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)

Polar and Non-polar Covalent Bonds Though atoms often form compounds by sharing electrons, the electrons are not always shared equally. If the electrons are shared equally it is a non-polar covalent bond If the electrons are not shared equally it is a polar covalent bond

Properties of Covalent Compounds Most have low melting points and low boiling points. Many are liquids and gases at room temperature. Polar covalent molecules dissolve in water. Nonconductors of electricity.

Lewis Structures Using an atoms dot diagram we can predict how different atoms will bond covalently to form molecules Each bond between atoms requires each atom to share one electron with the other atom. Example: F F F - F

NH3 H N H H H N H H Dot Diagram Steps 1. Draw out atoms with valence electrons (dot structures) 2. Connect 2 e- to share until all atoms have full shells 3. Redraw with connected electrons as the bond 4. Redraw any lone pairs of electrons not involved with bonding NH3 H N H H Hydrogen only needs two electrons to fill its outer shell. Everyone else needs eight electrons in their outer shell. H N H H

Double and Triple bonds Sometimes more than one pair of electrons are shared to meet the octet rule Double Bonds= 2 pairs of electrons shared between two atoms Triple Bonds= 3 pairs of electrons shared between two atoms

Covalent Lewis Structures: Multiple Bonds When two electron pairs are shared between two atoms, the resulting bond is a double bond. these bonds are shorter and stronger than single bonds Consider oxygen gas: 8

Covalent Lewis Structures: Multiple Bonds When three electron pairs are shared between two atoms, the resulting bond is a triple bond these bonds are shorter and stronger than double or single bonds Consider nitrogen gas: 9

Some Clues for Drawing Dot Diagrams Put the single atom in the middle of the dot diagram (the one that will have the most bonds) Hydrogen is never in the middle of the dot diagram H When redrawing, we use dashes to represent 2 shared electrons Remember to redraw the nonbonding electrons Resonance means there are many possibilities and all are present. (Example: SO3) N H H

Practice Drawing Draw dot diagrams for the following: CH4 PCl3 SH2 COH2 H H-C-H .. H-S H : .. : O=C-H H

Exceptions to the Octet Rule The Lewis structure for NO (having odd number of electrons) 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) 12

Lewis Structures B C N O F some common bonding patterns C = 4 bonds & 0 lone pairs Different bonding combinations: 4 single bonds 2 double bonds 1 single + 1 triple bond 2 single + 1 double bond N = 3 bonds & 1 lone pair O = 2 bonds & 2 lone pairs H and halogen = 1 bond B = 3 bonds & 0 lone pairs B C N O F 13

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 CO2 NO3 Carbon tetrachloride Phosphorus trichloride Sulfur dihydride Carbon dioxide Nitrogen trioxide

Common Covalent Compounds Diatomic Elements elements that always occur in pairs name these using the element name Common Covalent Compounds H2O Water NH3 Ammonia CH4 Methane

Acid Nomenclature

How to identify an acid: The formula of an acid starts with “H” (for now) HCl hydrochloric acid

How to identify an acid: The formula of an acid starts with “H” (for now) HNO3 nitric acid

How to identify an acid: The formula of an acid starts with “H” (for now) 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 CH₃COOH HF H₃PO₃ H₂CO₃ HNO₂ H₃PO₄ H₂S