An atom is the smallest unit of matter with characteristic chemical properties of an element. The basic structure of an atom depicts three subatomic particles including the protons, neutrons, and electrons. The protons and neutrons have relatively equal mass and they reside within a dense nucleus cantered in the atom. However, the electrons occupy the orbits, which are also called the energy levels. Therefore, an atom is a unit of matter that contains protons, neutrons, electrons, nucleus, and orbits although the characteristic properties of the first three particles are described below.
The protons are positively charged particles while electrons are negatively charged. However, the neutrons have no charge attached to it. The electrons are found on the outermost regions of the atom, occupying the shells. The protons and neutrons have nearly equal mass, approximately 1.67 ×10 -24 grams (Anonymous, n.d). This is a concept of Dalton’s atomic theory, which gives the sub-particles their characteristic atomic mass unit. Although the masses are similar, they have unlike charges as previously described in this chapter. This implies that the number of neutrons in an atom gives the atom its mass.
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However, the electrons have a slightly smaller weight of only 9.11×10 -28 grams, which is represented by 1/1800 th of an atomic mass unit. Importantly, they still contribute to the atomic mass of the element (Anonymous, n.d). Conversely, it is crucial to exclude the mass of electrons when calculating the element’s atomic mass and instead, use only the number of protons and neutrons. The number of negative charges in an electron equals the number of positive charges in a proton. Therefore, in this case, the atom may be described as uncharged since the number of negative charges orbiting the nucleus equals the number of positive charges; hence, the net charge becomes zero. Finally, the number of atoms in an element describes its atomic number while the sum of protons and electrons gives the atom its mass number.
Reference
Anonymous, (n.d). Chapter 2: The structure of atoms. http://www.t.soka.ac.jp/chem/iwanami/intorduct/ch02structure.pdf
