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radioactive decay radioactive transmutation radioactive element half-life synthetic element particle accelerator 7.2 Isotopes and Radioactivity
radioactive decay radioactive transmutation radioactive element half-life synthetic element particle accelerator
7.2 Isotopes and Radioactivity
How Many Neutrons • Isotopes with more neutrons are heavier
than isotopes with fewer neutrons.
7.2 Isotopes and Radioactivity
What determines properties? • The number of electrons and how they are
arranged determines chemical properties of an element.
7.2 Isotopes and Radioactivity
What is radioactive decay? • Radioactive decay occurs when an
unstable atomic nucleus changes into another nucleus be emitting one or more particles and energy.
• A nucleus that is unstable and undergoes radioactive decay is called radioactive.
7.2 Isotopes and Radioactivity
Gold-foil Experiment and Radioactive Decay • An alpha particle, which consists of two
protons and two neutrons, was shot at the foil.
• The four particles were blasted out of an isotope as a single particle.
• The isotope gained stability.
7.2 Isotopes and Radioactivity
Gold-foil Experiment and Radioactive Decay (cont.)
• An isotope of americium is shown releasing an alpha particle.
• After losing two protons, americium becomes the element neptunium.
7.2 Isotopes and Radioactivity
Radioactive Decay and Transmutation • Some radioactive isotopes decay by
changing their neutrons into different particles.
• Some trap their own electrons and put them into the nucleus.
• A beta particle is an electron released by the nucleus of an atom.
• When a beta particle is released, it gains a proton and becomes the element with one higher atomic number.
7.2 Isotopes and Radioactivity
Radioactive Decay and Transmutation • One element changing into another is
called transmutation.
(cont.)
7.2 Isotopes and Radioactivity
Uses of Radioactive Decay • Radiation can be used to detect and kill
cancer cells, kill bacteria, fungi, insects, and other things that cause food to spoil.
• Antoine-Henri Bequerel exposed film to radioactive materials.
• Marie Curie separated the radioactive elements in a uranium mineral and discovered polonium and radium.
7.2 Isotopes and Radioactivity
Radioactive Elements and the Periodic Table • Radioactive elements are some of the
heavier elements that have no stable isotopes.
7.2 Isotopes and Radioactivity
Half-life • The half-life of a radioactive element is the
time it takes to decay to half its original mass.
• Some elements have a half life of millions of years, some less than a second.
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7.2 Isotopes and Radioactivity
Synthetic Elements • Synthetic elements are radioactive
elements that are made by scientists or created by nuclear reactions.
• All elements with atomic numbers higher than 92 are synthetic elements and exist only because scientists create them by artificial transmutation.
7.2 Isotopes and Radioactivity
Particle Accelerators • Particle accelerators are giant machines
capable of making particles travel very fast.
• The particles may meld together with target particles to create a new element with a higher atomic number.
7.2 Isotopes and Radioactivity
Element Names • Elements are often named to honor the
scientists who discovered them.
7.2 Isotopes and Radioactivity
Lesson 2 Review
The process by which one element changes into another element is called ____. A radioactive decay B alpha particle decay C transmutation D transformation
7.2 Isotopes and Radioactivity
A B C D
0% 0%0%0%
1. A
2. B
3. C
4. D
Lesson 2 Review
How long would an 80 g sample of barium-131 take to decay to 5 g if the half-life is 12 days? A 12 days B 6 days C 36 days D 48 days
7.2 Isotopes and Radioactivity
A B C D
0% 0%0%0%
1. A
2. B
3. C
4. D
Lesson 2 Review
Elements with atomic numbers higher than 92 are known as ____. A synthetic elements B natural elements C metals D semimetals
7.2 Isotopes and Radioactivity
A B C D
0% 0%0%0%
1. A
2. B
3. C
4. D
End of Lesson 2
7.3 Physical Properties and Changes
physical property melting point boiling point thermal conductivity electrical conductivity physical change
Take out your homework and any late work
What is a physical property?
• A physical property is any characteristic of a material that can be observed without changing the material, such as color, length, or shape.
7.3 Physical Properties and Changes
How is an atom’s structure related to its position on the periodic table?
Melting and Boiling Points • The temperature at which a solid changes
to a liquid is the melting point.
• The temperature at which a liquid changes to a gas is the boiling point.
7.3 Physical Properties and Changes
Attractive Forces • Attractive forces determine the melting and
boiling points of a substance.
– Molecules with weak attraction have low melting and boiling points.
– Molecules with strong attractions have high melting and boiling points.
7.3 Physical Properties and Changes
Pressure • Pressure also affects the boiling point.
• The higher the air pressure, the higher the boiling point.
7.3 Physical Properties and Changes
Density • Density is mass per unit volume of a
substance.
• The volumes are the same, but the density of the gas is less than the solid or liquid because there are fewer gas particles in the container.
7.3 Physical Properties and Changes
Hardness • Hardness is a physical property that shows
how strongly the particles of a substance are held together.
• Diamonds are a form of carbon and are the hardest substance found in nature.
7.3 Physical Properties and Changes
Hardness (cont.)
• This table shows the differences between the structures of diamonds and graphite—both composed of carbon atoms.
7.3 Physical Properties and Changes
Thermal Conductivity • Thermal conductivity is the ability of a
material to transfer heat by collisions of its particles.
• If one part of the metal is heated, the particles move quickly and collide with nearby particles, transferring heat.
• Gases have low thermal conductivity compared to solids because the particles are spread farther apart and do not collide as often.
7.3 Physical Properties and Changes
Gases As Insulators • Gases are sometimes sealed in windows
because they do not conduct heat as easily as glass—less heat is lost through the window.
7.3 Physical Properties and Changes
Electrical Conductivity • Electrical conductivity is the ability of a
material to transfer an electric charge.
7.3 Physical Properties and Changes
What is a physical change? • A physical change is any change in the
size, shape, or state of matter in which the identity of the substance is not changed.
• Dissolving is mixing a substance into another substance to form a solution.
• Mixing is a physical change in which neither substance dissolves into the other.
7.3 Physical Properties and Changes
Changes In State • Changes in state are also physical changes
that are reversible.
– Melting and freezing
– Boiling and condensing
– Sublimation and deposition
7.3 Physical Properties and Changes
