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2016 topic 4.1 bonding - ionic

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IB Chemistry Bonding Topic 4

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2016 topic 4.1 bonding - ionic

  1. 1. LECTURE 1 Ionic Bonding IB Chemistry Power Points Topic 4 Bonding www.pedagogics.ca
  2. 2. STRUCTURE AND BONDING
  3. 3. TYPES OF BONDING CHEMICAL BONDS.... are strong intramolecular bonds that hold atoms together in molecules, ionic solids and metals. These bonds are broken and made in chemical reactions. ionic covalent dative covalent (or co-ordinate) metallic PHYSICAL BONDS.... are intermolecular forces that exist between two or more separate molecules. These are the attractions involved in physical changes. van der Waals‘ forces - weakest dipole-dipole interactions hydrogen bonds - strongest
  4. 4. PART 1: CHEMICAL BONDS
  5. 5. THE IONIC BOND Ionic bonds are formed between elements whose atoms tend to “lose” electrons to gain the nearest noble gas electron 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¯
  6. 6. THE IONIC BOND Ionic bonds are formed between elements whose atoms tend to “lose” electrons to gain the nearest noble gas electron 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¯ oxidation reduction
  7. 7. THE IONIC BOND Ionic bonds are formed between elements whose atoms tend to “lose” electrons to gain the nearest noble gas electron 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¯ oxidation reduction 2,8,1 2,8 2,8,7 2,8,8
  8. 8. THE IONIC BOND Ionic bonds are formed between elements whose atoms tend to “lose” electrons to gain the nearest noble gas electron 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¯ oxidation reduction 2,8,1 2,8 2,8,7 2,8,8 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 3p 5 1s 2 2s 2 2p 6 3s 2 3p 6
  9. 9. SODIUM CHLORIDE – LIVE BOND FORMATION Cl SODIUM ATOM 2,8,1 Na CHLORINE ATOM 2,8,7
  10. 10. SODIUM ION 2,8 CHLORIDE ION 2,8,8 both species now have ‘full’ outer shells; ie they have the electronic configuration of a noble gas Oppositely charged ions are held together by electrostatic forces in a repeating pattern called a crystal lattice structure Na + Cl
  11. 11. ELECTRON TRANSFER Mg ——> Mg 2+ + 2e¯ and 2Cl + 2e¯ ——> 2 Cl¯ Mg Cl Cl e¯ e¯ FORMATION OF MAGNESIUM CHLORIDE
  12. 12. MAGNESIUM CHLORIDE - LIVE Cl MAGNESIUM ATOM 2,8,2 Mg CHLORINE ATOMS 2,8,7 Cl
  13. 13. Cl MAGNESIUM ION 2,8 Mg CHLORIDE IONS 2,8,8 Cl 2+
  14. 14. • 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 Recall: 1st IONISATION ENERGY (1 st I.E.) The energy required to remove one mole of electrons (to infinity) from the one mole 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) Successive IE’s (2 nd , 3 rd , etc) get larger as the proton:electron ratio increases. Large jumps in value occur when electrons are removed from shells nearer the nucleus because there is less shielding and more energy is required to overcome the attraction. If the I.E. values are very high, covalent bonding will be favoured (e.g. beryllium). THE FORMATION OF POSITIVE IONS - review
  15. 15. • 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 AFFINITY The energy change when one mole of gaseous atoms acquires one mole of electrons (from infinity) to form one mole of gaseous negative ion e.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 an electron is attracted. THE FORMATION OF NEGATIVE IONS - review
  16. 16. Octet Rule - Ions form from a tendency toward a lower energy, stable, noble gas electron configuration Transition metals have more complex electron arrangements thus can form more than one ion.
  17. 17. IONIC COMPOUNDS - CRYSTAL LATTICE STRUCTURE Cl- Chloride ion Na + Sodium ion Oppositely charged ions held in a regular 3-dimensional lattice by electrostatic attraction The arrangement of ions in a crystal lattice depends on the relative sizes of the ions 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. 18. Each Na + is surrounded by 6 Cl¯ and each Cl¯ is surrounded by 6 Na + Oppositely charged ions held in a regular 3-dimensional lattice by electrostatic attraction: The arrangement of ions in a crystal lattice depends on the relative sizes of the ions
  19. 19. Physical properties of ionic compounds Melting point very high A large amount of energy must be put in to overcome the strong electrostatic attractions and separate the ions. Strength Very 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. 20. IONIC COMPOUNDS - ELECTRICAL PROPERTIES SOLID IONIC COMPOUNDS DO NOT CONDUCT ELECTRICITY Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - IONS ARE HELD STRONGLY TOGETHER + IONS CAN’T MOVE - IONS CAN’T MOVE MOLTEN IONIC COMPOUNDS DO CONDUCT ELECTRICITY Na + Cl - Na + Cl - Na + Cl - Na + Cl - IONS HAVE MORE FREEDOM IN A LIQUID SO CAN MOVE TO THE ELECTRODES SOLUTIONS OF IONIC COMPOUNDS IN WATER DO CONDUCT ELECTRICITY DISSOLVING AN IONIC COMPOUND IN WATER BREAKS UP THE STRUCTURE SO IONS ARE FREE TO MOVE TO THE ELECTRODES
  21. 21. Many ionic compounds are soluble in water - dissolving

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