NAME ______
Atomic Structure / PERIOD ______DATE ______
Isotope Abundance / LAB PARTNERS ______
______

BACKGROUND

According to Dalton’s atomic hypothesis, all atoms of the same element are identical. This notion of the atoms, however, is somewhat outdated, as not all atoms of the same element possess the same number of neutrons (possess a different atomic mass). It is in this spirit, a cavity-producing form of torture, involving candy, has been selected for you.

J.J. Thomson was the first to note that atoms of an element can have different masses but behave chemically the same. His student, F.W. Aston, developed the mass spectrometer and studied these atoms. These atoms are called isotopes. They have the same number of protons, but a different mass due to a varying number of neutrons. These isotopes can occur in different percents in nature. The average atomic mass is determine by multiplying the abundance (percent) of the isotope as found in nature by the mass of that isotope for each isotope and then adding these results.

(%X1).(massX1) + (%X2).(massX2) + (%X3).(massX3) + (etc)
= average atomic mass

OBJECTIVES

·  To demonstrate how isotope abundance and exact mass is used to determine average atomic mass

MATERIALS

ICP Lab (page 1 of 2)

·  M&M’s

·  Calculator

·  Graph Paper

ICP Lab (page 1 of 2)

SAFETY PRECAUTIONS

·  5-Second Rule

PROCEDURE

1.  Pour a small bag of M&M’s on the paper towel on the desktop. Start by counting each color. Each color represents an isotope of the same element, Candium. Determine the isotopic abundance of each isotope (how many of each color are there?).

2.  Given below are the exact masses of each isotope in CMUs (Candy Mass Unit).

Isotope / Red / Green / Brown / Orange / Yellow / Blue / Purple
Exact Mass (CMU) / 29 / 30 / 31 / 32 / 33 / 34 / 35


ANALYZING DATA (Show you work in the space provided)

1.  Determine the percent, to the nearest tenth, of each "M&M isotope" in your bag?

% Color = (# of Color/Total M&M’s) x 100

2.  Which isotope is most abundant?

3.  Create a bar graph to represent the percent of each "M&M isotope" in your bag.

4.  Calculate the average atomic mass of the "M&M atom" in your bag?

{[(% Red) x (29)] + [(% Green) x (30)] + [(% Brown) x (31)] +
[(% Orange) x (32)] + [(% Yellow) x (33)] + [(% Blue) x (34)] +
[(% Purple) x (35)]} /100 = average atomic mass

5.  How is the value you calculated analogous to the average atomic masses found on the periodic table?

6.  Hydrogen has three naturally occurring isotopes which figure into the average atomic mass found on the periodic table (1.00974): hydrogen-1, hydrogen-2, and hydrogen-3. Which would you guess is most abundant? Explain your answer.

ICP Lab (page 1 of 2)