Chemistry 103 Lecture 10

EXAM I Survey How did you do on this exam? (Grade range, don’t give your actual score) Did your performance meet your expectations? Did you complete and check the practice exam? Did you finish all homework? If you did not meet your performance expectations, what will you do differently next time? Please list any recommendations for improving the course.

Outline I. Ionic Compounds (in review)  Nomenclature  Polyatomic Ions/Nomenclature II. Covalent Compounds  Lewis Dot Diagrams/Lewis structures  Nomenclature  Properties predicted EXAM I SURVEY

Bonds Ionic Bonds - electron transfer process. Typically between a metal and a nonmetals Covalent Bonds - electrons shared. Typically involving nonmetals.

Ionic and Covalent Bonds Atoms acquire octets To become more stable By losing, gaining, or sharing valence electrons By forming ionic bonds or covalent bonds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

Metal Ions – Why Are They Positive? Let’s look at Mg. Its electron configuration is 1s 2 2s 2 2p 6 3s 2.  If it loses two electrons to become Mg 2+, it will have the electron configuration 1s 2 2s 2 2p 6 8 Valence Electrons!  If it gains 6 electrons to become Mg 6-, it will have the electron configuration 1s 2 2s 2 2p 6 3s 2 3p 6 8 Valence Electrons!  The question is which is easier? To lose TWO electrons or to gain SIX? Losing two: Therefore, Mg tends to form Mg 2+ ions

Nonmetal Ions – Why Are They Negative? Let’s look at Cl. Its electron configuration is 1s 2 2s 2 2p 6 3s 2 3p 5.  If it loses seven electrons to become Cl 7+, it will have the electron configuration 1s 2 2s 2 2p 6 8 Valence Electrons!  If it gains 1 electron to become Cl -, it will have the electron configuration 1s 2 2s 2 2p 6 3s 2 3p 6 8 Valence Electrons!  The question is which is easier? To lose SEVEN electrons or to gain ONE? Gaining ONE: Therefore, Cl tends to form Cl - ions

Elements in a Compound “Table salt” is a compound that contains the elements sodium and chlorine. Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

9 Salt is An Ionic Compound Sodium chloride in “table salt” is an example of an ionic compound. Chemical Formula: NaCl Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

IONIC COMPOUNDS - Lewis Dot Diagrams/Chemical Formulas Ca and Br Li and O

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

NOMENCLATURE ( Metal + Nonmetal ) IONIC COMPOUNDS Metal Metal (fixed charge) (variable charge) ?

Monovalent Positive Ions (ions with only one charge)

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

Naming Ionic Compounds First word of name:  Name of metal in full  If the metal can have more than one positive charge, the charge is indicated in parentheses in the name. Examples: Cu + = copper (I); Cu 2+ = copper (II). Second word of name:  Name of anion (second element in formula) with “-ide” ending

Anion Stems

Examples K 3 N AuCl 3 PbS Chromium (III) oxide Iron (II) oxide Magnesium Chloride

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

19 Learning Check The correct formula for each of the following is: 1. Copper (I) nitride A) CuNB) CuN 3 C) Cu 3 N 2. Lead (IV) oxide A) PbO 2 B) PbO C) Pb 2 O 4

20 Learning Check The correct formula for each of the following is: 1. Copper (I) nitride A) CuNB) CuN 3 C) Cu 3 N 2. Lead (IV) oxide A) PbO 2 B) PbO C) Pb 2 O 4

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

22 NO 3 - nitrate NO 2 - nitrite OH - hydroxide SO 4 2- sulfate SO 3 2- sulfite CO 3 2- carbonate PO 4 3- phosphate NH 4 + ammonium Polyatomic Ions to Memorize

What if the Cation or the Anion is a Polyatomic Ion? Name of polyatomic ion replaces the first word of the name (if the polyatomic ion is positive) or the second word of the name (if the polyatomic ion is negative)  NH 4 Cl  K 2 SO 4  Co 2 (CO 3 ) 3  Ammonium nitrate

What if the Cation or the Anion is a Polyatomic Ion? Name of polyatomic ion replaces the first word of the name (if the polyatomic ion is positive) or the second word of the name (if the polyatomic ion is negative)  NH 4 ClAmmonium Chloride  K 2 SO 4 Potassium Sulfate  Co 2 (CO 3 ) 3 Cobalt(III) Carbonate  Ammonium nitrateNH 4 NO 3

Molecules and Covalent Compounds

Molecules Molecules are made up of two or more atoms, either of the same element or of two or more different elements, joined by one or more covalent chemical bonds (shared electrons).

Molecular Compounds Molecular Compounds are made up of two or more atoms of two or more different elements, joined by one or more covalent chemical bonds (shared electrons).

Lewis Structures/Electron Dot Diagrams Lewis structures show us how atoms are bonded to each other. They can be used to predict molecular shapes, bond strength and bond length.

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

Covalent Bonds & Lewis Structures Formed when two (or more) nonmetals share valence electrons in order to obey the octet rule.  Single bond: two atoms share a pair of electrons between them (2 shared electrons = 1 bond)  Example: H 2

Forming a H 2 Molecule Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

H 2, A Covalent Molecule (Elemental Form) In a hydrogen (H 2 ) molecule Two hydrogen atoms share electrons to form a covalent single bond. Each H atom acquires two (2) electrons. Each H becomes stable like helium (He). Copyright © 2008 by Pearson Education, Inc. Publishing as Benjamin Cummings

Single Covalent Bonds More examples:  Cl 2  HCl  CCl 4

Lewis Structures continued…. Draw the Lewis Structure for O 2.

Double Bonds  Double bond: two atoms share 2 pairs of electrons between them (4 shared electrons = 2 bonds) in order to obey the octet rule

Lewis Structure continued…. Draw the Lewis structure for N 2.