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Chemistry

Understand the formation of ionic compounds, the transfer of electrons between metals and non-metals, and how to name these compounds.

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Chemistry

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  1. Chemistry Ionic Compounds

  2. Ionic Compounds

  3. Recall Ions • “+” on the left (metals) because they lose electrons (become less negative) • “-” on the right (non-metals) because they gain electrons (become more negative) • What is the total charge if you have X+1 and Y-1 • (+1) + (-1) = 0, therefore the total charge is neutral or 0

  4. Ionic Compounds 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

  5. Ionic Compounds Ionic compounds are formed when a metal gives one or more of its electrons to a non metal. When all of the electrons are gone, the metal’s inner orbit of electrons is full. So, the metal is stable. The Lewis diagram is just the symbol and the charge The atom has lost electrons so it takes on a positive charge Ca Ionic Compounds Ca+2

  6. Ionic Compounds 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 include the full valence orbit, brackets and a charge 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

  7. Ionic Compounds Putting the compound together, we can see that the overall molecule has a neutral charge (no 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 Try it! Li and O

  8. Using Lewis Structures:Ionic bonding between Lithium and Oxygen 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

  9. Using Lewis Structures:Ionic bonding between Lithium and Oxygen 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 Gizmo Demo

  10. 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. • Illustrate the bonding between Aluminum and Oxygen. (Note the ratio here is a little harder to find.) Al Al O O O Gizmo Demo

  11. 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 is designed to illustrate the transfer of electrons while bonding. • Aluminum and Oxygen -2 -2 -2 Al+3 Al+3 O O O Aluminum Oxide Continued

  12. Naming Ionic Compounds Naming Ionic Compounds • 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

  13. 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 is to again refer to your period table – as we did last day • Writing the Chemical Formula Writing the formulas for Ionic Compounds

  14. Number the groups 1-3 going from left to right (skip the Transition Metals) Number the groups 1-3 going from right to left (skip the Nobel Gases) • Writing the Chemical Formula Writing the formulas for Ionic Compounds 1 2 3 2 1 3

  15. Those numbers represent the charge the ion will have It also tells us the number of bonds it will make • Writing the Chemical Formula Writing the formulas for Ionic Compounds +1 +2 -3 -2 -1 +3

  16. Write out the atoms with their stable charge Al+3O-2 Cross over the numbers to the opposite atom and remove the sign – This is the Criss-Cross Rule Al2O3 If possible reduce to lowest terms. • The Criss-Cross Rule Then …

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

  18. The 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

  19. 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. • Multivalent Compounds -2 -2 O O Cu Cu Cu+1 Cu+1 Cu+2

  20. Naming Multivalent Ions • We need to distinguish between the two or three different ion forms • Use roman numerals from I – VII which corresponds to 1+  7+ ion charges • For example: • Nickel can have two ion forms, Ni2+ and Ni3+ • These are named nickel (II) and Nickel (III) Metal Ion charge Roman Numeral 1+ I 2+ II 3+ III 4+ IV 5+ V 6+ VI 7+ VII

  21. 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 charge in brackets in between the metal and non metal. Remember it is the original charge The roman numeral is only included if the metal is one of the atoms that can exhibit more than one charge. This information will be provided! e.g. Try to write the name for the following compounds without looking at the next slide CuF PbI2 CaF2 • Naming Multivalent Compounds Multivalent Compounds Copper (I) Fluoride Lead (II) Iodide Calcium Fluoride

  22. Naming Multivalent Compounds How do we know which roman numeral is being used? • 1) CuF • Do the reverse of the criss cross method • Take the subscript and use it as the charge on the opposite symbol • Put the charge for the metal in brackets •  Copper (I) Flouride • 2) PbI2 •  Lead (II) Iodide Cu +1 F-1 Cu 1 F1 Pb+2 I-1 Pb1 I2

  23. Silver (Ag) – always has a charge of +1 • Zinc (Zn) – always has a charge of +2 • Be careful when you are asked to determine the roman numeral given the formula (e.g. CuS) • This would lead you to answer: Copper (I) Sulfide • However we ALWAYS NEED TO CHECK THAT THE CHARGE ON THE ANION IS CORRECT • In this case it would be -1 however, if we look at the periodic table we know that S is -2 • Therefore we need to multiply both charges by 2 • Copper (II) Sulfide • MAKE SURE YOU CHECK THAT THE CHARGE ON THE NON-METAL IS CORRECT!!

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

  25. Properties of Ionic Compounds • 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

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