Chemistry Notes Standard 1, Objective 1 Matter in the Universe

Chemistry Notes—Standard 1, Objective 1—Matter in the Universe

The big bang theory states that the universe began to expand about 14 billion years ago with the formation of the first few elements--hydrogen, helium, and a small amount of lithium. Over time, gravity caused these light elements to clump together into massive balls of gas. The pressure and density inside these bodies became so great that nuclear fusion began, causing the new stars to shine. Nuclear fusion in stars combines light elements together to make heavier elements. The more massive the star, the heavier the elements it can fuse. Massive stars eventually supernova, producing elements all the way up to at least number 98 (Californium), which has recently been detected in spectra from supernovae. New stars and new planets can form in these clouds of heavy elements. If the new stars are massive enough, they too will eventually supernova, enriching space with even more heavy elements. Over billions of years, multiple cycles of star birth and supernovae have enrichedthe universe with heavy elements.

Astronomers can tell what stuff in space is made of by studying the light coming from space. Each element produces or absorbs a unique spectrum of energy. So far, astronomers haven’t observed a spectrum for any new element out there in space that we don’t already have here on earth. As predicted by the big bang theory, astronomers find an abundance of hydrogen and helium in the universe. Hydrogen, helium and trace amounts of lithium are the only elements existing today thatmay have formed without the nuclear fusion process of stars. Hydrogen and helium make up roughly 98% of the standard matter in the universe. Even though stars have been forming heavier elements now for billions of years, elements heavier than helium still comprise only 2% of the standard matter in the universe. But without that 2% we wouldn’t be here.

Even though hydrogen and helium are abundant in the universe, these elements are relatively rare on earth. Smaller planets like earth don’t have enough gravity to hold down hydrogen and helium unless they are bonded to heavier elements. Any free hydrogen or helium that seeps out of earth’s interior simply floats off into space. Large planets such as Jupiter have enough gravity to hold down atmospheres of hydrogen and helium.

Relative abundance of elements in the earth’s crust.

Relative abundance of elements in our solar system.