Chapter 4: Atoms and Elements
Date:____________
Section 6: Isotopes - Notes
Objectives:
 Determine atomic numbers, mass numbers, and isotope symbols for an isotope.
 Determine number of protons and neutrons from isotope symbols.
 Calculate atomic mass from percent natural abundances and isotopic masses.
Isotopes:
 ________________________________________ assumed that all of the atoms of a given
element were identical.

________________________________________ discovered that nuclei of most atoms contain
neutrons as well as protons.

All atoms of a given element have the same number of _______________________.
o

They do not necessarily have the same number of _______________________.
Atoms with the same number of protons but different numbers of neutrons are called
__________________________
o
All elements have their own unique __________________________________________
of isotopes.

Naturally occurring neon contains three different
isotopes:
o
Ne-20 (with _____ protons and _____ neutrons)
o
Ne-21 (with _____ protons and _____ neutrons)
o
Ne-22 (with _____ protons and _____ neutrons)
Isotope Notation:
 Isotopes are often symbolized in the following way:

o
_____ = element symbol
o
_____ = Atomic Number: number of protons
o
_____ = Mass Number: sum of the number of protons and neutrons
For example, the symbols for the isotopes of neon are as follows:

The ___________________________ (A) is the sum of the number of protons and the number
of neutrons.
o
The number of ________________________ in an isotope is the difference between the
mass number and the atomic number.

A second notation for isotopes is the chemical symbol (or chemical name) followed by a hyphen
and the mass number of the isotope.


In this notation, the neon isotopes are as follows:
o
Ne-20 ___________________________
o
Ne-21 ___________________________
o
Ne-22 ___________________________
Practice:
o
Give the number of protons, neutrons, and electrons in the following atom:
o
Write the symbol for the magnesium-24. How many electrons and neutrons does this
atom have?
o
Write the symbol for the silver atom (Z = 47) that has 61 neutrons.
o
What are the atomic number (Z), mass number (A), and symbols of the carbon isotope
that has 7 neutrons?
o
How many protons and neutrons are in chromium-52?
Average Atomic Mass:
 In nature, elements are usually found as a ___________________________________________.

The atomic mass of each element listed in the periodic table represents the
______________________________ of the atoms that compose that element.

Naturally occurring chlorine consists of:
o
__________________ chlorine-35 (mass 34.97 amu)
o
__________________ chlorine-37 (mass 36.97 amu)

Its atomic mass is the following:

In general, atomic mass is calculated according to the following equation:
o
Atomic mass = (Percent of isotope 1 × Mass of isotope 1) + (Percent of isotope 2 × Mass
of isotope 2) + (Percent of isotope 3 × Mass of isotope 3) + …

where the percents of each isotope are converted to their _________________
values

Practice:
o Gallium has two naturally occurring isotopes:

Ga-69, with mass 68.9256 amu and a natural abundance of 60.11%

Ga-71, with mass 70.9247 amu and a natural abundance of 39.89%.
o
Calculate the atomic mass of gallium.
o
Magnesium has three naturally occurring isotopes with masses of 23.99, 24.99, and
25.98 amu and natural abundances of 78.99%, 10.00%, and 11.01%. Calculate the
atomic mass of magnesium.
Nuclear Radiation:
 The nuclei of some isotopes of a given element are _____________________________.
o
Usually happens with atoms that have a _____________________________________ of
protons and neutrons.

These atoms emit a few __________________________________________________________
from their nuclei and change into different isotopes of different __________________________.

The emitted subatomic particles are called ____________________
______________________.

The isotopes that emit them are termed ____________________________.

Nuclear radiation can be harmful to humans and other living organisms because the energetic
particles interact with and __________________________ biological molecules.

Some isotopes, such as ________________, emit significant amounts of radiation only for a very
short time.

Other isotopes, such as ________________, remain radioactive for a long time - thousands,
millions, or even billions of years.

Radioactive isotopes are not always harmful; many have ___________________________ uses.
o
For example, ___________________________ (Tc-99) is often given to patients to
diagnose disease.

The radiation emitted by Tc-99 helps doctors image internal organs or detect
infection.