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Chapter 18 Nuclear Reactions. Chemical Reactions  Occur in the outer electron energy level  Valance electrons.

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Presentation on theme: "Chapter 18 Nuclear Reactions. Chemical Reactions  Occur in the outer electron energy level  Valance electrons."— Presentation transcript:

1 Chapter 18 Nuclear Reactions

2 Chemical Reactions  Occur in the outer electron energy level  Valance electrons

3 Nuclear Reactions  Occur in the nucleus of the atom  Involve the NUCLEONS  Nucleons = protons & neutrons

4 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.

5 Radioactivity When the strong force of an atom is not strong enough to hold the nucleus together, then the atom tends to decay The atoms are considered unstable, or radioactive The process of decay is called radioactivity and in the process particles and energy are released and the atom is changed into another type of atom

6 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 Carbon 12 is a stable isotope of carbon. Carbon- 14 is unstable or radioactive because the addition of the two neutrons have disrupted the strong force and made the nucleus start to decay, or break apart.

7 3 Types of Radioactivity Radioactive Decay  ALPHA PARTICLE ( α )  BETA PARTICLE ( β )  GAMMA RAYS ( γ )

8 ALPHA PARTICLE  2 protons & 2 neutrons  nucleus of a helium atom  weakest type of radiation  can be stopped by a piece of paper  12 inches max. distance travel

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

10 BETA PARTICLE  an electron emitted from around the nucleus  A neutron splits into a proton & electron  The 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

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

12 Gamma Rays  An electromagnetic wave  A packet of energy  The energy readjustment in the nucleus  Most powerful form of radiation  The sun is a great source of gamma radiation

13 Gamma Radiation, Cont Gamma rays are very harmful to cells. They can damage the DNA of your cells and mutate them, which can cause cancer High amounts of gamma ray exposure can cause death Low amounts are normal and you are exposed to them all the time Cannot be easily blocked. Inches of concrete lined with lead can stop a gamma ray

14 Gamma Ray Photography From Space

15 REMEMBER! Gamma rays are light!

16 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

17 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. She eventually dies of cancer

18 Transmutation  = changes from one element to another element during α and β decay.  Alpha Decay = mass number decreases by 4 and the atomic number decreases by 2  Beta Decay = mass number does not change and the atomic number increases by 1

19 Alpha Decay  Uranium-238 has 92 protons  After alpha decay (2 protons & 2 neutrons leave the nucleus)  Becomes Thorium-234 and has 90 protons

20 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

21 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

22 Radioactive Dating Half life is used by scientists to find out how old a fossil or a rock is Carbon 14 is often used to date fossils What type of isotope used depends on the material being dated Uranium is often used to date rocks because many rocks contain uranium already

23 Detecting Radioactivity Cloud chambers track alpha and beta particles Chamber is filled with a cloud of vapor Alpha particles leave short thick trails Beta particles leave long thin trails

24 Bubble Chamber Holds a super heated liquid that doesn’t boil due to high pressure When a radioactive particle passes through the liquid, trails of bubbles form

25 Geiger Counter Pops or clicks in the presence of radiation Uses electricity and current to cause a flow of electrons The current is amplified to produce a clicking sound

26 Background Radiation You are exposed to radiation every day Sources of background radiation vary and amounts are usually not harmful

27 Nuclear Reactions  Nuclear Fission  Nuclear Fusion

28 Nuclear Fission Nuclear Fission  the splitting of the nucleus into two smaller nuclei  Neutrons are used to split the nucleus  Additional neutrons are released to continue on to hit/split other nuclei

29 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)

30 Controlled Chain Reaction

31 Generating Electricity Nuclear power is only one way to generate electricity It is often cheaper and easier than other forms of energy (ie using wind or coal or water) However, there are safety concerns that you must take into consideration

32 Nuclear Reactors Used to generate electricity Used to power ships, submarines Risk of meltdown, must be kept cool to prevent uncontrolled chain reactions

33 Nuclear Reactor

34 Three Mile Island Accident March 28, 1979– Harrisburg PA– Three Mile Island Nuclear Power Plant: A partial meltdown occurred in one reactor due to a stuck valve. Negligible amounts of radiation were released into the environment

35 Chernobyl - April 26,1986 Power Plant in the Ukraine Explosion and fire that was caused by a power surge Explosion and fire that was caused by a power surge 31 people died of acute radiation sickness You still can’t live in that area today Crops were affected, many cases of cancer recorded, especially in children

36 Chernobyl Pripyat, Ukraine

37 Fukushima - March 11, 2011 Ongoing nuclear accident in Japan at the Fukushima power plant Caused partial or full meltdown to reactor, thanks to earthquake and Tsunami Power failure to coolant main cause Effects of the disaster are ongoing and unknown at this time

38 Uncontrolled Chain Reaction

39 Nuclear Fusion Nuclear Fusion  = the joining of two smaller nuclei into a single larger nucleus  Powers the sun, very hard to duplicate on Earth because of the high pressure and temperature needed  Extremely more powerful release of energy than fission  Also known as a thermonuclear reaction  ex: H-bomb and the sun/stars

40 Fusion Explosions

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