Atomic structure refers to an atom’s composition – consisting of protons, neutrons, electrons and nucleus. Nucleus is the atom’s center portion, which hosts the positively-charged particle called proton; and also neutrons that don’t carry any charge or are neutral. Protons and neutrons are of almost the same weight; whereas electrons are way lighter. In fact, an electron is almost 2000 times lighter than protons or neutrons in mass. The protons and neutrons are commonly referred to as nucleons, and they make up 99.9 percent of an atom’s mass.
Electrons are negatively charged and their arrangement surrounds the nucleus, in energy or electron shells. This negative charge keeps the electron(s) attached to the nucleus’ positively charged proton, and therefore the electron(s) stay within the particular atom. The neutrons and protons, on the other hand, stay within the nucleus because of the nuclear force.
An atom’s chemical reactivity depends on its electrons. Also, the number of protons determine how likely the atom is to share its electrons. If the attraction between the protons and electrons are strong, the atom is less likely to share its electrons. When an atom shares its electron(s) with another atom, the two atoms bond with each other to become a molecule.
An atom does not carry any charge on its own. The electron and proton composition keeps it balanced or determines its electric charge – negative, positive, or neutral. A proton has a positive charge, and the electron is the opposite – it has a negative charge. A proton and electron have opposite charges, which are of the same magnitude. If the number of protons is more than electrons, then the atom has a positive charge. It’s negatively charged if the electron number is more than protons. In case, protons and electrons are present in equal proportion, it means the atom has a neutral electric charge.
The following table should offer some clarity on the different atomic particles and their weight and charge:
Constituent Electric Charge Mass (grams) Mass (Atomic Mass Unit)
Proton +1 1.6727 x 10-24 1.007316
Neutron 0 1.6750 x 10-24 1.008701
Electron -1 9.110 x 10-28 0.000549
Atomic mass unit is a unit used to determine an atomic particle’s mass. Since these particles are unbelievably light or minute, measuring their weight or mass in grams is not practically possible.
A nucleus is a very minute portion of an atom. In fact, it occupies far lesser space than a percent of the atom’s total footprint or volume. This means the electrons have a much larger space to move around the nucleus and they never encounter crowding issues, as a result. As aforementioned, electrons surround the nucleus in shells. These energy or electron shells can only house a specific number of electrons. The shell farthest from the nucleus is called the valence shell, and the electrons on this shell are called valence electrons.