1. Review of Ionic Compounds In an ionic compound, • One element [non-metal], can strongly pull electrons away from other element and become a negative ion [anion],as the element fills it’s valence shell • The other element [metal], is weaker at holding it’s electrons and loses valence electrons & becomes a positive ion [cation]. • METAL + NON-METAL

2. Non-Metal Anions Metal Cations Noble Gases

3. MOLECULAR COMPOUNDS have NON METALS bonding with NON METALS H B C N O F Si P S Cl As Se Br Te I At

4. MOLECULAR COMPOUNDS • Non-metals in molecular compounds SHAREelectrons. • When non-metals share electrons they create a COVALENTbond. Hence, they are also called COVALENTCOMPOUNDS.

5. Both NON METAL elements in a molecular compounds have similar power to pull electrons. So instead of gaining & losing electrons [as in ionic], molecular compounds SHAREelectrons between two NON-METAL elements, like a tug of war between two equals. WHY SHARE ELECTRONS?

6. Example of sharing: A COVALENTBONDbetween 2 fluorine atoms is how diatomic fluorine gas (F2) is formed

7. Another example • This is methane – CH4

8. Different types of covalent bonds form depending on the number of electrons being shared.

9. In molecular compounds a prefix is used to indicate the numberof each atom present. CO2 C O O  carbon dioxide

10. Counting Atoms • CaSO4 • Ca S O OOO • Mg3(PO4)2  • Mg MgMgP P O OOOOOOO

11. MOLECULAR COMPOUNDS • You need to memorize the following prefixes:

12. MOLECULAR COMPOUNDS • If there is only one of the first element we ignore the prefix, • but if there is only one of the second element we write the prefix – mono .

13. WRITING FORMULAS • Use the prefixes to determine the SUBSCRIPTSof each element in the compound. Steps: • Check if compound is molecular (non-metal + non-metal) • Write the symbols of the elements 3. Write the subscript for the number of atoms represented by the prefix. 4. NO REDUCING dinitrogen tetroxide  N2O4 [not NO2] Example 1 - sulphur trioxide SO3 Example 2 - diphosphoruspentasulphide P2S5

14. Practice Questions • sulfur trioxide • carbon dioxide • sulphur hexafluoride • phosphorus trichloride • nitrogen monoxide • SO3 • CO2 • SF6 • PCl3 • NO

15. WRITING NAMES • Writing names is also straight forward. You use the appropriate prefix to indicate the number of atomsof that element. Steps: • Check that compound is molecular. • Determine the appropriate prefix for each element. 3. Write the prefix and the name of the element.

16. Examples • Example 1 - N2O dinitrogenmonoxide • Example 2 - BrI bromine moniodide • Example 3 - XeF4 xenon tetrafluoride

17. Practice Questions 1. N2O4 2. SO2 3. H2O 4. P2O5 5. CF4 6. NCl3

18. Practice Questions - Answers 1. N2O4 2. SO2 3. H2O 4. P2O5 5. CF4 6. NCl3 dinitrogentetroxide* sulfurdioxide dihydrogenmonoxide diphosphorouspentoxide carbon tetrafluoride nitrogen trichloride

19. DIATOMIC ELEMENTS • Some of the elements are gases at room temperature . • Which means they exist naturally as compounds of the same element bonded together. • These elements include: H O N ClF Br I • hydrogen gas H2 • oxygen gas O2 • nitrogen gas N2 • Chlorine gas Cl2 • fluorine gas F2 • Bromine(liquid) Br2 • Iodine(solid) I2

20. OTHER COMMON NAMES OF COMPOUNDS • O3 - ozone • H2O - water • H2O2 - hydrogen peroxide • NH3 - ammonia • CH4 - methane Lets look at their Electron structures

21. It is easier to just look at the valence electrons with a lewis dot structure

22. Combining Capacities of NON-Metals • The number of electrons a non-metal needs to share to become stable is a clue to the number of covalent bonds the element can form • Look to the number of valence electrons and • how many more electrons are needed to achieve a stable valence shell

23. LEWIS DOT STRUCTURESMolecular&ionic compounds

24. Sharing Electrons When NON METAL elements share electrons they create COVALENT BONDS

25. Sharing Electrons When NON METAL elements share electrons they create COVALENT BONDS

26. Lewis Dot for Ionic

27. HOMEWORK • Textbook – Chapter 4.2 • read pages 152 -157 • do question #1 - 4 Page 156, • pg 158, #1 - 7 • do practice problem on page ?