Tuesday, October 24, 2006


Lesson Title: Isotopes

Learning Outcome:At the end of the sessions, you must be able to define isotopes, cite the relationship between atomic mass and the relative abundance of isotope identify the use of some radioactive elements/isotopes

Learning Presentation:

What is an isotope? click here to find out you can also check you text books its on page 64-65 :)

or play this video for better understanding

From our previous lessons the atomic mass is the number of protons plus the number of neutrons but why are the mass in the periodic table of elements not in whole number is it because of the electrons?

The answer is no, it is not in whole numbers because it is the average mass of the isotopes present of that element to know how to calculate click here

1. The protons and neutrons are particles of the nucleus. The American physicist A. J. Dempster and the English chemist F. W. Anston (1914) found out that some elements have atoms with different atomic masses. These are called isotopes of the element. Atoms of the same element would have the same atomic number. The atomic mass of isotopes varies because they have different numbers of neutrons. Atomic mass is given by the sum of the masses of p+ and no present in the atom. Mass number is rounded off for convenience

1. The variation in the number of neutrons does not change the identity and therefore, the properties of an element. It is atomic number or the number of protons that identifies an element.

2. Atomic mass is generally, not a whole number. It is the weighted average of the masses of isotopes of a particular element. The percentage of isotopes of a particular element. The percentage abundance of each isotope is taken into account.

3. Isotopes are classified as stable and unstable.
a. Stable isotopes do not exhibit radioactivity, which explains why they exist and persist in nature. Many elements that occur naturally and abundantly on earth are stable isotopes. 16O and 12C are examples.

b. Unstable isotopes exhibit radioactivity (tremendous emission of invisible rays due to the splitting of the nucleus of an atom) and thus, are known as radioisotopes.

4. Using the unstable isotopes/radioisotopes
a. Dating fossils and rocks - Geologists use radioactive decay rates to tell the ages of rocks and fossils. Uranium –238 is used to determine the age of rocks. It takes 4.5 x 109 years for half of the sample of U-238 to decay.

b. Radiocarbon dating - This method is used to determine the ages of materials, which were once living. It is based on the decay rate of carbon-14. Living organisms contain an almost fixed amount of carbon-14 per unit mass. When the organisms die, C-14 starts to decay according to the rate law. The half-life of C-14 is 5730 years.

c. Medical uses - Radioisotopes are used to detect and treat abnormalities in the body.

Activity: click here to practice on a game

Application/ Valuing Assignment:
Answer the following by posting your answer or write on a piece of paper you will be graded based on the following
1. Give 2 or 3 examples of elements with isotopes which isotope is beneficial and how and which are not beneficial and why?
2. What is the impact of isotopes to our lives?
3. What are the biological effects of radiation?
4. What is the difference between natural and artificial radioactivity?
5. Can both be utilized to be beneficial to man?

Monday, October 16, 2006

atomic structure

Lesson Title: Sub-atomic particles

Learning Outcome:

At the end of this your should be able to know the different sub-atomic particles of an atom, what is an isotope and compute for the number of sub-atomic particles provided with a given.

As i have discussed earlier the atom was the smallest indivisible unit of matter it, this was first coined by democritus, and refined by Dalton. But the discovery of Thomson, Rutherford, Chadwick, and Goldstein has made us think otherwise. The atom is no longer a solid sphere but it is made up of several componets the protons, neutrons and electrons.

To learn more about this sub-particles click here.

Computing for the number of protons, electrons and neutrons as well as the atomic number and mass can be a daunting task, but follow this link and you will understand better.

Test your understanding click here

Sometimes elements vary in mass number they are called isotopes

How will you know the identity of the atom?
Is it possible for an atom of the different element to have the same number of electron and neutron? click here to answer or submit in 1 whole paper unique answer is required you will be graded as the following