(c) mcgraw hill ryerson 2007. radiation!!! diagnose and treat illnesses kill bacteria and preserve...

(c) McGraw Hill Ryerson 2007


Radiation!!!

• Diagnose and treat illnesses • Kill bacteria and preserve food without chemicals and refrigeration • Process sludge for fertilizer and soil conditioner • Locate underground natural resources and tell a dry hole from a

gusher • Make smoke detectors, nonstick frypans, and ice cream • Grow stronger crops • Power satellites and provide future electrical needs for space

laboratories with people on board • Design instruments, techniques, and equipment; measure air

pollution • Prove the age of works of art and assist in determining their

authenticity


7.1 Atomic Theory and Radioactive Decay

• Natural background radiation exists all around us. This radiation consists of high energy particles or waves being emitted from a

variety of materials.

See pages 286 - 287The electromagnetic spectrum


7.1 Atomic Theory and Radioactive Decay

• Radioactivity is the release of high-energy particles or waves. Can be beneficial

X rays, radiation therapy, and electricity generation

Can be harmful. High-energy particles and waves damage DNA in our cells.

Can be interesting When atoms lose high-energy particles and waves, ions or even new atoms

can be formed.

See pages 286 - 287


Searching for Invisible Rays

Roentgen named X rays with an “X” 100 years ago because they were previously unknown.

Becquerel realized uranium emitted seemingly invisible energy as well. Marie Curie and her husband Pierre named this energy radioactivity.

Early discoveries of radiation relied on photographic equipment. Later, more sophisticated devices such as the Geiger-Müller counter were

developed to more precisely measure radioactivity.

See pages 288 - 289

Radium salts, after being placed on a photographic

plate, leave behind the dark traces of radiation.


Wihelm Roentgen

• Received the 1st Nobel prize in physics (1901) for discovering the X Ray

• He was expelled for refusing to reveal the identity of a classmate guilty of drawing an unflattering portrait of one of the school's teachers

• Röntgen refused to take out patents related to his discovery, as he wanted mankind as a whole to benefit from practical applications of the same (personal statement). He did not even want the rays to be named after him


Henri Becquerel

• Shared his Nobel prize with Marie and Pierre Curie (physics 1903)

• Accidentally discovered radioactivity

• The SI unit for radioactivity, the becquerel (Bq), is named after him

• 2 craters are named after him 1 on the moon, 1 on mars


Marie Curie

• 1st person honoured with 2 Nobel prizes

• 1st woman honoured with a Nobel prize

• Only person to win 2 Nobel prizes in 2 sciences

• Husband awarded Nobel prize in physics at the same time

• Daughter and son-in-law also received Nobel prizes

• Discovered polonium and radium• Died from aplastic anemia

Even her cookbook is radioactive


Isotopes and Mass Number

• Isotopes are different atoms of the same element same number of protons and therefore the same atomic number as each other. different numbers of neutrons, therefore isotopes have different mass

numbers.(Mass number refers to the protons plus neutrons in an isotope)(Atomic mass = proportional average of the mass numbers for all isotopes of

an element.)• 19.9% of boron atoms have 5 neutrons, 80.1% have 6 neutrons• 19.9% have a mass number of 10, and 80.1% have a mass number of 11• (.199 * 10) + (.801*11) = 10.8 = atomic mass of boron

See page 289 - 290


Isotopes and Mass Number

• Same element = same # of protons = same atomic #• Isotope = same element, different # of neutrons• Different # of neutrons = different mass #

Mass # = # of protons + # of neutrons Atomic mass = proportional avg. of the mass #’s for all isotopes

of an element


Standard atomic notation

• Eg:

• All isotopes of potassium are represented by the symbol, K• All isotopes of potassium have 19 protons• The difference is their neutrons (eg: 39, 40, 41)

1939 K, 19

40 K, 1941K


Whiteboard Check

• P. 291 #2

• A laboratory analyzes the composition of the two naturally occuring isotopes of bromine. One of the isotopes has an atomic numbers of 35 and a mass number of 81. State the following for the isotope:

a) # of protons b) # of neutrons

c) name of the isotope d) standard atomic notation


Whiteboard Check Answers

• A) 35• B) 46• C) bromine – 81• D) 81/35 bromine


Whiteboard Check

• What is the atomic mass of potassium, knowing that the ratios in nature of potassium isotopes are:

• 93.2% is potassium-39• 1.0% is potassium-40• 6.7% is potassium-41


Whiteboard Answer

• Atomic mass is the proportional average of all naturally occuring isotopes

• 93.2% is potassium-39• 1.0% is potassium-40• 6.7% is potassium-41

• Atomic mass = (0.932 x 39) + (0.001 x 40) + (0.067 x 41) = 39.1


Representing Isotopes

Potassium is found in nature in a certain ratio of isotopes. 93.2% is potassium-39, 1.0% is potassium-40, and 6.7% is potassium-41 Atomic mass = (0.932 x 39) + (0.001 x 40) + (0.067 x 41) = 39.1

See page 290


Representing Isotopes

• Isotopes are written using standard atomic notation. Chemical symbol + atomic number + mass number. Potassium has three isotopes,

See page 290

1939 K, 19

40 K, 1941K


Radioactive Decay

• Unlike all previously discovered chemical reactions, radioactivity sometimes results in the formation of completely new atoms. Radioactivity results from having an unstable nucleus.

Radioactive decay • Occurs when these nuclei lose energy and break apart• Releases energy from the nucleus as radiation.

An element may have only certain isotopes that are radioactive.• These are called radioisotopes

release energy until they become stable, often as different atoms.

See page 293


Radioactive Decay

See page 293Radioisotope uranium-238 decays in several stages until it finally becomes lead-206.


Radioactive Decay

• Radioactivity results from having an unstable nucleus• When these nuclei lose energy and break apart, decay occurs

releases energy from the nucleus as radiation

• Radioisotopes = isotopes that are radioactive Not all isotopes are radioactive


Three Types of Radiation

• Rutherford identified three types of radiation using an electric field. Positive alpha particles were attracted to the negative plate. Negative beta particles were attracted to the positive plate. Neutral gamma rays did not move towards any plate.

See page 294


Three Types of Radiation (continued) :Alpha Radiation

• Alpha radiation is a stream of alpha particles. Alpha particles are slow and penetrate materials much less than the other

forms of radiation. A sheet of paper will stop an alpha particle.

See page 294 - 295

Radium-226 releases an alpha particle and becomes Radon-222. Radon has two less protons than radium.


Three Types of Radiation (continued) :Alpha Radiation

• Alpha decay releases alpha particles. positively charged most massive of the radiation types. essentially the same as helium atoms. represented by the symbols .

two protons Has a charge of 2+.

See page 294 - 295

24 or 2

4 He


Alpha particles

• Most massive of the radioactive particles can be stopped by a sheet of paper

• Releases 2 neutrons & 2 protons• Has +2 charge

24 or 2

4 He


Whiteboard Check

• P 295 # 1

• Try the following alpha decay problems yourself. You can refer to the periodic table in Figure 4.3 on page 172 (or use your data booklet!)

• A) 208/84 Po ________ + 4/2 alpha particle• B) 231/91 Pa ________ + 4/2 He• C) ________ 221/87 Fr + 4/2 alpha particle• D) ________ 192/77 Ir + 4/2 alpha particle• E) ________ 207/85 At + 4/2 He


Whiteboard Answers

• A) 204/82 Pb• B) 227/89 Ac• C) 225/89 Ac• D) 196/79 Au• E) 211/87 Fr


Three Types of Radiation (continued) :Beta Radiation

• A beta particle is an electron and is negatively charged. It takes a thin sheet of aluminum foil to stop a beta particle.

See page 296

Iodine-131 releases a beta particle and becomes xenon-131. A neutron has turned into a proton and the released electron.

53131I 54

131 Xe + –10

or

53131I 54

131 Xe + –10e


Three Types of Radiation (continued) :Beta Radiation

• Beta decay occurs when a neutron changes into a proton + beta particle (an electron).

• The proton stays in the nucleus, and the electron is released.

is negatively charged. represented by the symbols . assigned a mass of 0.

See page 296

-10 or -1

0e


Beta particles

• Beta particle = an electron

• 0 neutrons, 0 protons, -1 charge• Beta decay occurs when a neutron changes into a proton + an electron.

The proton stays in the nucleus, and the electron is release

• The original element GAINS A PROTON AND LOSES A NEUTRON

Can be stopped by sheet of aluminum metal

-10 or -1

0e

53131I 54

131 Xe + –10

or

53131I 54

131 Xe + –10e


Whiteboard Check

• P 296 # 1

• Try the following beta decay problems yourself:

• A) 14/6 C _________ + 0/-1 beta particle• B) 6/2 He _________ + 0/-1 beta particle• C) 24/11 Na ________ + 0/-1 beta particle• D) ________ 201/80 Hg + 0/-1 beta particle• E) ________ 52/27 Co + 0/-1 beta particle• F) ________ 42/20 Ca + 0/-1 beta particle


Whiteboard Answers

• A) 14/7 N• B) 6/3 Li• C) 24/12 Mg• D) 201/79 Au• E) 52/26 Fe• F) 42/19 K


Three Types of Radiation (continued) :Gamma Radiation

• Gamma radiation is a ray of high-energy, short-wavelength radiation. no charge no mass, represented by the symbol highest-energy form of electromagnetic radiation.

It takes thick blocks of lead or concrete to stop gamma rays.

See page 297

00


Three Types of Radiation (continued) :Gamma Radiation

Gamma decay results from energy being released from a high-energy nucleus.

Often, other kinds of radioactive decay will also release gamma radiation. Uranium-238 decays into an alpha particle and also releases gamma rays.

See page 297

2860 Ni* 28

60 Ni + 00

92238 U 90

234 Th + 24 He + 2


Gamma Radiation

• high-energy, short-wavelength radiation• Highest energy of EM wave• no charge and no mass

• Takes thick blocks of lead or concrete to stop gamma rays

• No change in the element, just high energy released

00

2860 Ni* 28

60 Ni + 00


Radiation and Radioactive Decay Summaries, and Nuclear Equations for Radioactive Decay

• Nuclear equations are written like chemical equations, but represent changes in the nucleus of atoms. Chemical equations represent changes in the position of atoms, not

changes to the atoms themselves.

1. The sum of the mass numbers does not change.2. The sum of the charges in the nucleus does not change.

See pages 298 - 299

Take the Section 7.1 Quiz


Radiation and Radioactive Decay Summaries, and Nuclear Equations for Radioactive Decay

See pages 298 - 299

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