Demicritus was a Greek philosopher around 400 B.C. Demicritus discovered that matter could not be divided into smaller pieces forever. This was his atomic theory, which is what we call the Greek Model. This was the first “unofficial” atomic theory. John Dalton was an English chemist who proposed the first atomic theory(Dalton Model). He stated that all elements are made up of indivisible particles. Atoms of the same element are exactly alike, and elements of different elements are different. Also that compounds are formed by two or more atoms joining together of different elements. JJ Thomson was an English scientist who discovered the atom in 1897. Thomson said that the atom was made of positively charged material with negatively charged electrons scattered through it. This is sometimes called the �

Only ion stream B makes it right through the machine to the ion detector. The other ions collide with the walls where they will pick up electrons and be neutralized. Eventually, they get removed from the mass spectrometer by the vacuum pump.

Isotopes are different atoms of the same element that have different numbers of neutrons. About seventy five percent of elements in nature have isotopes mixtures. The abundance of isotopes of an element is the same throughout nature. In all natural samples of Li, 7.42% of the atoms are 6 Li and the remaining 92.58% are 7Li. In all natural samples of Cu, 69.17% of the atoms are 63Cu and the remaining 30.83% are 65Cu. This is relative to the periodic table because the atomic mass is the weighted average mass of the naturally occurring element. Atomic mass=fractionA + fractionB.

Some topics in this essay:
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