Home >> Science & Nature >> Science

What Are Two Ways That the Isotopes of an Element Are Different?

John Dalton revolutionized science with his atomic theory, that atoms are the building blocks of elements and that elements were made from identical atoms. Dalton's theory was not entirely correct, but it laid the groundwork for other scientific discoveries and insight into the atom and its structure. One error in Dalton's definition was his definition of an element. He thought that each element had to consist of exactly identical atoms. Scientists did not discover isotopes, which were made from slightly different atoms of the same element, until 1919, 75 years after Dalton died.

Atomic Structure
- Atoms compose every substance in the world. They are so small that only the most powerful electron microscopes can even catch a glimpse of them. But atoms are made up of still smaller particles. Protons reside in the nucleus of an atom, and electrons orbit the nucleus. Each of these elements carries an electric charge. Protons are positively charged, and electrons are negatively charged. Neutrons, which have a neutral charge, may also inhabit the atomic nucleus.
Atomic Number
- One way to classify different atoms is by their atomic numbers. The number of protons in an atom's nucleus is its atomic number. An atom with 12 protons in its nucleus has an atomic number of 12. Typically, an atom has the same number of electrons orbiting its nucleus as protons within the nucleus. This gives the atom a neutral atomic charge.
Element
- Elements are among the simplest forms of matter. Scientists once thought that an element was a substance made from identical atoms. This would mean that every atom in a particular element would be exactly identical to every other atom in that element. But the discovery of isotopes changed that definition. Now scientists define an element as a substance made entirely from atoms with the same atomic number. This means every atom of an element will have the same amount of protons but may have other variances.
Isotopes
- Isotopes of an element all have the same number of protons in the nucleus, but isotopes also have neutrons within the atomic nucleus. The number of neutrons in an atom's nucleus determines which isotope it is. For example, hydrogen has one proton, but when a neutron is added to the atom, it becomes the hydrogen isotope called deuterium. Two neutrons in the nucleus change it to tritium. But all three are still hydrogen.
Atomic Weight
- Protons and electrons differ in their electric charge, but they also differ greatly in weight. Electrons have negligible weight, but protons do have weight. Until the discovery of isotopes, scientists measured atomic weight simply by the amount of protons in its nucleus. Hydrogen has one proton, so its atomic weight was considered to be 1. But neutrons and protons have nearly identical weights. So hydrogen, deuterium and tritium have the same atomic number, since they all are types of hydrogen, but they all have different atomic weights.

Science