CHEMISTRY 1Nuclear Chemistry

Chapter 28

NUCLEAR CHEMISTRY

1896- Antoine Becquerel discovered ___________________

He accidently left uranium ore on top of photographic plates. They became fogged from the exposure. Becquerel had 2 graduate students: _______________ _______________

radioactivity

Marie &Pierre Curie

_______________________- the property by which uranium gives off rays

______________________-penetrating rays emitted by a radioactive source.

In 1903, the Curies and Becquerel won Nobel prizes for this discovery.

Radioactivity

Radiation

Types of Radiation 1. Alpha emission -helium nuclei emitted from a

radioactive source 2 protons & 2 neutrons 2+ charge Symbol is Don’t travel far and are not very penetrating Stopped by a sheet of paper Can’t penetrate skin, but dangerous if ingested Very common with heavy nuclides

24

He

Write this

Alpha Decay (α)

Lose 2 protons (+2 charge) & 2 neutrons

He42

Examples:

U ___ + He23490

42

Ra Rn + He 24

88226 222

86

23892 Th

Law of conservation of mass

Atomic #

Mass # = # protons + # neutrons

226 88

42

222 86

Ra Rn + He

Atomic # 88 86 + 2

Mass # 226 222 + 4

2. Beta emission - fast moving ___________ formed by the decomposition of a neutron of an atom. The neutron breaks into a proton and an electron. The proton stays in the nucleus and the electron is ejected. (net effect: neutron changes into proton) Write this:

n H + e01 1

1 10

electrons

Much smaller than alpha particles Symbol is Charge is -1 Much more penetrating than alpha particles Stopped by aluminum foil or thin pieces of

wood

10C N + e 6

14714

10

eWrite this

Beta Decay (β)

Lose electron (-1 charge, no mass)

β 0-1

C N + β14 6

14 7

0-1

3. Gamma emission - _________________ _____________ (high energy) emitted from a nucleus as it changes from an excited state to a ground energy state. Often emitted along with or radiation Symbol is Has no mass & no charge High energy photon

U He + Th + 2 92238 4

223490

electromagneticradiation

the emission of gamma rays is one way that a nucleus with excess energy (in an excited nuclear state) can relax to its ground state

Extremely penetrating, very dangerous Stopped somewhat by several feet of concrete or

several inches of lead

Gamma Emission (γ)

γ00

No mass, no charge, loses just energy

4. Positron emission- ___________________________________ e Antimatter Net effect: changes proton to a neutron Occurs when neutron/proton ratio is too small

1022

01

01 Na e + Ne 11

22

Particle with the mass of an electron but a positive charge

Write this (the 0 and the +1)

Alpha radiation cannot penetrate the skin and can be blocked out by a sheet of paper, but is dangerous in the lung.

Beta radiation can penetrate into the body but can be blocked out by a sheet of aluminum foil.

Gamma radiation can go right through the body and requires several centimeters of lead or concrete, or a meter or so of water, to block it.

Nuclear Transformation (Transmutation)- ____________________________________ bombarding with alpha particles

Bombarding with neutrons

N + He O + H 147

42

178

11

U + n U 23892

10

23992

Changing one element into another

Write these

Fill in the blanks (not in your notes):

1. Co Ni + ____

2. Am Np + ____

3. Th He + ____

4. N + ____ C + H

6027

6026

0 1

241 95

237 93

42

11

14 6

14 7

230 90

42

226 88 Ra

10 n

He

e

Half-life (t1/2)

the time required for ½ of the atoms of a radioisotope to emit radiation and decay to products

the longer the half-life, the more _____________ the isotope

varies from fractions of a second to millions of years

stable

Examples Nitrogen-13 decays to carbon-13 with a half-

life of 10 minutes. How long is 4 half lives?

4 half lives X 10 min/half life =

40 min.

If you start with 2.00 g of nitrogen-13 how many grams will remain after 4 half lives?

2.00 g 1.00 g 0.500 g 0.250 g

0.125 g

4

321

Phosphorous-32 has a half-life of 14.3 yr. How many grams remain after 57.2 yr from a 4.0 g sample?

57.2 yr

14.3yr / half-life= 4 half-lives

4.0 g 2.0 g 1.0 g 0.50 g321

0.25 g4

Carbon-14 dating

Carbon-14 is continuously produced in the ____________ when high energy neutrons from outer space collide with nitrogen-14 in the air.

N + n C + H 147

10

146

11

atmosphere

Carbon-14 combines with oxygen to form CO2 which is incorporated into plant materials. As long as the plant or animal is alive, decaying carbon-14 is continuously replaced. After death, the carbon-14 decays at a steady rate. Carbon-14 decays to Nitrogen-14

C e + N 146

01

147

The proportion of carbon-14 in the atmosphere is relatively constant. The carbon-14/carbon-12 ratio is used to identify the age of wood, cloth and other ______________ artifacts. The half-life of carbon-14 is _______________ years.

Only works for organic materials Adjusted for change in % C-14 over the years

organic5730

Example

If the C-14 in a fossil sample is only 1/4 what it is in living organisms, how old is the object?

To have ¼ remaining, 2 half lives have passed.

2 X 5730 yr =

11,460 yr.

Fission - splitting a heavy nucleus into two nuclei with smaller mass numbers.

used for _____________________

production of ______________causes a chain reaction (which must be controlled)

1 kg of uranium-235 is equivalent to 20,000 tons of dynamite

nuclear energy

n + U Ba + Kr + 3 n 10

23592

14256

9136

10

neutrons

Fission – splitting of atoms.FISSION: splitting of atoms

Fission in a nuclear reactor is carefully controlled. Much of the energy is _______. This energy is used to produce _________ and subsequently, __________________.

A _________________(usually water) is needed. The water (or carbon) also acts as a moderator. It

_____________the neutrons down so that they can be captured by the U-235 fuel.

Control rods made of _______________ are present to absorb excess neutrons to slow down the reaction. They can be raised or lowered into the reactor core.

heatsteam

electricitycoolant

slows

cadmium

Fusion- combining two light nuclei to form a heavier, more stable nucleus

stars produce their energy this way Currently __________________ are

necessary in order to initiate fusion possible future energy source

high temperatures

4 H + 2e He + energy 11

10 2

4

Fusion – two nuclei combine to form a heavier nucleus.

FUSION: two nuclei combine to form a heavier nuclei

Proton-proton chain reaction

Fusion reaction in our Sun’s core.

Proton-proton chain reaction