cl¯ is surrounded by 6 Na
  • 19. Physical properties of ionic compoundsMelting pointvery high A large amount of energy must be put in to overcome the strong electrostatic attractions and separate the ions.StrengthVery brittle Any dislocation leads to the layers moving and similar ions being adjacent. The repulsion splits the crystal.Electrical don‘t conduct when solid - ions held strongly in the lattice conduct when molten or in aqueous solution - the ions become mobile and conduction takes place.Solubility Insoluble in non-polar solvents but soluble in water Water is a polar solvent and stabilises the separated ions.
  • 20. IONIC COMPOUNDS - ELECTRICAL PROPERTIES - - SOLID IONIC Cl Cl + + Na Na IONS ARE HELD STRONGLY TOGETHER COMPOUNDS DO - - Cl Cl + + Na + IONS CAN‘T MOVE NOT CONDUCT Na ELECTRICITY - - - IONS CAN‘T MOVE Cl Cl + + Na Na MOLTEN IONIC - IONS HAVE MORE FREEDOM IN A COMPOUNDS DO Na + Cl LIQUID SO CAN MOVE TO THE CONDUCT ELECTRODES ELECTRICITY - Na + Cl + - NaSOLUTIONS OF IONIC Cl DISSOLVING AN IONIC COMPOUND COMPOUNDS IN Na + IN WATER BREAKS UP THEWATER DO CONDUCT - STRUCTURE SO IONS ARE FREE TO Cl MOVE TO THE ELECTRODES ELECTRICITY
  • 21. Many ionic compounds are soluble in water - dissolving