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Ionic bonding, Lewis Dot Diagrams

Ionic bonding, Lewis Dot Diagrams. Gilbert Newton Lewis (surrounded by pairs of electrons). Recall: Valence electrons are the electrons in the outer orbit surrounding an atom in a Bohr-Rutherford Diagram. How to Remember??

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Ionic bonding, Lewis Dot Diagrams

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  1. Ionic bonding, Lewis Dot Diagrams Gilbert Newton Lewis (surrounded by pairs of electrons)

  2. Recall: Valence electrons are the electrons in the outer orbit surrounding an atom in a Bohr-Rutherford Diagram

  3. How to Remember?? • Find the group number the element is in while skipping the transition metals

  4. Lewis diagrams • Write the Symbol and draw dots around the outside representing the outer orbit (these will be the valence electrons) e.g. Ne = group 8, Sb = group 5, etc. F P Ne Sb Rb • The single electrons represent bonding sites • They all want to have 8 in their valence orbit (octet rule) therefore they either gain (5 or more) or lose (3 or less) .

  5. Ionic Compounds • Metal and a non-metal combine to form "Ionic Compounds". • The metal atoms loses electrons to form positive ions. • The non-metal gains the electrons to form negative ions. • The two ions join together • The result is an electrically neutral ionic compound. • Ion + Ion = Ionic Compound

  6. Ionic compounds are formed when a metal gives one or more of its electrons to a non metal. If we draw the Lewis Structure for the metal (Chemical Symbol with Valence Electrons), We can use an arrow to show the transfer of the electrons. When all of the electrons are gone, the metal’s inner orbit of electrons is full. So, the metal is stable. The atom has lost electrons so it takes on a positive charge Ca Ionic Compounds Ca+2

  7. The non metal receives one or more electrons to fill its outer shell and become stable. If we draw the Lewis Structure for a non metal, we can see they have a lot more valence electrons. Again, using the arrows that indicate the transferred electrons Having gained two electrons, the Oxygen is now negative. The resulting positive metal and negative nonmetal stick together by electrostatic attraction. O -2 O Ionic Compounds

  8. Putting the compound together, we can see that the overall molecule has a neutral charge. This particular example is simple because the Calcium and Oxygen want to exchange the same number of electrons. What would happen if they wanted to exchange different numbers of electrons? -2 O Ionic Compounds Ca+2 +2 – 2 = 0

  9. First draw the Lewis structures of the atoms on their own. Now use an arrow to show the electron transferring from the Lithium atom to the Oxygen atom You can see that the Oxygen atom still does not have a complete outer shell. Clearly another Lithium atom is required to complete the compound. Li O Li Using Lewis Structures:Ionic bonding between Lithium and Oxygen

  10. The Lithium atoms, having lost one electron each have a charge of +1. The Oxygen atom, having gained two electrons, has a charge of -2. The final Lewis structure is illustrated here. The compound is Li2O. Li+ Li+ -2 O Lithium Oxide continued

  11. Draw the Lewis Structures of the individual atoms. Use arrows to show the transfer of electrons. Aluminum has one electron left, we need another oxygen atom. The oxygen atom now needs more electrons so we need another aluminum atom. The extra electrons on the Aluminum mean we need another Oxygen. Since, we have been able to make both atoms stable, we have hit the correct ratio. Al Al O O O Illustrate the bonding between Aluminum and Oxygen. (Note the ratio here is a little harder to find.)

  12. Having lost 3 electrons, the aluminum has a charge of +3. Having gained 2 electrons, the oxygen has a charge of -2. Now draw the final Lewis Structure. This structure does not necessarily reflect the three dimensional shape of the molecule! It is designed to illustrate the transfer of electrons while bonding. -2 -2 -2 Al+3 Al+3 O O O Aluminum Oxide Continued

  13. Naming Ionic Compounds Naming these compounds is straight forward. • Write the name of the metal • Write the name of the non metal changing the end of the non metal name to – ide. Examples – Sodium Chloride, Calcium Oxide

  14. The trick to finding the ratio of atoms in the molecule. The easiest way is to find the number of BONDS the ion will make (VALENCE NUMBER) is to again refer to your period table Writing the formulas for Ionic Compounds

  15. Number the groups 1-3 going from left to right (skip the Tansition Metals) Number the groups 1-3 going from right to left (skip the Nobel Gases) Writing the formulas for Ionic Compounds 1 2 3 2 1 3

  16. Those numbers represent the charge the ion will have It also tells us the number of bonds it will make Writing the formulas for Ionic Compounds 1 2 3 2 1 3

  17. Write out the atoms with their stable charge (or valence) Al+3O-2 Cross over the numbers to the opposite atom. Al2O3 If possible reduce to lowest terms. Then …

  18. Step 4: AlCl 3 Criss-Cross Rule Example: Aluminum Chloride Step 1: Aluminum Chloride write out name with space Al Cl +3 -1 Step 2: write symbols & valence number Al Cl Step 3: 1 3 criss-cross valence number as subscripts combine as formula unit (“1” is never shown) - Reduce if possible

  19. Criss-Cross Rule Example: Aluminum Chloride Step 1: Aluminum Chloride Step 2: Al+3 Cl-1 Step 3: Al Cl 1 3 Step 4: AlCl 3

  20. Criss-Cross Rule Example: Magnesium Oxide Step 1: Magnesium Oxide Step 2: Mg+2 O-2 Step 3: Mg O 2 2 Step 4: Mg2O2 Step 5: MgO

  21. These will include the transition metals When atoms get larger, their atomic structure can become more complex. This means that some atoms can have different numbers of valence electrons in different situations. For example if we look at the Lewis structure of Copper. It can have one valence electron or two valence electrons. Clearly, this atom can form more than one type of molecule. -2 -2 O O Cu Cu Cu+1 Cu+1 Cu+2 Multivalent Compounds

  22. In terms of naming these compounds, we need a method of distinguishing, CuO and Cu2O You need to put a roman numeral to indicate the valence in brackets in between the metal and non metal. The roman numeral is only included if the metal is one of the atoms that can exhibit more than one valence. This information will be provided! e.g. Write the name for the following compounds, CuF Copper (I) Flouride PbI2 Lead (II) Iodide CaF2 Calcium Flouride Multivalent Compounds

  23. How do we know which roman numeral is being used? • CuF • Do the reverse of the criss cross method • Take the subscript and use it as the charge on the opposite symbol • Cu 1 F1 Cu +1 F-1 • Copper (I) Flouride • PbI2 Pb 1 I2 Pb +1 I-2 • Lead (II) Iodide

  24. Ionic Compounds • Many ionic compounds are soluble in water. • When they dissolve, they separate into ions. • Water molecules surround each ion preventing them from rejoining

  25. Ionic Compounds Properties • They are hard, brittle solids with high melting points • Many are also electrolytes which means they conduct electricity when dissolved in water • Pure water is a poor conductor of electricity, dissolved ions improve this property considerably

  26. Ionic Compound Worksheets

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