Nuclear Chemistry

1991 DBy:

Stephanie Chenand

Stephanie Ng

1991 D

Explain each of the following in terms of nuclear models.

1991 D (a)

The mass of an atom of the is less than the sum of the masses of two protons, two

neutrons, and two electrons.

4He

1991 D (a) ANSWER

The mass of an atom of is less than the sum of the masses of two protons, two

neutrons, and two electrons because of the “Binding Energy.” Binding energy is the

energy which is used to hold the nucleus and atom together. This is the mass defect.

4He

1991 D (b)

Alpha radiation penetrates a much shorter distance into a piece of material than does

beta radiation of the same energy.

1991 D (b) ANSWER

Alpha radiation penetrates a much shorter distance into a piece of material that does beta radiation of the same energy because of the size. Since beta radiation is using the electron, its size of being 1/2000 of an atom is very tiny. Yet, since a atom is much larger than an electron, it is more difficult

for alpha radiation ( ) to go farther.

4He2

4He2

1991 D (c)

Products from a nuclear fission of a uranium atom such as 90Sr and 137Ce are highly radioactive and decay by emission of beta

particles.

1991 D (c) ANSWERSince radioactivity is based on the belt of stability,

we must calculate the ratio between the protons and neutrons.

neutrons / protons = (90 – 34) / 34 = 1.647 neutrons / protons = (137 – 58) / 58 = 1.362The ratio of protons to neutrons is much higher than

the ideal 1 : 1 ratio. Hence, are highly radioactive and decay by emission of beta particles in which the neutrons into protons for stabilization.

90Se137Ce

90Se 137Ce

1991 D (d)

Nuclear fusion requires large amounts of energy and to get started, whereas nuclear fission can occur spontaneously, although

both processes release energy.

1991 D (d) ANSWERNuclear fusion requires large amounts of energy

because of the high level of temperature the reaction must undergo in order for it to work. Yet nuclear fission can occur spontaneously despite

the fact that both processes release energy, because it is considered a “chain reaction”.

Fission begins whenever a neutron is bombarded into an atom, releasing more neutrons and atoms,

continuously hitting each other and maintaining the process of fission.