chapter 18 nuclear reactions. chemical reactions occur in the outer electron energy level valance...

Chapter 18Nuclear Reactions

Chemical Reactions

Occur in the outer electron energy levelValance electrons Ionic or covalent bonding occurs

Nuclear Reactions

Occur in the nucleus of the atom

Involve the NUCLEONS

Nucleons = protons & neutrons

Transmutation occurs

Strong Nuclear Force

Protons are positively charged and repel each other

←+ +→Strong Nuclear Force = the force that

causes the protons and neutrons in the nucleus to stick together and holds the nucleus tightly together.

ISOTOPES

Atoms of the same element with a different number of neutrons.

Ex: carbon-12 & carbon-14 Carbon-12

6 protons 6 neutrons 6 electrons

Carbon-14 6 protons 8 neutrons 6 electrons

3 Types of RadioactivityRadioactive Decay

ALPHA PARTICLE (α)

BETA PARTICLE (β)

GAMMA RAYS (γ)

ALPHA PARTICLE2 protons & 2 neutronsnucleus of a helium atomweakest type of radiation12 inches max. distance travel

What happens to the numbers of particles in the nucleus after alpha decay?

BETA PARTICLE

an electron emitted from the nucleusA neutron splits into a proton & electronThe electron is expelled out of the nucleus The proton stays and increases the number of protons

by one. The atomic number of the element increases by one The element changes into the next higher element on

the periodic table. 100x stronger than an alpha particle

What happens to the numbers of particles in the nucleus after beta decay?

Gamma Rays

An electromagnetic wave - packet of energyA The energy readjustment in the nucleusMost powerful form of radiationThe sun is a great source of gamma radiationDANGEROUS to living organisms

Stopped by:

alpha – paper/skin

beta – wood

gamma – several feet

of concrete/lead

Gamma Ray Photography From Space

Antoine Henri Becquerel

In 1896, radioactivity was first discovered.

Used uranium salts = placed them near a photographic film plate.

exposed the film (below)

Awarded Nobel Prize in 1903 in Physics

Pierre & Marie Curie (1898)

Discover the radioactive properties of radium & polonium Together awarded the Nobel Prize in 1903 (physics) along

with Henri Becquerel Marie is award a second Nobel Prize in 1911 (chemistry) Pierre is killed in an accident in 1906, Marie continues

working with radioactive substances.

Transmutation= changes from one element to another

element during α and β decay.

Alpha Decay = mass number decreases by 4 atomic number decreases by 2

Beta Decay = mass number does not change atomic number increases by 1

Alpha Decay

Uranium-238 has 92 protons

After alpha decay (2 protons & 2 neutrons leave the nucleus)

Becomes Thorium-234 and has 90 protons

Beta Decay

Carbon-14 has 6 protons & 8 neutrons

After beta decay (a neutron is split into a proton and electron

& the electron is expelled from the nucleus)

Becomes Nitrogen-14 and has 7 protons and 7 neutrons

Half Life

= the time it takes for one half of the mass of a radioactive substance to decay.Ex: carbon-14 = 5730 years

100 gram sample – In 5730 yrs = 50 grams C-14 & 50 grams N-14– In11,460 yrs = 25 grams C-14 & 75 grams N-14– In 17,190 yrs = 12.5 grams C-14 & 87.5 grams N-14

Nuclear Reactions

Nuclear Fission

Nuclear Fusion

Nuclear Fission

= the splitting of the nucleus into two smaller nuclei

Neutrons are used to split the nucleusAdditional neutrons are released to continue on

to hit/split other nuclei

Chain Reactions

Critical Mass (required) = concentration of radioactive atoms in a sample.Controlled Chain Reaction = many of the neutrons

that are produced are absorbed in “control rods” prevent excess energy to be released.

Ex. Nuclear Power Plants

Uncontrolled Chain Reaction = all the neutrons are allowed to continue to hit/split other nuclei causing massive amounts of energy to be released all at once.Ex. Atomic Bomb (used on Japan in 1945)

Controlled Chain Reaction

Uncontrolled Chain Reaction

Nuclear Fusion

= the joining of two smaller nuclei into a single larger nucleus

Extremely more powerful release of energy than fission

Requires a temperature of 10 million degrees Celsius

Also known as a thermonuclear reactionex: H-bomb and the sun/stars

Fusion Explosions

History of Chain

Reactions The concept was first developed by Leó Szilárd in

1933 which he then proceeded to get a patent on the concept the following year.

Leo Szilárd attempted to create a chain reaction using beryllium and indium in 1936 but was unsuccessful.

The first artificial self-sustaining nuclear chain reaction was initiated by the Metallurgical Laboratory, led by Enrico Fermi and Leó Szilárd, in a racquets court below the bleachers of Stagg Field at the University of Chicago on December 2, 1942 during the Manhattan Project. (see link above to Einstein’s letter in 1939)

The Manhattan Project

September 1935: Nuremburg Laws begin severe persecution of Jews

March 1936: Occupation of the German Rhineland

July 1937: Japan invades China November 1937: The Axis Alliance is created

by a pact between Germany, Japan, and Italy March 1938: the Anschluss (occupation of

Austria by Germany) September 1938: German occupation of the

Sudetenland in Czechoslovakia

World War Breaks out in Europe in 1939

Szilard drafted a letter in consultation with Albert Einstein that was addressed from Einstein to President F.D. Roosevelt and which warned him of the possibility of nuclear weapons (the "Einstein Letter").

This letter was delivered to FDR on October 11, 1939, and ten days later the first meeting of the Advisory Committee on Uranium (the "Briggs Uranium Committee") was held in Washington, DC on Pres. Roosevelt's order.

December 7, 1941

USA Goes to Warofficial founding in August, the

Manhattan Project really began on September 17, 1942

Col. Leslie Richard Groves heads the project from the government’s end

Groves asks Dr. J. Robert Oppenheimer to head the project from the scientists end.

“The Gadget”

Code Name = Trinity

July 16, 1945 - At 5:29:45 a.m. “The Gadget” was detonated in the first atomic explosion in history. The explosive yield was 20-22 Kt, vaporizing the steel tower.

TARGETS???

May 8, 1945 V-E Day Germany surrendersJapan now becomes the targetSome scientists object to targeting Japan; the

Nazis caused many of them to have to leave their homes and lost family members to the Holocaust.

August 6, 1945

“Little Boy” is used on Hiroshima, Japan

Dropped from the B-29 bomber named “The Enola Gay”

5 mile circle of destructionest. 78,000 killed & 70,000

injured

August 9, 1945

“Fat Man” is used on Nagasaki, Japan

2 mile circle of destruction

40,000 killed & 25,000 injured

Japan unconditionally surrenders a few days later & WWII is officially over

VJ Day (Victory over Japan) August 15, 1945

Further Nuclear Developments

August 1949 = Soviet Union tests their first atomic bomb after Russian spies delivered US secret bomb blue-prints

November 1952 = United States the first Hydrogen bomb (H-bomb) 10 MT in strength, USSR tests their first H-bomb in Aug. 1953

Other Atomic weapons countries include Great Britain, China, France, India, Pakistan, and possibly Israel.

North Korea & Iran are currently in the news for seeking nuclear capabilities.

What is the problem with these counties having nuclear weapons?

• North Korea = violation of the treaty to end the Korean War.

• Iran = violation of a United Nations Resolution

BOTH WOULD/COULD BE CONSIDERED ACTS OF WAR!!!