Do the proton and the neutron have exactly the same mass? How do the masses of the proton and the neutron compare to the mass of the electron? Which particles make the greatest contribution W the mass of an atom? Which particles make the greatest contribution to the chemical properties of an atom?

2.86 For some uses, the relative abundance of isotopes must be manipulated. For example, a medical technique called boron neutron capture therapy needs a higher fraction of 10B than occurs naturally to achieve its best efficiency. What would happen to the atomic weight of a sample of boron that had been enriched in 10B? Explain your answer in terms of the concept of a weighted average.

It is good practice to actively read the textbook and to try to verify claims that are made when you can. The following claim is made in your textbook: “. . . if the nucleus were the size of a grape, the electrons would be about 1 mile away on average.” Provide mathematical support for this statement.

Though the common isotope of aluminum has a mass number of 27, isotopes of aluminum have been isolated (or prepared in nuclear reactors) with mass numbers of 24, 25, 26, 28, 29, and 30. How many neutrons are present in each of these isotopes? Why are they all considered aluminum atoms, even though they differ greatly in mass? Write the atomic symbol for each isotope.

What particles are found in the nucleus of an atom? What is the charge of the nucleus?

How many platinum atoms are in a pure platinum ring weighing 4.32 g?

Read the Chemistry in Focus” segment “Whair”Do You Live? How can isotopes he used to identify the general region of a person’s place of residence?

An average atomic nucleus has a diameter of about m.

2.19 Naturally occurring uranium consists of two isotopes, whose masses and abundances are shown below: Only 235U can be used as fuel in a nuclear reactor, so uramium for use in the nuclear industry must be enriched in this isotope. If a sample of enriched uranium has an atomic weight of 235.684 amu, what percentage of 235LT is present?