In 1913, Neil Bohr proposed a theory to explain the stability of an atom, where electrons revolved around the nucleus at certain energy levels. However, this does not happen and Rutherford’s model could not explain why the collapse does not occur. The loss of energy would ultimately slow down the electron speed and finally the electron would fall into the nucleus. But, according to the electromagnetic theory this would lead to continuous radiation of energy. His theory proposed electrons revolved in high-speed around positively charged nucleus. Rutherford compared his atom diagram to the solar system where the nucleus is like sun and the electron like the planets revolves around it. The volume of a nucleus was considered to be negligible compared to the volume of an atom. The number of electrons were equal to the number of protons and therefore, an atom is electrically neutral. Electrons revolve around the nucleus at a high-speed. This nucleus carries the entire mass of the atom. This conclusion helped him propose ‘Rutherford’s Atomic Model’.Īccording to his atom diagram, the atom has a small, positively charged nucleus in center. The nucleus is very small compared to the size of atom and the entire mass of an atom is centered in the nucleus. Thus, Rutherford could prove that the nucleus is positively charged, dense, and hard. Only few alpha particles rebounded after hitting the gold foil and this proved that the nucleus is very dense and hard. This center repelled the positively charged alpha particles and deflected them from their original path. This proved that there was a ‘center of positive charge’ in an atom. Next, he observed that some alpha particles were deflected through small and large angles. Protons are positively charged, electrons are negatively charged, while the neutrons carry no charge. The atomic model in the diagram below shows protons and neutrons concentrated at the atomic nucleus and electrons in the orbits surrounding it. This means the positive charge of protons and the negative charge of electrons cancel each other resulting in an electrically neutral atom. When one says an atom is electrically neutral, it means that the number of electrons equal the number of positive charges on the nucleus.

The center of an atom is the nucleus and one or more electrons surrounding the nucleus. Most of an atom is just empty space and consists of a positively charged nucleus of protons and neutrons surrounded by a cloud of negatively charged electrons. In this article, we familiarize you with the basic structure of an atom. However, today we all know that atoms exit. Then, unfortunately for the next 2000 years, this concept was lost and people only believed in four elements, earth, fire, air, and water. Atoms being the basic unit of matter was conceptualized way back in 500 BC when it was suggested by Greek philosopher Leucippus and his pupil Democritus. However, the model assumed electrons in the shells didn't interact with each other and couldn't explain why electrons seemed to stack in an irregular manner.An atom is the smallest building block of all matter made up of neutrons, protons, and electrons. It also explained why the noble gases were inert and why atoms on the left side of the periodic table attract electrons, while those on the right side lose them. For example, the shell model explained why atoms got smaller moving across a period (row) of the periodic table, even though they had more protons and electrons. The model explained some of the atomic properties of heavier atoms, which had never been reproduced before. Thus, the Bohr model for heavier atoms described electron shells. Once the level was full, additional electrons would be bumped up to the next level. Bohr believed each electron orbit could only hold a set number of electrons. More electrons were required to cancel out the positive charge of all of these protons. Heavier atoms contain more protons in the nucleus than the hydrogen atom.

Simple diagrams of atoms