This means that atoms of the same element must have the same number of protons, but may have different numbers of neutrons, and consequently differentĪtomic weights. The atomic number, which definesĪ given element, consists solely of the number of protons in the nucleus. Scientists define the atomic mass to be the total number of protons and neutrons. The nucleus is so small compared with the rest of the atom, almost all of the mass of the atom is located there. Protons and neutrons have similar masses, and are about 1,800 times heavier than electrons. This means that if the nucleus was the same size as Earth, the radius of the atom would stretch all the way to the sun.

The nucleus is only about 10-12 cm across, while the atom itself is about 10-8 cm. The nucleus is made up of protons and neutrons and makes a tiny fraction of the overall size of the atom. Current models of the structure of the atom consist of a small and relatively heavy nucleus Yet scientists realized that these atoms are themselves are made up of even smaller particlesĪnd at an even smaller scale, scientists now know that neutrons and protons are composed of tiny fundamental particles called quarks. For this reason, they are often considered to be the building blocks of nature. The smallest possible unit of any given element.

An atom is a piece of matter that cannot be broken down into smaller units by chemical means, giving The early twentieth century, when the existence of atoms became widely accepted thanks to the work of Albert Einstein. The composition of these elements was a matter of speculation until Manhattan Project: Science > The Atom and Atomic Structureīy the nineteenth century chemists had recognized that the wide variety of materials that they studied were mixtures of basic, elementary substances.

Atomic structure