Chapter 4 Section 4

Natural and Synthetic Elements 93 naturally occurring elements 93 naturally occurring elements Are they all found on Earth? Are they all found on Earth? –No, technetium, promethium, and neptunium are detected in the spectra of stars How do we get the rest of our elements? How do we get the rest of our elements? –They are synthetic or created in a lab

Naturally Occurring Elements The Big Bang Theory The Big Bang Theory –The universe “exploded” –After this the temperatures were in the millions of Kelvins –Only energy could exist not matter –As it expanded it cooled –When it cooled the energy was converted to matter in the form of electrons, protons, and neutrons

Naturally Occurring Elements Big Bang Theory Big Bang Theory –As the universe continued to cool the first atoms formed – mostly hydrogen –Over time gravitational attraction pulled the clumps of hydrogen together –The clouds became denser, pressure increased, and temperature increased. This created stars

Naturally Occurring Elements What takes place in the center of stars? What takes place in the center of stars? –Nuclear reactions Nuclear reaction: Nuclear reaction: –Reaction that involves a change in the composition of the nucleus of an atom –Ex: Hydrogen nuclei fused with one another to form helium nuclei

Naturally Occurring Elements Nuclear Fusion: Nuclear Fusion: –Takes place under extreme heat –Kinetic energy of the nuclei is great enough to overcome the repulsion between the protons Figure 4-31 Figure 4-31 –The mass lost is converted into energy

Naturally Occurring Elements Hydrogen is being used = star shrinking and temperature increasing Hydrogen is being used = star shrinking and temperature increasing As temp increases the helium fuse with another to form elements of higher atomic numbers As temp increases the helium fuse with another to form elements of higher atomic numbers As the temp increases more elements of even higher atomic #’s are created As the temp increases more elements of even higher atomic #’s are created Figure 4-32 Figure 4-32

Naturally Occurring Elements What are the most massive atoms that can be created this way? What are the most massive atoms that can be created this way? –Iron and Nickel When all of the hydrogen and helium are used up the star collapses and then expands as a red giant When all of the hydrogen and helium are used up the star collapses and then expands as a red giant

Naturally Occurring Elements When the red giant forms free protons and neutrons are produced When the red giant forms free protons and neutrons are produced –They are absorbed by the nuclei of other atoms creating elements with higher atomic numbers –The red giant expels some of its matter into space as well as the elements it produced

Naturally Occurring Elements If the star is larger than the sun it eventually explodes into a supernova If the star is larger than the sun it eventually explodes into a supernova All of the elements are spread across space All of the elements are spread across space Some of the exploded matter is eventually condensed into a new star Some of the exploded matter is eventually condensed into a new star

Naturally Occurring Elements The new stars are mostly hydrogen but will still contain the heavier elements too The new stars are mostly hydrogen but will still contain the heavier elements too This creates a third generation star This creates a third generation star The sun is a fourth or fifth generation star The sun is a fourth or fifth generation star When the sun first formed it contained all the naturally occurring elements When the sun first formed it contained all the naturally occurring elements

Artificial Elements Transmutation: Transmutation: –Changing 1 nucleus into another by radioactive disintegration or bombardment with other particles –High-speed alpha particles passing through water vapor in a cloud chamber  Noted long thin tracks which were caused by protons  Same tracks were found when alpha particles passed through air

Artificial Elements This process helped scientists discover that atomic nuclei in the air were disintegrating when struck by helium nuclei into hydrogen nuclei plus the nuclei of another atom This process helped scientists discover that atomic nuclei in the air were disintegrating when struck by helium nuclei into hydrogen nuclei plus the nuclei of another atom They found that transmutations occurred by bombarding various elements with alpha particles They found that transmutations occurred by bombarding various elements with alpha particles

Cyclotron Invented in 1930 Invented in 1930 Charged particles are given successive pulses of energy Charged particles are given successive pulses of energy They are accelerated to very high energies They are accelerated to very high energies The energetic ions are then made to collide with atomic nuclei The energetic ions are then made to collide with atomic nuclei The accelerated ions fuse with the target nuclei to produce a higher atomic number The accelerated ions fuse with the target nuclei to produce a higher atomic number

Problems There is a limit to the energies attained by a cyclotron There is a limit to the energies attained by a cyclotron The problem was that the particle’s energy had to be balanced by an increase in mass The problem was that the particle’s energy had to be balanced by an increase in mass Due to the increased mass the particle’s accelerated more slowly causing it to arrive to late Due to the increased mass the particle’s accelerated more slowly causing it to arrive to late

Synchrotron A synchrotron times the impulses to match the particle acceleration A synchrotron times the impulses to match the particle acceleration Downfall: Downfall: –Can accelerate fewer types of particles than a cyclotron Bonus: Bonus: –Enormous energies can be attained

Synchrotron Once they are accelerated they collide head on with each other Once they are accelerated they collide head on with each other Figure 4-34 Figure 4-34 Superheavy elements can be created Superheavy elements can be created

Today Scientists are trying to create superheavy elements that are more stable than those prepared so far Scientists are trying to create superheavy elements that are more stable than those prepared so far They think there is an “island of stability” in the region of atomic number 114 They think there is an “island of stability” in the region of atomic number 114 Right now they exist for only a short amount of time and identification is very difficult Right now they exist for only a short amount of time and identification is very difficult