Chemistry B 4 Nuclear Chemistry

Front 1

What is nuclear chemistry?

Back 1

-Nuclear chemistry is the study of nuclear reactions. It is a subfield of chemistry dealing with radioactivity, nuclear processes/properties.

-The study of radioactive elements.

Front 2

What holds protons and neutrons together?

Back 2

-Protons and neutrons are held together by the Strong Nuclear Force (aka ¨strong force¨).

-Strong nuclear force is one of the four basic forces in nature (others are gravity, electromagnetic force, and weak nuclear force).

Front 3

How does the strong nuclear force bring stability?

Back 3

Protons repel each other, the strong nuclear forces can overpower this, and keep the nucleus together.

Front 4

How does the strong nuclear force work?

Back 4

-Strong nuclear force operates at very small distances

-It holds protons and neutrons together with the force 100x greater than proton-proton repulsion.

-Because protons repel each other, the nucleus needs a certain proton/neutron ratio.

Front 5

What is one of the important factors that decides whether a nucleus is stable or not?

Back 5

-An important factor is whether or not the nucleus falls within the belt of stability.

-The belt of stability shows the amount of neutrons needed for the amount of protons, and remain stable.

-Eventually a 1:1 ratio becomes unstable (decomposes)

Front 6

As a nucleus gets more protons, how are neutrons effected?

Back 6

As the nucleus gets more protons, more neutrons are needed to remain stable.

Front 7

What are the two rules of thumb for nuclear stability?

Back 7

1) least stable nuclei tend to be those with an odd number of protons/neutrons.

2) Isotopes with specific numbers tend to be more stable than the rest. These are: 2, 8, 20, 28, 50, 82, 126.

Front 8

What happens to nuclei that fall outside the belt of stability?

Back 8

If a nucleus falls outside the belt of stability, it undergoes radioactivity, which is the process of emitting particles, giving the nuclei a favourable neutron-proton ratio (nuclear decay).

Front 9

What is alpha decay?

Back 9

-Alpha decay is the process which nuclei lose alpha particles (a helium nucleus) to become more stable.

-Occurs when a nucleus has more than 83 protons.

Front 10

What is beta decay?

Back 10

-Beta decay is the loss of a beta particle (high energy electron)

-This happens when a nucleus has too many neutrons (above the belt)

Front 11

What is gamma decay?

Back 11

-Gamma decay is when a nucleus emitts a high energy gamma ray.

-Gamma rays are the most energetic photon of electromagnetic radiation. Short wavelength, less than one-tenth of a nanometer.

-Gamma rays often accompany either alpha or beta radiation.

-Gamma radiation involves transitions between energy levels within the nucleus.

Front 12

What is positron emission?

Back 12

-Positron emission is the loss of a positron, the opposite of an electron (same mass, positive charge).

-This happens below the belt of stability.

Front 13

What is electron capture (K-capture)?

Back 13

-Electron capture is the addition of an electron to a proton in the nucleus.

-As a result, a proton is transformed into a neutron.

p+ + e- -> n

-This happens below the belt of stability.

Front 14

What is neutron emission?

Back 14

-The emission of a neutron

-This does not change the atomic number

-Extremely unstable nucleus decays via neutron emission

Front 15

What is the maximum amount of protons a nucleus can have before it is unstable?

Back 15

No stable nucleus can have any more than 83 protons.

Front 16

How is radioactivity measured?

Back 16

-Radioactivity is measured by the number of disintegration that a sample undergoes per second.

-Units is becquerel (bq)

1 becquerel is 1 disintegration per second.

A= kN

A - number of decays over time

N - number of radioactive nuclei

k - decay constant

Front 17

What is the law of radioactive decay?

Back 17

-All radioactive decay processes are a first order reaction.

activity= - (ΔN/Δt) = kN

ln([N]t/[N]0) = -kt

ΔN - change in the number of radioactive nuclei

Δt - time interval which change occurs

N - the number of radioactive nuclei

K - decay constant

Front 18

Does a more stable element have a faster or slower half life?

Back 18

A more stable element has a slower half life.

Front 19

What is radiological dating?

Back 19

-Radiological dating is determining the age of a geological or archaeological discovery.

-Based on the premise that the half-lives of radionuclides are constant.

Front 20

What is carbon dating?

Back 20

-Carbon dating is used to estimate the age of organic remains

- ¹⁴C undergoes beta decay, t1/2 5715 years.

- ¹⁴C:¹²C are constant when a plant or animal is alive.

-At death, ¹⁴C is at its maximum then undergoes beta decay.

-The ratio between ¹⁴C and ¹²C in a sample is measured.

The formula is ln(r0/r1) = (1.21x10⁻⁴yr⁻¹) t

r0 - ¹⁴C:¹²C ratio at time of death

r1 - ¹⁴C:¹²C ratio now

t - age of sample in years

Front 21

What is nuclear transmutation?

Back 21

-Nuclear transmutation is changing one element into another by natural alpha and beta decay, or by bombardment of nuclei with high energy particles.

Front 22

What is nuclear binding energy?

Back 22

-A tremendous amount of energy stored in a nuclei.

-As a result, the mass of a nucleus is always less than the combined mass of individual particles that make it up.

Front 23

What is nuclear fission?

Back 23

-Nuclear fission is when a nucleus splits into roughly two equal parts after it captures a slow neutron.

-This starts a chain reaction and the nuclei keep splitting

-This often creates free neutrons and photons (in form of gamma rays), and releases a very large amount of energy.

Front 24

What is a critical mass and supercritical mass?

Back 24

-Critical mass is the mass needed to maintain the constant rate of chain reaction. This is used to control the reaction.

-Supercritical mass is excess the critical mass. Reaching supercritical mass can cause the reaction to get out of control.