Chemistry 103

Lecture 9

Outline

I. Chemical Bonds - Ionic Compounds (CH6) Electron Dot Symbols Lewis Dot Diagrams Predicting Formulas

Bonds

Chemical bond: attractive force holding two or more atoms together.

Bonds

Ionic Bonds - electron transfer process. Typically between a metal and a nonmetals

Covalent Bonds - electrons shared. Typically involving nonmetals.

The Representative Elements

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Rules for Electron Dot Symbols 1. Representative elements in the same

group of the periodic table have the same number of valence electrons

2. The number of valence electrons is represented by “dots” around the symbol of the representative element.

3. The maximum number of valence electrons for any representative element is 8 - Octet Rule.

Learning Check - Aluminum (Al)

1. Number of valence electrons in aluminum is:

A) 1 B) 2 C) 3

2. In Al, the change in electrons to achieve an octet is:

A) loss of 3e- B) gain of 3e- C) a gain of 5e-

3. The Ionic charge of aluminum is:

A) 3- B) 5- C) 3+

4. The symbol for the aluminum ion is:

A) Al3+ B) Al3- C) Al+

1. Number of valence electrons in sulfur is:

A) 4e- B) 6e- C) 8e-

2. Change in electrons for octet requires a:

A) loss of 2e- B) gain of 2e- C) a gain of 4e-

3. Ionic charge of sulfur is:

A) 2+ B) 2- C) 4-

Learning Check

Predicting Ionic Charge

• The number of electrons an atom loses is related to its position on the periodic table.

The Periodic Table and Ions Group IA metals - +1 Group IIA metals - +2 Group IIIA metals - +3 Group VIIA nonmetals - -1 Group VIA nonmetals - -2 Group VA nonmetals - -3

11

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

Chemical Formulas of Ionic Compounds

For a neutral species, the number of electrons lost and gained must be equal.• The amount of positive charge must equal the

amount of negative charge.Formulas of ionic compounds

Symbol for the positive ion is always written first The charges on the ions are NOT shown in the

formula The subscripts in the formula give the combining

ratio for the ions

Lewis Dot Diagrams

Using the Electron Dot Symbols, write the Lewis Dot Diagram and the Chemical Formula for

Na and Cl

Ionic Formula of NaCl

In an ionic formula,

• The symbol of the metal is written first followed by the symbol of the nonmetal

• The charges of the ions in the compound are not shown

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Lewis Dot Diagrams continued…• Example: What is the Lewis Dot Diagram

and the chemical formula for the ionic compound formed between Mg and Cl?

Charge Balance In MgCl2

In MgCl2• An Mg atom loses

two valence electrons

• Two Cl atoms each gain one electron

Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings

Dot Diagrams & Chemical Formulas

Write the Lewis Dot Diagrams and give the chemical formulas for the ionic compounds formed between the following elements

Na and O

Ca and O

Al and O

Writing Ionic Formulas from ChargesCharge balance is used to write the formula for

sodium nitride, a compound containing Na+ and N3−.

Na+

3 Na+ N3- = Na3N

Na+

3(+1) + 1(3-) = 0

Ionic Chemical Formulas

Give the chemical formula for the ionic compounds made from the following elements:

1. K and F

2. Mg and S

3. Al and S

4. Li and N

Chapter 2 - Measurements

Measurements

Sig Figs” Identifying Rounding Math Operations

Dimensional Analysis Percent Factor Density

Chapter 3 - Matter (and Energy) Chemical vs.Physical

Matter Classified Element Compound Homogeneous Mixture Heterogeneous Mixture

Chapter 4 - Atoms & Elements Periodic Table Symbols for Elements The Atom

History Subatomic Particles

Atomic Symbols Isotopes, Ions

Atomic Mass (amu)

Chapter 5 (Ch4) - Electronic Structure Electromagnetic

Radiation Classical vs Quantum

History Quantum Numbers Electron Configurations Orbital Diagrams Valence Atomic Radii

Practice Problem

The density of diamond is 3.51g/mL. What is the volume (in liters) of the Hope diamond if it has a mass of 44.0 carats?

(1 carat = 0.200g)

Practice Multiple Choice

1). Which species has 16 neutrons?

a. 31P b. 34

S2- c. 36

Cl d. 89Br

- e. none of these

(p = 15) (p = 14) (p=17) (p=35)

2). An isotope of which element is used as the standard for the relative mass scale for atoms?

a. nitrogen b. oxygen c. hydrogen d. gold e. none of these

Practice Multiple Choice

3). Which of the following elements is expected to be chemically similar to calcium (Ca).

a. K b. Sc c. Cl d. Mg e. Al

4). A g-orbital has an “l” quantum number of 4. How many total electrons can this subshell hold?

a. 4 b. 6 c. 18 d. 10 e. 14

l = 4, ml = -4,-3,-2,-1,0,1,2,3,4 (9 values = 9 orbitals x 2 = 18 electrons)