Directions for teachers:
The article “Strontium found in neutron star crash” describes scientists’ discovery that the element strontium was created during a neutron star collision. Have your students read this recent news story to encourage them to think about how elements are made. Remind students that elements are not only the building blocks of all life-forms on Earth, but are also the building blocks of planets and stars. Then work through the prompts using the instructions below.
1. Use the first four prompts to review and discuss concepts related to how elements are made, such as atomic structure, stability, nuclear fusion and stellar evolution, with your students.
Background information covering principles of atomic stability, fusion reactions and the life cycle of stars can be found in Star light, star bright in our Digital Library. Atoms, ions and isotopes, oh why? covers concepts related to atomic structure and stability.
2. Allow students to choose to read one of two additional articles — “We are stardust” (Readability: 7.1), about nucleosynthesis, or “Extreme elements push the boundaries of the periodic table” (Readability: 10.7), about creating superheavy elements in the lab. After reading, students should form into small groups based on their article choice and use the related prompts to discuss the ways that elements are created.
3. After students discuss the articles in small groups, bring the class back together to discuss the closing prompts, which allow groups to share what they learned, think about what types of scientists are interested in element formation and about how energy plays a role in element formation.
The directions for students follows:
Getting warmed up
Review the following questions as a class.
1. What subatomic particles exist in an atom? Where are these particles generally located, and what forces hold them together?
2. Why are some atoms unstable? What are two ways that the numbers of particles in an atom could make it unstable? What happens when an atom is not stable? How are ions produced, and what is nuclear decay?
3. How do we define an atom of a particular element? How do we distinguish between one element and another, and why is doing so useful? What techniques allow us to identify the presence of different elements?
4. What is nuclear fusion? How does a star form, live and die? How does nuclear fusion relate to a star’s life cycle? How does a star’s mass affect its life cycle, and how does our sun’s size compare with that of other stars?
The star producer
If you have selected “We are stardust,” read the article through the section “Death of a star” and discuss the following prompts in your group.
1. What types of stellar events can produce new elements?
Elements can form in a star throughout its life. They can also form when two stars collide and when a star explodes as it dies.
2. What elements were created in the Big Bang? Describe the relative amounts of the elements in the very early universe’s giant gas clouds.
Hydrogen and helium were created in the Big Bang. About 90 percent of the universe’s giant gas clouds were hydrogen atoms and the rest were helium.
3. What elements are created in a living star, and how are they created? What types of elements cannot be born from living stars?
Living stars can create elements as heavy or lighter than iron. The intense heat of the sun can cause atoms to collide and fuse, creating heavier elements from lighter ones. Elements heavier than iron cannot be produced in living stars because the stars are not big or hot enough.
4. How does a star’s size and temperature affect the elements it can create while living? What types of elements are created by our sun?
The bigger and hotter the star, the heavier the elements it can create. The sun is considered an average-size star, which means it creates lighter elements, mainly helium but also some other elements including nitrogen.
5. How do relatively small stars die? How do relatively big stars die? Which process can produce more massive elements? Explain.
When a small star dies, its core collapses and the rest of it expands into a huge ball, cooling as it grows. This dying star becomes a red giant, and many of its atoms will be lost in space. When a bigger star dies, its core also collapses, becoming hot and dense and forging elements. It then expands and collapses again, which in turn creates even heavier elements. This process continues until it self-destructs in a giant explosion called a supernova that creates elements heavier than iron. A bigger star’s death creates heavier elements because the star has more energy.
Artificial assembly time
If you have selected “Extreme elements push the boundaries of the periodic table,” read the article through the section “Relativity rules” and discuss the following prompts in your group.
1. What types of elements must be created by scientists artificially?
Elements heavier than uranium (element 92) do not exist in significant quantities in nature and must be created through artificial means.
2. What techniques are used by scientists to create these elements?
To create superheavy elements, scientists bombard an existing element with neutrons or small atomic nuclei using a particle accelerator or slam beams of heavy atoms onto a target containing another element. In either case, the bits being smashed must fuse together to create a new atom with a bigger nucleus.
3. Where do scientists create superheavy elements? What equipment is needed?
There aren’t many locations in the world where scientists can create these new elements because of the highly specialized equipment, notably high-energy accelerators, needed. There are a few labs where the work is done, including in Russia and Japan.
4. How long do the heaviest labmade elements exist? What does their lifetime tell you about their stability? What happens to them when they no longer exist? What elements are left over and how are they relate to the original element?
Superheavy elements start to decay instants after they’re formed. Their nuclei are so big that they are generally unstable and start to decay into smaller elements. The elements that remain after an atom decays are lighter than the original atom and are generally a different type of element.
5. In modern experiments, how much of a new element is generally created? How does the amount of the element and the time it exists affect the ability to study its properties?
These experiments might produce just milligrams of the material. Because of the small amounts generated and the short timeline, scientists have to study individual atoms of a new element instead of being able to study the properties of a larger sample. Scientists try to determine if the atoms in a new element behave as expected based on its place on the periodic table by putting the atoms in contact with other elements and observing what occurs.
Putting it all together
Answer the following questions as a class.
1. What are three ways that new elements are created? (Hint: Don’t forget to think about what happens to the labmade elements shortly after they are created.)
2. How does the energy required to create an atom relate to the atom’s size? What other factors might affect the type of element formed in a reaction?
3. Scientists in what fields are interested in how elements are created?
4. Why might we want to understand how elements are created?
5. What other questions do you have about the creation of elements?
Bonus: How does the size of an atom and particles within an atom compare with the size of the observable universe? Calculate the order of magnitude difference between their approximate diameters. Which do you think scientists know more about — atoms or the universe? Why? What are the limitations to studying each?