Fundamentals of Atomic Structure

 The smallest particle of matter which cannot be further divided and holds its identity as a chemical element is termed as an Atom. All matter such as solids, liquids, or gases is made up of molecules, and all atoms associates to form molecules. For example, water molecules are made up of hydrogen and oxygen atoms.

Particles of Atom

An atom consists of protons, electrons, and neutrons.   The center part of an atom is named the nucleus and it consists of neutrons and protons. Fig.1 shows the structure of an atom. As per Bohr’s model, the electrons are assigned to shells or orbits that are arranged concentrically around the nucleus and with different energy levels. There is almost a maximum of seven levels of shells to hold more electrons and the electrons in the outermost orbit are called Valence Electrons. Based on the arrangements and atomic number, atoms exhibit different properties. Almost protons and neutrons are having an equal atomic mass of 1.67X10^-24 g which is defined as Dalton or atomic mass unit (amu) but the mass of electrons is very much smaller than the protons and it weighs about 9.11 X 10^-28. When compared to electrons the neutrons provide many contributions to the overall atomic as of an element. Thus, while calculating the atomic mass of an element only the mass of Protons and Neutrons are considered whereas the mass of electrons is almost ignored.

Being a negative charge and positive charge, the electrons and protons are responsible for the charge of an atom; on the other hand, the neutron has no charge. The positive and negative charges may be defined as +1 and -1 respectively. Since the amount of protons existing in the nucleus is equal to the number of electrons in the orbits, the atom becomes neutral and it has no net charge. All the atoms try to grasp the electron octet by filling the outermost shell with eight electrons. Thus the element with fewer electrons in the outer orbit can release electrons and the element with many numbers of outer electrons can accept additional electrons.

The atomic number is the number of protons present in an element. For illustration, as the amount of protons found in the Carbon atom is 6, the atomic number of carbon is said to be 6. Whereas elements are said to be Ions if the atoms of the equivalent elements are having a dissimilar quantity of electrons.

In contrast, Isotopes are the ones in which the atoms of the similar elements are having a different number of neutrons. The Mass number is the combination of the number of protons and neutrons present in an atom. The neutrons accumulated in an atom can be found simply by deducting the number of protons from mass number. By considering the isotopes of the same element, it has an equal atomic number but an unequal mass number. For instance, the isotopes of carbon are ⁶C₁₂ and ⁶C₁₃, whose atomic number is 6 and the mass number of 12 and 13 respectively.

All the available elements are listed in the periodic table as in Fig.3 with increasing atomic number and it is dived into periods with main and subgroups. The period denotes the main groups, subgroups, the number of orbits, and the number of electrons in the outermost orbit. Group 1 to 2 and 13 to 18 form the main groups and groups 3 to 12 forms the subgroups. The left side of the periodic table consists of metals, semimetals, and nonmetals. Metals have the drive to contribute valence electrons to attain configuration of noble gas whereas the non-metals tend to absorb electrons to realize structure noble gas. Amidst, there are semimetals namely silicon and germanium.

Chemical Bonds

From the periodic table, it could be observed that the elements in group 8 are monoatomic gases also called inert gases which have the special property of generally not reacting with other elements. On the other hand, other gaseous elements that occur as diatomic gases are very much reactive. Now, we can think of why some of the atoms are very much reactive and it interacts with each other? The reason for this question may be explained in detail by getting into the concept of bonding of atoms. The types of bonds that exist within the elements are covalent bonds and ionic bonds. These types of bonding will be discussed in detail below.

Covalent Bond

The type of bond is realized in non-metals. To accomplish the octet of electron non-metals forms this bond. For instance, Fluorine has an atomic number of 9 and it consists of 7 valence electrons. Thus, two fluorine atoms can share one electron to get into the state called octet of electrons. The main reason behind the formation of atomic bonds in the element is always attempting to attain the minimum energy level by nature. Since the atoms strive to reach filled outer shell, the elemental atoms of Fluorine, Nitrogen, Oxygen, Chlorine, Iodine, and Bromine never seems to be a solo atom but constantly exists as molecule F₂, N₂, O₂, Cl₂, I₂ and Br₂.

Fig. 4 shows the atomic bond of silane. In this structure, it could be observed that the silicon atom reaches the electrons of the octet and the hydrogen atom achieves the fulfilled outermost shell with 2 electrons.

Ionic Bond

Because of the combination of metals and non-metals Ionic bond is formed as shown in Fig.5. In this progression, the metals provide electrons to achieve the filled outer shell, whereas the non-metals accept the electrons. NaCl is the best example of an ionic bond. Here, the sodium atom gives one valence electron and becomes positively charged while the chlorine atoms admit one electron to become negatively charged.

The type of bonding other than these types is inter-molecular bonding that is mainly due to the load-displacement that ends with attraction and repulsion of particles. Thus, in this article, a brief account of the basic structure of the atom and its properties has been explained. As the atomic structure of the element is the most important concept behind all engineering concepts, everyone must understand the concept clearly which will explore us to learn other relevant concepts with better understanding.