Understanding Ionic and Covalent Compounds in Chemistry

1. Ionic and Covalent Compounds… • Write down the Electronic Configurations and Box Notations for: • Ca • Mg2+ • Cu • V(IV) • CO2

2. Ionic Compounds… An IONIC BOND is the electrostatic attraction between a positive and negative ion that is formed by the transfer of (at least) one electron from the metal to the non-metal.

3. Ionic Compounds… Metals are ALWAYS positive Non-metals are ALWAYS negative (complex ions are the only exception)

4. Ionic Compounds… • Dot and Cross diagrams show where electrons have been transferred to and from. They obey the following guidelines: • Use square brackets • Only show the outer shell of e- • The charge must be shown

5. Ionic Compounds… Potassium metal forming an ion + K K

6. Ionic Compounds… Chlorine forming an ion - x x x x Cl Cl x x x x x x x x x x

7. Potassium reacting with Chlorine + K K - x x x x Cl Cl x x x x x x x x x x

8. Ionic Lattices… • Ionic compounds form lattices where: • Each +ve ion is surrounded by –ve ions • Each –ve ion is surrounded by +ve ions • Electrostatic attractions are experienced from all angles • You can calculate the number of ions from the mass of the crystal

9. Ionic Lattices…

10. Ionic Lattices… • All lattices have the following properties: • High melting/boiling point • Electrical conductivity • Solubility • In pairs, explain why.

11. Ionic Lattices… • Melting/Boiling Points • There are STRONG ELECTROSTATIC bonds between each ion • These require HIGH amounts of ENERGY to break • This energy is provided in the form of HIGH TEMPERATURES

12. Ionic Lattices… Melting/Boiling Points The larger the charge of the ions the higher the melting point of the compound. e.g. NaCl:mp = 801oC MgO:mp = 2,852oC

13. Ionic Lattices… Melting/Boiling Points If there is a difference in size of the ions the melting point decreases e.g. MgO:mp = 2,852oC SrO: mp= 2,531oC BaO: mp= 1,923oC

14. Ionic Lattices… Conductivity Solids DO NOT conduct electricity as the ions are in fixed positions. Liquids/solutions DO conduct electricity as the ions can MOVE and CARRY CHARGE

15. Ionic Lattices… Solubility Ionic solids will only dissolve in POLAR solvents. Water molecules have polar bonds The water molecules are attracted to the charged ions and break down the lattice They surround each ion causing it to dissolve

16. Ionic Lattices… Solubility

17. Identifying Compounds… • We’ve already learned how to identify the metal cation in a compound. Now we need to look at the tests for: • Non-metal cations • Anions

18. Identifying Compounds… Ammonium Add NaOH and warm gently Place red litmus paper into the gas Positive Result: Red litmus turns blue Equation: NH4+(aq) + OH-(aq)  NH3(aq) + H2O(l)

19. Identifying Compounds… When identifying compounds we must perform the tests in a specific order. Carbonates Sulphates Halides

20. Identifying Compounds… Carbonates Add a dilute strong acid Test any gas evolved with limewater Positive Result: Fizzing then limewater goes cloudy Equation: CO32-(aq) + 2H+(aq)  CO2(g) + H2O(l)

21. Identifying Compounds… Sulphates Add a dilute hydrochloric acid Add aqueous BaCl2 Positive Result: White Precipitate formed Equation: SO42-(aq) + Ba2+(aq)  BaSO4(s)

22. Identifying Compounds… Halides Dissolve in water Add aqueous silver nitrate Positive Result: Precipitate formed Equation: Ag+(aq) + X-(aq)  AgX(s)

23. Identifying Compounds… • Halides • To determine the identity of the halide we first look at the colour: • White ppt = Chloride • Cream ppt = Bromide • Yellow ppt = Iodide

24. Identifying Compounds… • Halides • If we cannot tell the colour (happens often) we add the ammonia • Dissolves in dilute= Chloride • Dissolved in conc = Bromide • Insoluble = Iodide

25. Covalent Compounds… A COVALENT BOND is a shared pair of electronsthat are electrostatically attracted to the positive nuclei of both atoms taking part in the bond.

26. Covalent Compounds… • Dot and Cross diagrams show where electrons have been transferred to and from. They obey the following guidelines: • No square brackets • Only show the outer shell of e- • Pair of electrons must be clearly shown

27. Covalent Compounds… Bromine Br x x Br Br x x x x x x x Br x x x x x

28. Covalent Compounds… DATIVE bonds are formed when the Octet Rule is not satisfied. They often lead to a charged compound such as ammonium.

29. Covalent Compounds… Ammonium + H H N H x x x H

30. Covalent Compounds… Ammonium + H H N H H

31. Covalent Compounds… Bond Strength Bond strengths are given as positive values because breaking bonds is an ENDOTHERMIC process. The LARGER the value the STRONGER the bond

32. Covalent Compounds… The Octet Rule is useful for the most part but there are certain elements that can be satisfied with less/more than eight electrons in their largest Quantum Number.

33. Covalent Compounds…

34. Covalent Compounds… Boron trifluoride x x x x B F F x x x x x x x x x x x F x x x x x x

35. Covalent Compounds… Phosphorus pentafluoride x x x x F x F x x x x x x x x x x x P x x F x F x x x x x x F x x x x x x x x x x

36. Covalent Compounds… • Simple Molecules • Strong covalent bonds form between atoms • Weak intermolecular forces between molecules • Limited number of atoms

37. Covalent Compounds… • Giant Lattice • Strong covalent bonds between all atoms • No intermolecular forces to consider (except Graphite) • Potentially infinite number of atoms

38. Covalent Compounds… Properties

39. Covalent Compounds… Graphite forms layers of carbon atoms bonded to 3 other carbons. Intermolecular forces hold the layers together. One of the valence electrons is not involved in bonding. Therefore it is free to move (delocalised) and carry a charge.