Demo Salt Crystal (hanging on ceiling) Covalent Compounds Demo Salt Crystal (hanging on ceiling) Videodisk Unit 3

Covalent Bonding Takes place between two non-metals Electrons are shared by both nuclei to help each attain 8 valence electrons There are several electrostatic interactions in these bonds: Attractions between electrons and nuclei Repulsions between electrons Repulsions between nuclei A molecule is formed when two or more atoms bond covalently Covalent Bond Video (25 sec) Ionic and Covalent (2 min)

Properties of Covalent Compounds Drawing the Lewis Dot Diagram of a molecule helps determine the specific properties. Properties of Covalent Compounds Most have low melting points and low boiling points. Many are liquids and gases at room temperature. Nonconductors of electricity. AKA Nonelectrolytes

NH3 H H N H Lewis Dot Diagram Steps 1. Add up the number of valence electrons on each atom in the molecule: 5 + 1 + 1 +1 = 8 2. Draw the central atom and use sticks (two electrons) to connect the terminal atoms to the central. 3. Be certain all atoms other than hydrogen have an octet. Use lone pairs on central if necessary. 4. Make double bonds if there are not enough electrons left for the central atom’s octet. NH3 H H N H Hydrogen only needs two electrons to fill its outer shell. Everyone else needs eight electrons in their outer shell.

Draw dot diagrams for the following: CH4 N2 PCl3 CO2 SH2 O2 BH3 H H-C-H H-S H .. : H-B-H H

Exceptions to the Octet Rule The Lewis structure that deals with boron (B): boron shares 3 electrons to form three single bonds The Lewis structures of SF6 and PCl5 (for elements in Period 3 or greater) 6

Comparing length and strength of single, double and triple bonds Use a model kit to construct these three molecules. How are the distances between the carbon atoms different?

Relative lengths: single bond ˃ double bond ˃ triple bond Relative strengths: triple bond ˃ double bond ˃ single bond

Dinitrogen Pentaoxide Naming Covalent Bonds Write names of both elements Add -ide to the last name Add prefixes at beginning of each word to indicate how many of each element. Exception- do not use mono in front of the first element N2O5 Dinitrogen Pentaoxide

Covalent Bonding Prefixes (mono-) di- tri- tetra- penta- hexa- hepta- octa- nona- deca-

Practice Naming Name the following: CCl4 PCl3 SH2 CO NO3 N2O4 Carbon tetrachloride Phosphorus trichloride Sulfur dihydride Carbon monoxide Nitrogen trioxide Dinitrogen tetraoxide

Molecular Elements H2 N2 O2 F2 Common Covalent Compounds Cl2 Br2 I2 Certain elements occur as 2 atom molecules Rule of 7’s there are 7 common diatomic elements find the element with atomic number 7, N make a figure 7 by going over to Group 7A, then down don’t forget to include H2 VIIA 7 H2 N2 O2 F2 Common Covalent Compounds Cl2 Br2 H2O Water NH3 Ammonia CH4 Methane I2

Acid Nomenclature

How to identify an acid: The formula of an acid starts with “H” HCl hydrochloric acid HNO3 nitric acid H3PO4 phosphoric acid

1. Binary Acids (Two elements, one of which is hydrogen) HCl HBr H2S Two types of acids: 1. Binary Acids (Two elements, one of which is hydrogen) HCl HBr H2S 2. Oxyacids (contain oxygen, usually a polyatomic ion bonded to hydrogen) H2SO4 HClO3 HClO4

If it is a binary acid: Prefix = Hydro- root = second element’s name Suffix = -ic acid HCl = hydro- chlor -ic acid→ hydrochloric acid HBr= hydro- brom -ic acid →hydrobromic acid H2S = hydro – sulfur – ic acid →hydrosulfuric acid

If it is an oxyacid Prefix = none root = anion (polyatomic name) Suffix =depends! + acid If anion ends in –ate replace with –ic acid If anion ends in –ite replace with –ous acid Example: HNO₃ Example: HNO₂ Since NO₃⁻ = Nitrate Since NO₂⁻ = Nitrite HNO₃ = Nitric Acid HNO₂ = Nitrous acid *Sulfate/ite root goes to sulfur (sulfuric and sulfurous acid). Same is true for phosphate

Examples HNO2 H2SO3 H3PO4 HNO3 HCl H2SO4

Examples- answers nitrous acid sulfurous acid phosphoric acid nitric acid hydrochloric acid sulfuric acid

Try on your own 1. HCl 2. HBr 3. H₂SO₄ 4. H₂S 5. H₂CO₃ 6. HC₂H₃O₂ 7. H₃PO₄ 8. H₃P 9. H₂CrO₄ 10. H₂Cr

Answers 1. HCl- hydrochloric acid 2. HBr- hydrobromic acid 3. H₂SO₄- sulfuric acid 4. H₂S- hydrosulfuric acid 5. H₂CO₃- carbonic acid 6. HC₂H₃O₂- acetic acid 7. H₃PO₄- phosphoric acid 8. H₃P- hydrophosphoric acid 9. H₂CrO₄- chromic acid 10. H₂Cr- hydrochromic acid

Try writing the formulas: Sulfuric acid Nitric acid Hydrochloric acid Acetic acid Hydrofluoric acid Phosphorous acid Carbonic acid Nitrous acid Phosphoric acid Hydrosulfuric acid

Answers H₂SO₄ HNO₃ HCl HC2H3O2 HF H₃PO₃ H₂CO₃ HNO₂ H₃PO₄ H₂S