Ch 2 Part 1
Supplemental Instruction
Iowa State University / Leader: / Kia
Course: / CHEM 177
Instructor: / Dutton
Date: / 8/31/17

Warm up – try without looking at your notes!

Fill in the blanks of atomic theory

  1. Each element consists of tiny, indestructible particles called ______
  1. All atoms of an element are ______, and they are ______from the atoms of any other element
  1. Atoms combine in simple ratios of ______numbers to form compounds
  1. Atoms are not ______, ______, or ______in chemical reactions. The reaction only changes the arrangement in which the atoms are bound

Label the following groups on the provided periodic table

·  Alkali Metals

·  Alkali Earth metals

·  Transition metals

·  Halogens

·  Metalloids

·  Lanthanides*

·  Noble Gases

·  Actinides*

*indicates a section of the periodic table not mentioned yet in class but you should know (hint – what elements to this names resemble?)

Practice Problems

1.  Fill in the following tables (assume no charge)

Symbol / 27Al
Number of Protons / 42 / 92
Number of neutrons / 56
Number of electrons / 60
Mass Number / 143 / 238

2.  What is the atomic weight of antimony if it has only two naturally occurring isotopes, Sb-121 with an isotopic mass of 120.904 amu and an abundance of 57.21% and Sb-123 with an isotopic mass of 122.904 amu and an abundance of 42.79%?

3.  (EOC 2.27) The 1997 mission to Mars included a small robot, the Sojourner, that analyzed the composition of Martian rocks. Magnesium oxide from a boulder dubbed “Barnacle Bill” was analyzed and found to have the following isotopic composition:

Mass (amu) / Natural Abundance (%)
39.9872 / 78.70
40.9886 / 10.13
41.9846 / 11.17

If essentially all of the oxygen in the Martian MgO sample is oxygen-16 (which has an exact mass of 15.9948 amu), is the average atomic mass of magnesium on Mars the same as on Earth (24.31 amu)?

4.  (EOC 2.30) Use the following table of abundances and masses of the three naturally occurring argon isotopes to calculate the mass of Argon-40

Symbol / Mass (amu) / Natural Abundance (%)
36Ar / 35.96755 / 0.337
38Ar / 37.96272 / 0.063
40Ar / ? / 99.60
Average / 39.948

Challenge Question

5.  Bromine has two naturally occurring isotopes: Br-79 (78.918 amu) and Br-81 (80.916 amu). The atomic weight of Br is 79.904 amu. What are the fractional abundances of Br-79 and Br-81? Check your answer by comparing the atomic weight with the weight of the isotopes.