Where Did the Elements Come From?

Natural Elements

• There are 93 naturally occurring elements • All are found on Earth except for Technetium,

Promethium, and Neptunium which have been detected in the spectra of stars.

• Most atoms in living things come from six elements: carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur

• It is believed all 93 elements were created in the centers of stars billions of years ago.

Big Bang Theory

• An explosion of unbelievable violence, before which all matter in the universe could fit on a pinhead.

• Most scientists accept this model for the universe’s beginning

• When the universe had expanded and cooled enough the electrons, protons, and neutrons that were formed came together to form hydrogen and helium atoms

Formation of Stars

• Huge hydrogen clouds were pulled closer and closer by gravity.

• As the clouds became more dense the temperature and pressure at the center of the clouds increased and stars were born.

• Nuclear reactions took place in the center of the stars these reactions are the same as those that take place in stars today

• Fusion of hydrogen nuclei into helium atoms is one of the simplest nuclear reactions

Nuclear Fusion

• 4 Hydrogen nuclei containing 1 proton each combine to form a Helium atom which is composed of 2 protons and 2 neutrons.

• The mass of the hydrogen nuclei is greater than the mass of the helium nucleus, but the mass is not lost rather it is converted to energy, ie. Einstein’s law of relativity E=mc2 where E is energy, m is the mass being “lost” and c is the speed of light.

• The energy produced by nuclear fusion is so great it keeps the center of stars at a very high temperature.

Other Atoms Formed by Fusion

• Because of the high temperatures in stars the helium nuclei fuse to form a berylium nucleus.

• A helium nucleus and a berylium nucleus fuse to form a carbon nucleus.

• Repeated fusion reactions form elements as massive as iron

Production of elements heavier than iron

• When very massive stars have converted almost all of the hydrogen and helium in its core into heavier elements up to iron, the star collapses, and then blows apart producing the elements heavier than iron.

• This explosion is called a supernova.

• The contents of the star become part of a newly forming star system.

Transmutation

• Transmutations are nuclear changes that change one atom into another.

• This cannot be accomplished in ordinary chemical reactions.

• The first transmutation to be documented was that of nitrogen becoming oxygen when struck by an alpha particle and adding a proton to the nitrogen atom.

Synthetic Elements

• Synthetic or man made elements are produced by a particle accelerator.

• Transuranium elements those with more than 92 protons are synthetic

• Cyclotron produces energy pulses one after another causing charged particles to accelerate faster and faster until particles collide and fuse to form atomic nuclei with higher atomic numbers

Particle accelerators cont.

• When particles reach 1/10th the speed of light it gains enough energy that it also gains mass according to E= mc2.

• As the particle becomes more massive it slows down and misses the next energy impulse to accelerate it.

• The cyclotron can only be used to create atoms with atomic numbers up to 106

Synchrotron

• The synchrotron is used to make superheavy elements, elements with atomic numbers greater than 106

• The energy pulses are timed to match the acceleration of the particles so they will continue to accelerate.

• Particle accelerators are very large the one in Batavia, IL is 4 miles in circumference.

• Particles are accelerated through the accelerator to 99.9999% the speed of light.

Life of a Superheavy Element

• Only a few nuclei are produced by a synchrotron and they last for only a fraction of a second.

• There is controversy over whether some elements have actually been created by using particle accelerators