What is an element (scientifically) and where did it come from?

Answer 1

An element is a pure substance that cannot be decomposed to a simpler substance by chemical means.

The idea arose in ancient times when Greek thinkers suggested that air, earth, fire, and/or water were elements. Alchemists in Europe and Arab countries discovered several "real" elements such as mercury, gold, and sulfur during the European middle ages. Until the 19th century, soda and potash were considered elements. Then some one passed an electric current through each and got sodium from soda and potassium from potash. So the test is: Can you decompose an "element" still further?

"Chemical means" rules out nuclear reactions in accelerators and reactors and transmutation of elements by radioactive decay.

Answer 2

An element is a substance composed of a single type of atom. All the atoms have the same number of protons and electrons, but the neutrons can differ in number. Atoms with different numbers of neutrons are known as isotopes.

All elements except Hydrogen were formed inside stars. In a star, Hydrogen atoms actually fuse together and form Helium. This is a physical process and not a chemical one, because a completely new atom is being formed. Chemistry studies the formation of new compounds, not new atoms. The Helium is then fused to form heavier elements like Carbon and Sodium. In ordinary fusion, Iron is the final step; however some stars explode as supernovas. This supplies enough energy to fuse heavier metals like Gold and Uranium.

Most of the universe is made of Hydrogen and it was the first element to form after the expansion of the universe began. For millions of years the universe was too energetic for atoms to form. There were only protons, neutrons and electrons moving freely around. At one point, the universe had expanded and cooled enough for the subatomic particles to come together, forming Hydrogen atoms and Hydrogen isotopes.