Chemistry 103 Lecture 11

Outline I. Ionic Compounds (in review) II. Covalent Compounds  Lewis Dot Diagrams/Lewis structures  Properties predicted  Nomenclature  Bond Polarity

Ionic vs. Covalent NaCl (sodium chloride) CH 4 (methane)

Nomenclature - Naming Compounds FIRST QUESTION: IONIC or COVALENT???? IONIC NOMENCLATURE RULES (Metal + Nonmetal)

Periodic Table and Some Ions Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

6 Learning Check Select the correct name for each: 1. Fe 2 S 3 A) iron sulfide B) iron(II) sulfide C) iron (III) sulfide 2. CuO A) copper oxide B) copper(I) oxide C) copper (II) oxide

Polyatomic Ions Polyatomic ion  An ion formed from a group of atoms (held together by covalent bonds) through loss or gain of electrons  Can be the positive or the negative ion in an ionic compound

8 Learning Check Name the following compounds: A. Ca 3 (PO 4 ) 2 Calcium Phosphate B. FeBr 3 Iron (III) Bromide C. Al 2 S 3 Aluminum Sulfide D. MgSO 4 Magnesium Sulfate

9 Learning Check Write the formulas for each of the following: A. calcium nitrateCa(NO 3 ) 2 B. iron(II) hydroxideFe(OH) 2 C. aluminum carbonateAl 2 (CO 3 ) 3 D. lithium phosphateLi 3 PO 4

Molecules and Covalent Compounds

11 Diatomic Elements These elements share electrons to form diatomic, covalent molecules.

Electron-Dot Diagrams (Lewis Structures) Electron-dot diagrams show The order of bonded atoms in a covalent compound. The bonding pairs of electrons between atoms. The unshared (lone) valence electrons. (nonbonding) A central atom with an octet. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Multiple Bonds in N 2 In nitrogen N 2, Octets are achieved by sharing three pairs of electrons, which is a triple bond. Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Lewis Structures continued… H 2 O C 2 H 4 C 2 H 2

Properties of Bonds Bond Length  Distance between 2 nuclei  Triple bond < Double Bond < Single Bond Bond Strength  Energy required to separate 2 nuclei  Triple bond > Double Bond > Single Bond

Lewis Dot Structures Example: CO :C : : : O: Coordinate Covalent Bonds - bond in which there is an uneven contribution of the shared electron pairs.

Lewis Dot Structures extended As long as all the atoms in your molecule are satisfied under the octet rule (exception is H with only 2 electrons), then you have an acceptable Lewis Dot Structure. Not always easy to decide how to position electrons in a molecule to form the “stable 8” configuration for each atom.

Drawing Lewis Structures Example: SO 3 1.Determine the arrangement of the atoms in the molecule. (Symmetry is key - first atom usually is the central atom unless it is an H) O S O O

Drawing Lewis Structures, continued 2. Determine the total number of valence electrons present. O S O O S = 6 valence electrons O = 6 valence electrons x 3 = 18 TOTAL = 24

Drawing Lewis Structures, continued… 3. Determine the total number of valence electrons the molecule (or ion) will need to have a noble gas configuration. Nobel Gas Count H 2 S, O, F, … 8

Drawing Lewis Structures, continued… 3. Determine the total number of valence electrons the molecule (or ion) will need to have a noble gas configuration. O S O O Valence count = 24 Noble Gas count = 8 x 4 = 32

Drawing Lewis Structures, continued… 4. Determine the number of bonding electron pairs needed: Noble Gas count (step 3) - Valence (step 2) 2 = Total number of bonds SO = 4 bonds 2

Drawing Lewis Structures, continued… 5. Write in the skeletal structure, the bonding electron pairs and the nonbonding pairs of electrons to satisfy octet rule. 6. Check the electron dot structure to confirm that the total number of electrons present is the same as the valence count in step 2 THIS ONLY WORKS FOR SYSTEMS THAT FOLLOW THE OCTET RULE - NO EXCEPTIONS!!!!

Resonance Structures Two or more Lewis Dot structures that have the same arrangement of atoms and the same number of electrons, but differ in the location of the electrons (bonds)

Lewis Dot Structure Draw the Lewis Dot Structure for Nitrate (NO 3 - )

Resonance structures for NO 3 − are −   −   − : O : : O : : O : ║ │ │ N N N : O : : O : : O : : O : : O : : O :         Resonance Structures

NOMENCLATURE Naming covalent compounds

Nomenclature - Naming Compounds FIRST QUESTION: IONIC or COVALENT???? IONIC RULES COVALENT RULES (Metal + Nonmetal) (Nonmetals)

Naming Covalent Compounds Covalent Compounds Greek Prefixes Common Names H-first (BINARY = 2 ELEMENTS)

Naming Binary Covalent Compounds First word of name:  Greek prefix + name of first element Note: if the prefix would be “mono” for the first element, the prefix is not included Note: when an element name begins with a vowel, an a or o at the end of the Greek prefix is dropped for phonetic reasons Second word of name  Greek prefix + stem of name of second element with “-ide” ending

Greek Prefixes Table in text 1 mono6 hexa 2 di7 hepta 3 tri8 octa 4 tetra9 nona 5 penta10 deca

Naming Covalent Compounds Examples:  P 4 O 10  CO  CO 2  NCl 3  N 2 O 5

Naming Covalent Compounds Covalent Compounds Greek Prefixes Common Names H-first

Common Names H 2 O water H 2 O 2 hydrogen peroxide CH 4 methane NH 3 ammonia PH 3 phosphine

Naming Covalent Compounds Covalent Compounds Greek Prefixes Common Names H-first

Hydrogen First in compound HClhydrogen chloride H 2 SO 4 hydrogen sulfate H 3 PO 4 hydrogen phosphate When in water (aq) has very different properties – ACIDS HCl(aq)hydrochloric acid H 2 SO 4 (aq)Sulfuric Acid H 3 PO 4 (aq)Phosphoric Acid