Chapter 7 - Chapter 7 - RadioactivityRadioactivity

Science 10Science 10

7.1 7.1 Atomic Theory and Atomic Theory and Radioactive DecayRadioactive Decay

Natural Natural background radiationbackground radiation exists all around exists all around us.us.

Radioactivity Radioactivity is the release of high energy is the release of high energy particles or waves.particles or waves.– We use radioactive materials for many things:We use radioactive materials for many things:

X-rays, radiation therapy and electricity generation are X-rays, radiation therapy and electricity generation are beneficial.beneficial.

High energy particles and waves can do damage to DNA in High energy particles and waves can do damage to DNA in our cells.our cells.

– When atoms lose high energy particles and waves, When atoms lose high energy particles and waves, ions or even new atoms can be formed.ions or even new atoms can be formed.

– High energy waves and particles are called High energy waves and particles are called radiationradiation when they leave the atom.when they leave the atom.

The Electromagnetic Spectrum

Some History:Some History: Radiation is everywhere, but can be Radiation is everywhere, but can be

difficult to detect.difficult to detect.– Roentgen named X-rays with an “X” Roentgen named X-rays with an “X”

100 years ago because they were 100 years ago because they were previously unknown.previously unknown.

– Becquerel realized uranium emitted Becquerel realized uranium emitted seemingly invisible energy.seemingly invisible energy.

– Marie Curie and her husband Pierre named Marie Curie and her husband Pierre named the energy radioactivity.the energy radioactivity. Early discoveries of radiation relied on Early discoveries of radiation relied on

photographic equipmentphotographic equipment

– Later, more sophisticated devices such as the Later, more sophisticated devices such as the Geiger-Müller counter were developed to Geiger-Müller counter were developed to more precisely measure radioactivity.more precisely measure radioactivity.

Radium salts, after being placed on a

photographic plate, leave behind the dark

traces of radiation.

IsotopesIsotopes

are different atoms of the same are different atoms of the same element, with a different number of element, with a different number of neutrons in the nucleus.neutrons in the nucleus.– Changing the # of neutrons changes the Changing the # of neutrons changes the

mass numbermass number Remember: mass # = # protons + # neutronsRemember: mass # = # protons + # neutrons

– isotopes still have the same:isotopes still have the same: number of protons / atomic numbernumber of protons / atomic number element symbolelement symbol

Atomic Mass (the decimal Atomic Mass (the decimal #’s)#’s)

Atomic mass = average of the mass Atomic mass = average of the mass numbers for all isotopes of an numbers for all isotopes of an element.element.– If 19.9% of boron atoms have 5 If 19.9% of boron atoms have 5

neutrons, 80.1% have 6 neutronsneutrons, 80.1% have 6 neutrons– 19.9% have a mass number of 10, and 19.9% have a mass number of 10, and

80.1% have a mass number of 1180.1% have a mass number of 11– (.199 * 10) + (.801*11) = 10.8 (.199 * 10) + (.801*11) = 10.8 – atomic mass of boron = 10.8atomic mass of boron = 10.8

Representing IsotopesRepresenting Isotopes

Isotopes are written using standard Isotopes are written using standard atomic notation.atomic notation.– Chemical symbol + atomic number + mass Chemical symbol + atomic number + mass

number.number.– Potassium has three isotopes, Potassium has three isotopes,

39 40 4119 19 19K, K, K

Potassium is found in nature in a Potassium is found in nature in a certain ratio of isotopescertain ratio of isotopes

93.2% is potassium-3993.2% is potassium-39 1.0% is potassium-401.0% is potassium-40 6.7% is potassium-41 6.7% is potassium-41

– Atomic mass Atomic mass

= (.932 x 39) + (.001 x 40) + (.067 x = (.932 x 39) + (.001 x 40) + (.067 x 41) 41)

= 39.1= 39.1