Atoms and Elements 4
Chapter Overview
Chapter 4 brings us from the earliest recorded ideas on atomic theory over 2000 years
ago up to the present day. This chapter serves as a historical timeline giving the students a better
understanding of the origins of the facts that we assert. The origin of current atomic theory is
presented and the student’s vocabulary is again extended.
Lecture Outline
4.1 Experiencing Atoms at Tiburon
A. Atoms are very small
4.2 Indivisible: The Atomic Theory
Learning Objective: Recognize that all matter is composed of atoms.
A. Democritus (~400 BC)
B. Dalton (early 1800s)
2. All atoms of a given element have the same mass and other properties that
distinguish them from atoms of other elements
4.3 The Nuclear Atom
Learning Objective: Explain how the experiments of Thomson and Rutherford led to the
development of the nuclear theory of the atom.
A. Positive and negative charges (Thomson)
4.4 The Properties of Protons, Neutrons, and Electrons
Learning Objective: Describe the respective properties and charges of electrons, neutrons,
and protons.
A. Masses expressed in atomic mass units (amu)
4. Species of opposite electric charge cancel to make a neutral atom
4.5 Elements: Defined by Their Number of Protons
Learning Objective: Determine the atomic symbol and atomic number for an element
using the periodic table.
A. Identity of atom comes from the number of protons
B. Atomic number (Z) = number of protons
C. Chemical symbol is a shorthand notation of chemical name
4.6 Looking for Patterns: The Periodic Law and the Periodic Table
Learning Objective: Use the periodic table to classify elements by group.
A. Mendeleev (1834 ─ 1907)
B. Periodic law
1. Group 1 – alkali metals
3. Group 7 – halogens
4.7 Ions: Losing and Gaining Electrons
Learning Objective: Determine ion charge from numbers of protons and electrons.
Learning Objective: Determine the number of protons and electrons in an ion.
A. If an atom has different numbers of protons and electrons it is an ion
B. Cation = positive ion
C. Anion = negative ion
4.8 Isotopes: When the Number of Neutrons Varies
Learning Objective: Determine atomic numbers, mass numbers, and isotope symbols for
an isotope.
Learning Objective: Determine number of protons and neutrons from isotope symbols.
A. Isotopes have the same chemical properties, but different masses
4.9 Atomic Mass: The Average Mass of an Element’s Atoms
Learning Objective: Calculate atomic mass from percent natural abundances and isotopic
masses.
A. Value on periodic table represents average mass of all isotopes
B. No chlorine atom weighs exactly 35.453 amu
Chemical Principle Teaching Ideas
The Atomic Theory
Many students believe that we have completely understood current atomic theory for
centuries. They do not understand that the concepts we now hold as truth became “mainstream”
200 years ago, with many changes occurring since. Providing a brief history of atomic theory,
Charge
Most students understand the concept of electrical charge, but a simple demonstration of
static electricity will reinforce the idea.
The Periodic Table
The periodic table can be the best exam “cheat sheet” a student could ever use. By
understanding the layout of the table, many trends and quite a lot of information can be
extracted. Mentioning briefly the things that have periodic trends will also reinforce the periodic
law in their minds.
Atomic Number, Ions, and Isotopes
Emphasize that all atoms having the same number of protons behave the same chemically
Skill Builder Solutions
4.1. a. Located in Group 1A, sodium is atom #11.
4.2. a. Sulfur is in Group 6A and is a nonmetal.
4.3. a. Group 1A is called the alkali metal group.
b. Group 3A has no special name.
4.4. a. Nickel has 28 protons, so the net charge is 28 – 26 = +2.
b. Bromine has 35 protons, so the ion charge = 35 – 36 = -1.
c. Phosphorus has 15 protons, so the ion charge = 15 – 18 = -3.
Guided Inquiry Ideas
Below are a few example questions that students answer in the guided inquiry activities provided
in the Guided Activity Workbook.
If an atom has a net charge of zero, what could you conclude about the relative number of
electrons and protons? Explain.
Rutherford’s gold foil experiment showed that practically all the mass is concentrated in a very
small location called the nucleus. Which particles must be in the nucleus?
A mad scientist proposes that Type 2 carbon has more protons. How would you respond?
How many electrons would you need to weigh the same as one proton?