Download Section 4.4: Where did the elements come from?

Section 4.4: Where Did the Elements Come From?
Objectives:
1. Describe how the naturally occurring elements formed.
2. Explain how a transmutation changes one element into another.
3. Describe how particle accelerators are used to create synthetic elements.
Vocabulary: nuclear reaction, supernova, particle accelerators, superheavy element
Natural Elements

93 elements in the periodic table are found in nature. Most atoms of living things come from just six
elements: carbon, hydrogen, nitrogen, phosphorous, and sulfur. All of these elements were created in
the centers of stars billions of years ago, shortly after the universe was formed in a violent explosion
called the big bang.

Much of the evidence about the universe’s origin points toward a single event called the big bang, an
explosion of unbelievable violence. Before the big bang, all matter could fit inside a nucleus.

Right after the big bang, temperatures were so high that only energy could exist. As the universe
expanded, it cooled and protons and neutrons, and electrons condensed out of the energy. Further
cooling caused these particles to coalesce into hydrogen and helium atoms. Over time, huge clouds of
hydrogen formed, grew and pulled together due to the force of gravity between the particles. As the
clouds grew denser, the pressures and temperatures at the center of the clouds increased to the point
where nuclear reactions were initiated. At this point, stars were born. A star is a celestial body of hot
gases that radiates energy derived from nuclear reactions in their interior.

The nuclear reaction that occurs at the center of stars fuse isotopes of hydrogen
into helium atoms and in the process produces the energy that powers the star.
This energy comes from the fact that the mass of the helium atom is less than the
mass of the four hydrogen atoms. The “missing” mass is converted into a
massive amount of energy according to Einstein’s equation E=mc2, where m is
the missing energy, c is the speed of light (3 x 108 m/s) and E is the energy. This
energy causes temperatures inside stars to get high enough to fuse the helium
into elements as heavy as iron.

Massive stars (stars more than 100 times more massive than the Sun) create the elements that are
heavier than iron when they explode in massive explosions called a supernova. All the elements
heavier than iron on the periodic table are formed in this explosion. The stars contents shoot out into
space, where they can become part of newly formed star systems.
Transmutations

In the Middle Ages, many early scientists, called alchemists, tried to change, or transmute, ordinary
metals into gold. Modern chemistry grew out of the practice of alchemy. Early chemists such as John
Dalton had insisted that atoms never change into other elements. They did not realize that elements
can, in fact, change through a nuclear reaction that changes the number of protons in the nucleus.

Transmutations cannot be achieved by ordinary chemical means. In the 1910s, Ernest Rutherford
discovered that the nitrogen is transmuted to oxygen when nitrogen atoms are bombarded with alpha
particles.
Synthetic Elements

The discovery that transmutation can be cause to happen by bombarding various elements with alpha
particles has caused the discovery of many synthetic or manmade elements. To make them, one must
use special equipment called particle accelerators. The Fermi National Accelerator Laboratory in
Batavia, IL, just east of Chicago, has a circular accelerator which has a circumference of 4 miles.
Subatomic particles are accelerated through this ring to 99.9999% the speed of light.

Once the particles have been accelerated, they are made to collide with one another. Some of the
superheavy elements are created with such collisions. Superheavy elements are elements whose
atomic number is greater than 106. Most superheavy elements exist for only a tiny fraction of a second
because their nucleus has so many protons that they are not stable.