7.2 Isotopes and Radioactivity. radioactive decay radioactive transmutation radioactive element half-life synthetic element particle accelerator

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1 7.2 Isotopes and Radioactivity radioactive decay radioactive transmutation radioactive element half-life synthetic element particle accelerator

2 How Many Neutrons 7.2 Isotopes and Radioactivity Isotopes with more neutrons are heavier than isotopes with fewer neutrons.

3 What determines properties? 7.2 Isotopes and Radioactivity The number of electrons and how they are arranged determines chemical properties of an element.

4 What is radioactive decay? 7.2 Isotopes and Radioactivity 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.

5 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

6 Gold-foil Experiment and Radioactive Decay (cont.) 7.2 Isotopes and Radioactivity An isotope of americium is shown releasing an alpha particle. After losing two protons, americium becomes the element neptunium.

7 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.

8 7.2 Isotopes and Radioactivity Radioactive Decay and Transmutation One element changing into another is called transmutation. (cont.)

9 Uses of Radioactive Decay 7.2 Isotopes and Radioactivity 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.

10 Radioactive Elements and the Periodic Table 7.2 Isotopes and Radioactivity Radioactive elements are some of the heavier elements that have no stable isotopes.

11 Half-life 7.2 Isotopes and Radioactivity 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. The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again.

12 Synthetic Elements 7.2 Isotopes and Radioactivity 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.

13 Particle Accelerators 7.2 Isotopes and Radioactivity 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.

14 Element Names 7.2 Isotopes and Radioactivity Elements are often named to honor the scientists who discovered them.

15 7.2 Isotopes and Radioactivity A B C D The process by which one element changes into another element is called. A radioactive decay B alpha particle decay C transmutation D transformation 0% 0% 0% 0% A B C D

16 7.2 Isotopes and Radioactivity A B C D 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 0% 0% 0% 0% A B C D

17 7.2 Isotopes and Radioactivity A B C D Elements with atomic numbers higher than 92 are known as. A synthetic elements B natural elements C metals D semimetals 0% 0% 0% 0% A B C D

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19 7.3 Physical Properties and Changes physical property melting point boiling point thermal conductivity electrical conductivity physical change

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21 What is a physical property? 7.3 Physical Properties and Changes A physical property is any characteristic of a material that can be observed without changing the material, such as color, length, or shape. How is an atom s structure related to its position on the periodic table?

22 Melting and Boiling Points 7.3 Physical Properties and Changes 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.

23 Attractive Forces 7.3 Physical Properties and Changes 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.

24 Pressure Pressure also affects the boiling point. The higher the air pressure, the higher the boiling point. 7.3 Physical Properties and Changes

25 Density 7.3 Physical Properties and Changes 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.

26 Hardness 7.3 Physical Properties and Changes 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.

27 Hardness (cont.) 7.3 Physical Properties and Changes This table shows the differences between the structures of diamonds and graphite both composed of carbon atoms.

28 Thermal Conductivity 7.3 Physical Properties and Changes 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.

29 Gases As Insulators 7.3 Physical Properties and Changes Gases are sometimes sealed in windows because they do not conduct heat as easily as glass less heat is lost through the window.

30 Electrical Conductivity 7.3 Physical Properties and Changes Electrical conductivity is the ability of a material to transfer an electric charge.

31 What is a physical change? 7.3 Physical Properties and Changes 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.

32 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