PACT Due Dates

Atomic structure and isotopes (Eric Boyer)

Atomic structure and isotopes

student data

7. The organization of the Periodic Table is based on the properties of the elements and reflects the structure of atoms.
    b. elements are defined by the number of protons in the nucleus, which is called the atomic number. Different isotopes of an                element have a different number of neutrons in the nucleus.


10 petri dishes (per group if possible)
14 regular-sized boxes of Tic Tacs (7 of each color), or 6-8 of the large boxes (3-4 of each)
Periodic table
labeling markers


The purpose of these two labs is to introduce the students to the structure of the atom, and the makeup of the nucleus in particular.  Students will be introduced to the periodic table, including atomic number and atomic mass.  Prior to the first lab, students should know the location and charge of protons and neutrons.

Procedure (Lab 1)

1.  The student will count the number of white Tic Tacs (protons) and orange Tic Tacs (neutrons).
2.  Calculate the atomic mass for each of the unknown elements
3.  Identify the element using the periodic table.

Preparation for Lab 2

Three sets of three isotopes
9 petri dishes
Two different colors of Tic Tacs
Labeling marker

Unlike the first lab, there is no introduction to this lab.  It should simply be introduced as a counting exercise.  Shortly after starting the exercise, some students will complain that some of the dishes have the same number of white Tic Tacs.  They should count them again to make sure.  When they get the same count, ask them if there is anything different about the unknowns, this should clear up some of the confusion.


1.  What determines the identity of the element?
2.  What is the difference between isotopes of a given element?  Does this effect how they behave chemically?
3.  Why do elements on the periodic table have such odd masses?
4.  What does it mean when we say an element is radioactive?

Norman Herr,
Apr 14, 2011, 12:40 AM
Norman Herr,
Apr 14, 2011, 12:29 AM