Chapter 2 Outline

This chapter serves as an introduction to atomic theory. The most important concept in this chapter is the idea that everything is composed of atoms. And that there are different types of atoms (elements). This concept is the one of the underlying theories that makes modern chemistry possible. It is the context that allows us to explain what happens.

  1. Protons, Neutrons, and Electrons: A Historical Perspective. This section outlines the ground breaking experiments that lead to the identification of subatomic particles; protons, neutrons, and electrons. You should be familiar with the experiments, how they work and what they explain. The names in this section are some of the greatest in science.

  2. Atomic Number and the Atomic Mass. This section explains how subatomic particles are arranged to make atoms and elements. You should be able to identify the number of protons, neutrons, and electrons in an atom of a given element. The most important points are outlined in the table below.

    Subatomic Particles
    Particle Charge Mass Symbol Significance
    Proton +1 1 u  11p Atomic Number
    Neutron 0 1 u 10n # neutron + # proton = isotope mass
    Electron -1 0 u (0.0005485799 u) 0-1e charge of atom

  3. Isotopes. The identity of an element is determined by the atomic number or the number of protons. However, the number of neutrons is not fixed. Atoms of a given element with different numbers of neutrons are called isotopes. They are chemically identical (almost), but they have slightly different masses. In this section you will need to do calculations with percent abundance.

  4. Atomic Weight. In this section you will calculate the atomic weight for an element. This is a weighted average of the mass for each isotope. Follow the exaples carefully and make certain you understand where the numbers are coming from.

  5. Atoms and the Mole. This section introduces the concept of the mole and of molar mass. This is a key concept in the course. You will use it throughout the year. Understanding what the mole is about is critical to solving modern chemistry problems. The key point is that the mole is a counting unit (like pair, dozen, score, gross). You need to be able to convert from moles to mass or from mass to moles. The section also discusses Avogadro's number. You will use this some, and you should realize how large it is. But it will not be used throught the semester.

  6. The Periodic Table. This section describes the arrangment of elements in the periodic table and the development of the periodic table.

  7. The Elements, their chemistry and the periodic table. This section discusses the gerneral trends in the periodic table. You should be able to locate each of the groups discussed on a periodic table.

  8. Essential Elements. These are the elements that are essential for biological systems.

  9. Molecules and Compounds. Atoms of elements combine to make molecules and compounds. This molecular scale connection makes it possible to solve many questions about what molecules and compounds are composed of and how chemical reactions occur.

  10. Molecular Models. This section discusses ways to visualize molecules and compounds using pictures, computer animations, and physical models. You need to be able to see the molecule in your head. Use all of these tools to help you learn how to do this.

  11. Ions. Many elements are often found as ions, atoms with a charge. You should be able to predict the charge of many elements from the periodic table. The transistion metals can have several different charges, so they must be specified. Atoms become charged when an electron is added or removed. This section also introduces polyatomic ions. These are ions that contain several different atoms, but which are often found together. You must know the polyatomic ions listed in Table 3.1 and given below. If you do not know these YOU WILL GET LOTS OF QUIZ AND EXAM QUESTIONS WRONG

    ammoniumNH4+
    cyanideCN-
    acetateCH3COO-
    carbonateCO32-
    hydrogen carbonateHCO3-
    nitriteNO2-
    nitrateNO3-
    phosphatePO43-
    hydrogen phosphateHPO42-
    dihydrogen phosphateH2PO4-
    hydroxideOH-
    sulfiteSO32-
    sulfateSO42-
    bisulfateHSO4-
    hypochloriteClO-
    chloriteClO2-
    chlorateClO3-
    perchlorateClO4-
    chromateCrO42-
    dichromateCr2O72-
    permanganateMnO4-

  12. Ionic Compounds. Ionic compounds result when a positive and a negative ion combine. These are usually found as extended ionic lattices. This gives them a crystal structure rather than a molecular structure.

  13. Names of Compounds. See nomenclature handout. You MUST know how to name the different types of compounds. Read this section very carefully and get lots of practice.

  14. Atoms, Molecules, and the Mole. This section introduces the mole and discusses conversions between moles and mass. You need to be very good at these conversions, we will do them throughout the rest of the year. The mole is a way to keep track of how many atomes or molecules are present. Since these are what react in a chemical reaction, we need to keep track of them.

  15. Describing Compound Formulas. This section discusses diffent ways to describe and determine the formula of a compound. The first part is on percent composition, if needed review percent calculations. The next discussion is on the difference between emperical and molecular formula. This difference is subtle, but you need to understand it to successfully work several of the homework problems. Read carefully.

  16. Hydrated Compounds. Many compounds are found as hydrates. This section is very closely related to the previous section about molecular formulas.
This page is maintained by
Scott Van Bramer
Department of Chemistry
Widener University
Chester, PA 19013

Please send any comments, corrections, or suggestions to svanbram@science.widener.edu.

This page has been accessed 3235 times since 5/30/97.
Last Updated Friday, May 25, 2001 2:11:17 PM