This document provides instructions for calculating the abundance of different isotopes within an element. It explains key concepts such as atomic mass, isotopes, and using proportions to calculate isotope percentages. As an example, it shows the calculation to find the percentage abundance of carbon-12 isotope. The document also provides sample exam questions and instructions for a student presentation on a given element.

2.  To describe an isotope
 To explain how atomic mass can vary within
one element
 To calculate the abundance of different
isotopes

3.  An element is usually defined by the number
of protons in the nucleus
 If the number of protons changes the element
changes
 The number of protons is equal to the
number of electrons in an atom
 However the number of neutrons can change
between different atoms of the same element

4.  An isotope is a chemical with a different
atomic mass but the same number of protons
as another
 Take carbon as an example

5.  The atomic mass of carbon on the periodic
table is 12.011
 This is the mean mass of carbon on Earth

6.  To calculate the abundance of one isotope it
is important to know the mass of all isotopes
and the mass on the periodic table
 We are going to calculate the % abundance of
carbon 12

7. It is firstly important to understand the concept
of proportions and percentages
Carbon 12 + carbon 14 = 100% of all carbon
We are trying to find the % of 12C so we will call
that x
This means that:
12x + (100-x)14 / 100= 12.011
where x is % carbon 12,
(100-x) is % carbon 14

8. 12x + (100-x)14/100 = 12.011
Multiply out the brackets
12x + 1400-14x /100= 12.011
Multiply by 100 to remove the /100
12x +1400 -14x = 1201.1
Subtract the whole number leaving only x on one side
12x – 14x = -198.9
-2x=-198.9
-x = 99.45
x = 99.45

9.  Research to find an element that has 2
common isotopes
 Calculate the relative abundances of these 2
isotopes – If you find a website that offers
you the information ensure that it is the
correct answer!
 Write out an exam style question and give it
to your neighbour

10. Average atomic mass =
(abundance of isotope 1)(mass of isotope 1) +
(abundance of isotope 2)(mass of isotope 2)

11. Isotope Isotopic mass (u) Isotopic abundance (%)
24Mg 24 78.99
25Mg 25 10.00
26Mg 26 11.01

12. (24)(0.7899)+(25)(0.10)+(16)(0.1101)=
18.9576 + 2.5 + 2.8626 =
24.3202

13.  You will be given an element from the
periodic table
 You will produce a short (3-4 minute)
presentation about that element
 The presentation MUST include the electronic
structure, isotopes of the element, symbol
and position on the periodic table
 It should also include uses of the element,
how it was discovered, impact of uses of the
element (if applicable)

14.  The student explains how science is applied and
how it may be used to address a specific problem
or issue in a local or global context.
 The student discusses the effectiveness of
science and its application in solving the problem
or issue.
 The student discusses and evaluates the
implications of the use and application of science
interacting with at least two of the following
factors: moral, ethical, social, economic, political,
cultural and environmental.

15.  The student uses sufficient scientific
language correctly.
 The student communicates scientific
information effectively.
 When appropriate to the task, the student
fully documents sources of information
correctly.