Protons, neutrons, electrons, the periodic chart, atoms and molecules...
it's all here. The foundation for the balance of CHEM 200 is laid here,
in Chapter Two.
Chapter 2 Outline
2.1 Elements, Compounds & Mixtures: An Atomic Overview
2.2 Observations That Led to an Atomic View of Matter
2.3 Observations that Led to the Nuclear Atom Model
2.5 Elements: A First Look at the Periodic Table
2.6 Compounds: Introduction to Bonding
Breakdown, Brief Discussion & Help With Sample Problems: What You Should Know
2.1 Elements, Compounds & Mixtures: An Atomic Overview
This section includes four important definitions: element, molecule, compound, and mixture. These terms are used throughout the rest of the semester; knowledge of their definitions and proper usage is therefore important.
2.2 Observations That Led to an Atomic View of Matter
The arithmetic component of CHEM 200 starts to rear its ugly head in this section. Chemists always want to know how much of something consists of X, consists of Y, and so on. Those cacluations are often called percent by mass calculations...and Sample Problem 2.1 illustrates the concept quite nicely.
click here for a few words about SAMPLE PROBLEM 2.1 (page 43)
More terms are discussed, though, including the law of mass conservation and the law of multiple proportions. CHEM 200 students should know these terms, and know why they're important. For example, it is the law of mass conservation (i.e. the total mass of substances dose not change during a chemical reaction) that requires that all chemical equations be balanced--a task CHEM 200 students tackle later in the semesters
Section 2.2 also contains includes a discussion and summary of John Dalton's theory of matter, a theory which explains the aforementioned mass laws.
2.3 Observations that Led to the Nuclear Atom Model
This section is again largely a historical description of discoveries made, largely by physicists, late in the 19th and early in the 20th centuries. Specifically, JJ Thomson and Robert Millikan carried out important experiments that were critical in the development of scientists' understanding of the electron...while Ernest Rutherford's work indicated the existence of the nucleus, which he postulated contained positive charge and essentially all of the mass of the atom.
Reading section 2.3 exposes CHEM 200 students to the scientific uses of the cathode ray tube...better known in 1998 as the picture tube within a direct view television.
No history here--just the facts. The structure of the atom (protons, neutrons, and electrons) is discussed, and the language and jargon of the Periodic Table of the Elements is introduced.
CHEM 200 students should familiarize themselves with the following terms: atomic number (Z); mass number (A); atomic symbol; isotopes; atomic mass unit (amu); isotopic mass; and atomic mass.
The building-block nature of this section cannot be over-emphasized. For example, a competent CHEM 200 student, at this point in the class, should be able to fully decipher the left-hand margin of page 52...which requires knowledge of the aforementioned terms (atomic number (Z); mass number (A); atomic symbol; isotopes, atomic mass unit (amu), isotopic mass; and atomic mass). Sample Problem 2.2 is another good place to begin testing your knowledge of these concepts.
click here for a few words about SAMPLE PROBLEM 2.3 (page 54)
AN EXTRA: The graphics on pages 54 and 55 describe the technique and theory of mass spectrometry, a technique that scientists use to measure the mass and abundance of charged particles.
2.5 Elements: A First Look at the Periodic Table
One of the major achievements of modern mankind is the development of the Periodic Table of the Elements.
The main goal of this section is to give CHEM 200 students the tools to decipher certain aspects of the Periodic Table. Terms to know include groups (vertical columns), periods (horizontal rows), metals, nonmetals, metalloids, alkali metals and alkaline earth metals. Mastery of these terms enables CHEM 200 students to begin to understand why the table of the elements is referred to as the PERIODIC table of the elements...there are specific attributes that certain elements possess that can be predicted on the basis of their position in the table.
A take-home message from section 2.5: elements in a group (vertical column) have similar chemical properties and elements in a period (horizontal row) have different chemical properties.
For example, while the Group 7A elements (including F, Cl, Br, and I) all form ionic compounds with Na...in a one-to-one ratio...those very same elements for ionic compounds with Mg in a two-to-one ratio.
Successful CHEM 200 students become very familiar with page 58 of Silberberg's text--a five-color diagram of the Periodic Table of the Elements.
2.6 Compounds: Introduction to Bonding
Most chemists are concerned with molecules...and molecules are formed when their constituent atoms are connected via chemical bonds.
There are two broad categories of compounds: ionic compounds and covalent compounds.
Ionic compounds are composed of ions (anions and cations)...and result when one atom or molecule interacts with another atom or molecule in such a way that results in one of the two entities transferring an electron to the other.
Table salt (NaCl; sodium chloride) is an example of an ionic compound. The formation of sodium chloride is nicely depicted in Fig 2.14 of Silberberg (p. 60).
The bond within sodium chloride is referred to as an ionic bond.
On the other hand, covalent componds form when elements share electrons...which usually occurs between non-metals. Fig 2.16 in Silberberg (p. 62) depicts the covalent bond that forms when one hydrogen atom bonds with another hydrogen atom, forming a hydrogen molecule (H2).
The Gallery on p. 63 ("Picturing Molecules") is a nicely informative, and extremely important, part of Chapter 2. Most chemists work with molecules on a daily basis...and to be able to draw and represent molecules, whether on paper, a computer screen, or a blackboard, is an important part of a CHEM 200 student's training. In particular, students who plan to take chemistry courses beyond CHEM 200 should pay particular attention to p. 63.
2.7 Compounds: Formulas, Names & Masses
Section 2.7 includes pages 64 through 73, and is therefore the longest section in the first two chapters of Silberberg's text.
Items in 2.7 include one figure (2.18), four tables, and nine sample problems...so a wise CHEM 200 student will spend a great deal of time and effort on this section.
Of particular importance include the following:
*definitions such as empirical formula, molecular formula, and structural formula
*the names and charges of common monatomic ions (Table 2.3)
*a list of some metals that form more than one monatomic ion (Table 2.4)
*a list of formulas and names of selected common polyatomic ions (Table 2.5)
*the system of naming ions that uses roman numerals and "ic" and "ous" suffixes
*the naming system used for binary and oxoacids (p. 70); and the naming system used for families of oxoanions (p. 68 and 69)Tables 2.3, 2.4, and 2.5 form a large part of the jargon used in the first half of CHEM 200.
Finally, the concept of molecular mass is introduced on page 71. Molecular mass is the first exposure to using the numerical data on the periodic chart (i.e. the atomic weights) in a way similar to what will become second nature later in the semester.
click here for a few words about SAMPLE PROBLEM 2.7 (page 68)
click here for a few words about SAMPLE PROBLEM 2.8 (page 69)
click here for a few words about SAMPLE PROBLEM 2.10 (page 70)
2.8 Mixtures: Classification & Separation
Section 2.8 is a short section that introduces the terms heterogeneous mixture, homogeneous mixture, and solution.
Solutions with water as solvent are referred to as aqueous solutions.
AN EXTRA: The graphic that spans pages 74 and 75 (entitled "Basic Techniques for Separating Mixtures") nicely summarizes the techniques of filtration, crystallization, distilation, extraction, and chromatography.
exercises such as numbers 2.24, 2.41, 2.55, 2.82 and 2.96 are all straightforward problems of the type that are often found on CHEM 200 exams