What Is The Arrangement Of Particles In An Atom?

Atoms consist of particles called proton, neutron and electrons. Protons are positively charged while electrons are negatively charged particles. Neutrons do not hold a charge.

The protons and the neutrons are held together in the center of the atom. Together they make up the nucleus. The number of particles in the nucleus is called the nucleon number (also called the mass number) of the element. Due to the presence of protons, the nucleus is positively charged. The size of the nucleus is very small in relation to the whole atom.

Electrons orbit around the nucleus at great speeds. Each orbit has a specific energy level that allows a certain number of electrons to occupy it. These energy levels are called shells. Each shell is capable of holding up to a certain number of electrons. The shells are numbered from the nucleus outwards. The first shell can hold up to two electrons. It is called the duplet.

The second shell, called the octet, can hold eight electrons. The third shell can keep eighteen electrons. However, extra stability is gained if the third shell holds only eight electrons. Therefore, additional electrons go to the fourth shell, before the third shell is completely filled up.

The electrons in the outermost shell make up the valence electrons. These play a part in determining the chemical properties of the atom.