State how isotopes of an atom differ. All elements ar composed of tiny indivisible particles called atoms. Atoms of the same element are identical. The atoms of different atoms are different. Atoms of different elements can combine with one another in simple whole number ratios to form compounds.
Chemical reactions occur when atoms are separated, joined, or rearranged.
Atoms of one element are not changed into atoms of another by a chemical reaction. The discovery of electrons, protons, and neutrons caused a revision of the idea that atoms are indivisible. Today we know there are more than just these three subatomic particles. Electrons, protons, and neutrons are the building blocks of all atoms. Discovered by scientists studying the flow of electric current through gases at low pressure.