Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules

1. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules

2. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Lewis Electron-Dot Structures In 1920,G.N. Lewis, the American chemistcame up with a system to represent the valence electrons of an atom. This system - known as electron-dot diagrams or Lewis structures - uses dots to represent valence electrons. Lewis’s system is a valuable model for covalent bonding. A Lewis structure shows only the valence electrons in an atom or molecule. The nuclei and the electrons of the inner energy levels (if any) of an atom are represented by the symbol of the element.

3. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules 1 2 3 4 5 6 7 8

4. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Rules for Electron Dot Structures 1. Each atoms is drawn with its symbol surrounded by one dot for each of its valence numbers. No more than 2 dots to a side. 2. Determine if you are drawing an ionic or covalent substance. Ionic – Must show the charges due to lose/gain of electron(s), anions are to be placed in brackets [ X]2- Covalent – Must show the shared pair(s) of electrons 3. No more than 8 electrons around any atom. (H, He, B, and Be will only have 2) 4. Covalent may have up to 3 bonds between atoms.

5. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Draw dot structures for CH4

6. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Draw dot structures for NaCl

7. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Draw dot structures for H2O

8. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Draw dot structures for NH4+

9. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Draw dot structures for CaSO4

10. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Draw dot structures for MgCl2

11. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Draw dot structures for CO2

12. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Draw dot structures for F2

13. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Naming Covalent Compounds Covalent compounds made of two elements are named by using a method similar to the one used to name ionic compounds. Covalent Compounds usually list the most electronegative element last. This element will have the “–ide” ending that is usually found on ions. The first element listed will keep its periodic table name. For example, SO2 The first element keeps its periodic name -- Sulfur The last element picks up the “–ide” ending -- Oxide

14. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Prefixes Indicate How Many Atoms Are in a Molecule Prefixes are used to tell how many of each element are found in each molecule. A prefix is added to the name of the first element and one is added to the second element. Mono Hexa Di Hepta Tri Octa Nona Tetra Penta Deca

15. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Prefixes are not used on the first element if there is only one of them. SO2 Nitrogen Dioxide Sulfur Dioxide NO2 SO3 Carbon Monoxide Sulfur Trioxide CO P4O6 Dinitrogen Tetraoxide Tetraphosphorus Hexaoxide N2O4

16. The diatomic 7 There are seven molecules that commonly bond with themselves and form a diatomic molecule (molecule with two atoms). These molecules are never found in nature as atoms, only in their diatomic form. They will keep their atomic name. Hydrogen H2 Nitrogen N2 Oxygen O2 Fluorine F2 Chlorine Cl2 Bromine Br2 Iodine I2

17. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Review Which is the correct electron-dot formula for a molecule of chlorine? Which electron-dot diagram best represents a compound that contains both ionic and covalent bonds?

18. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Review Which molecule contains a polar covalent bond? What is the correct Lewis electron-dot structure for the compound magnesium fluoride?

19. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Review Which diagram below shows the correct Lewis electron-dot diagram for a molecule of phosphorus trichloride, PCl3? Which Lewis electron-dot diagram is correct for CO2?

20. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Review • What is the IUPAC name for P2O5? • Phosphorus Oxide • Diphosphorus Pentaoxygen • Diphosphorus Oxide • Diphosphorus Pentaoxide • What is the formula for Nitrogen Disulfide? • NS • N2S • NS2 • N2S2

21. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Review

22. Chapter 6 -Covalent compounds Section 2 - Drawing and Naming Molecules Review