Can some one please help me wit a few Chemistry questions???

Question

Isotopes of a given element have many different properties, such as mass, but the same chemical properties. Why is this?

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2. What is the binding energy per nucleon of Au-197 (atomic mass = 3.2696 x 10-25kg)?

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3. If there are 128 neutrons in Pb-210, how many neutrons are found in the nucleus of Pb-206?

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4. The beta emission process results in the daughter nucleus differing in what manner from the parent?

A. atomic mass increases by one

B. atomic mass decreases by two

C. atomic number increases by one

D. atomic number decreases by two.

5. The alpha emission process results in the daughter nucleus differing in what manner from the parent?

A. atomic mass increases by one

B. atomic mass decreases by two

C. atomic number increases by one

D. atomic number decreases by two.

6. Of the main types of radiation emitted from naturally radioactive isotopes, which is the most penetrating?

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7. When bismuth-214 emits a positron, the remaining daughter nucleus is which of the following?

A. lead-214

B. actinium-215

C. polonium-214

D. bismuth-215

8. What is the isotope formed when 232 90 Th undergoes alpha decay?

A. 42He

B. 22888Ra

C. 23086Rn

D. 24He

Answer 1

1.  Chemical properties have almost nothing to do with mass and almost everything to do with charge.  Thus, while isotopes of a given element differ in their mass, they all carry the same number of protons and electrons, meaning their ability to react will be the same as well.

2.  Nuclear binding energy is calculated by taking the difference between the measured atomic mass (given) and the masses of the protons and neutrons added as separate entities and then multiplying this difference by c^2.  Thus:

(mass of one proton) * (atomic number) + (mass of one neutron) * (mass number - atomic number) = mass of all nucleons

(1.67262 x 10^-27 kg)*(79) + (1.67492 x 10^-27 kg)(118) = 3.2978 x 10^-25 kg

(3.2978 x 10^-25 kg) - (3.2696 x 10-25 kg) = 2.8175 x 10^-27 kg  (mass difference)

(2.8175 x 10^-27 kg)(299792458 m/s)^2 = 2.5322 x 10^-10 joules OR 1.5805 x 10^9 electron volts (eV) (total nuclear binding energy)

We then take this binding energy and divide by the number of nucleons, which is equal to the mass number.  Thus:

(1.5805 x 10^9 eV) / 197 nucleons = 8.0230 MeV per nucleon

3.  Since both are isotopes are lead, the difference in mass number is a difference only in neutron number.  Thus Pb-206 has 124 neutrons

4.  Beta emission first involves the conversion of a neutron into a proton plus an electron.  The electron is then emitted from the nucleus, but the proton stays.  Thus the mass number stays the same, but the atomic number goes up by 1.

5.  Alpha decay involves the loss of a He-4 atom from the parent atom.  Since He-4 contains 2 protons and 2 neutrons, the mass number decreases by 4 while the atomic number decreases by 2.

6.  The three main types are alpha, beta, and gamma.  Alpha involves a relatively large particle emission, and thus it is blocked relatively easily (a piece of paper will do the trick).  Beta emission involves a relatively small particle (only an electron or a positron), so it can penetrate much further (this is where you start needing good shielding).  The gamma particle is actually not a particle at all, but is instead a quantum of high-energy light (in the X-Ray range), and thus it can penetrate the furthest (unless you have a lead barrier between you and the gamma source)

7.  A positron is a particle with the mass of an electron but with a charge of +1 instead of -1.  To create this, energy strikes a proton, converting it into a positron plus a neutron.  The positron is emitted, but the neutron stays in the nucleus.  For the nucleus, then, a positron is consumed to make a neutron, thus the atomic number decreases while the mass number stays the same, giving you lead-214.

8.  As above, alpha decay involves the loss of 4 2 He.  Thus subtract 4 from 232 and 2 from 90 to get 228 88 Ra.