# Atomic Mass of Silver

### Research Questions:

• What is atomic mass? How does it differ from relative atomic mass?
• How can atomic mass be calculated?
• How does atomic mass differ from atomic weight?
• Is it possible for an element to have different atomic masses? Why?
• What percent of uranium is radioactive?

Students often confuse atomic number, atomic mass, atomic weight and relative atomic mass. The following definitions may be helpful:

Atomic number is the number of protons in an element. This number is always the same for every atom of a particular element; it is a fundamental property of the element.

Atomic mass is the total mass of protons, electrons and neutrons in an atom. Unlike atomic number, atomic mass is not a fundamental property of an element; rather, it is a fundamental property of a particular isotope.

An isotope is a particular form of an element. While all isotopes have the same number of protons, the number of neutrons can vary. For example, hydrogen has three isotopes: protium (with 0 neutrons), deuterium (with 1 neutron) and tritium (with 3 neutrons).

Atomic weight is the ratio of the average mass of atoms of a particular element to 1/12 the mass of an atom of carbon-12. While different samples of a particular element may have slightly different atomic weights, this number is sufficiently important that it appears on the periodic chart.

Relative atomic mass is a synonym for atomic weight. It represents the average of the mass of all isotopes weighted by the abundance of each isotope.

### Materials:

This “paper-and-pen” experiment does not require setting up any special apparatus. All that is needed is a periodic table.

### Experimental Procedure:

Relative Atomic Mass of Silver

1. The formula for relative atomic mass is the relative abundance over 100 divided by the isotope number. This can be expressed as:

(A/100 • a) + (B/100 • b) + (C/100 • c)…. = relative atomic mass

A, B, C stand for different relative abundances of isotope numbers a, b and c.

Silver has two isotopes, silver 107 and silver 109. The relative abundance of these is 51.84 % and 48.16 % respectively.

Calculate the relative atomic mass of silver.

Relative Atomic Mass of Uranium

1. Uranium has three isotopes: U 234, U235 and U238. The relative abundance of these is 0.01%, 0.71% and 99.27 % respectively. Use this information to calculate the relative atomic mass of uranium.

Relative Atomic Mass of Barium

1. There are seven different isotopes of barium. Doing on-line research, find out what these are and their relative abundance. Use this information to calculate the relative atomic mass of barium.

Terms/Concepts:  Atomic number; Atomic mass; Atomic weight; Isotope; Relative atomic mass

References:

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