CHM 101 Modern Electronic Theory of Atoms PDF 2024

CHM 101. Modern electronic theory of atoms. Electronic configuration, periodicity, and building up of the periodic table The modern electronic theory of atoms is a fundamental concept in chemistry and physics that explains the structure and properties of atoms and essential for grasping various che...

CHM 101. Modern electronic theory of atoms. Electronic configuration, periodicity, and building up of the periodic table The modern electronic theory of atoms is a fundamental concept in chemistry and physics that explains the structure and properties of atoms and essential for grasping various chemical and physical phenomena, including chemical bonding, periodic trends, and the behavior of electrons in atoms. The following Key Components of the Modern Electronic Theory 1. Atomic Structure The modern electronic theory describes an atom as consisting of three main components: protons, neutrons, and electrons. Protons and neutrons reside in the nucleus, which is the central part of the atom. The protons have a positive charge, while the neutrons are neutral. The electrons, on the other hand, are negatively charged and occupy specific energy levels or shells around the nucleus. The table below summarizes the properties of these three subatomic particles. Name of Symbol Mass (approx.. in Charge Particles Kg) Proton P⁺ 1.6 × 10-27 1+ -27 Neutron n, n⁰ 1.6 × 10 none Electron e⁻ 9.1 × 10-31 1- The modern theory went further to explain that atoms of one element are the same, while atoms of different elements are different. The fundamental characteristic that all atoms of the same element share is thenumber of protons. All atoms of hydrogen have one and only one proton in the nucleus; all atoms of iron have 26 protons in the nucleus. This number of protons is so important to the identity of an atom that it is called the atomic number of the element. Thus, hydrogen has an atomic number of 1, while iron has an atomic number of 26. Each element has its own characteristic atomic number. Atoms of the same element can have different numbers of neutrons, however. Atoms of the same element (i.e., atoms with the same number of protons) with different numbers of neutrons are called isotopes. Most naturally occurring elements exist as isotopes. For example, most hydrogen atoms have a single proton in their nucleus. However, a small number (about one in a million) of hydrogen atoms have a proton and a neutron in their nuclei. This particular isotope of hydrogen is called deuterium. A very rare form of hydrogen has one proton and two neutrons in the nucleus; this isotope of hydrogen is called tritium. The sum of the number of protons and neutrons in the nucleus is called the mass number of the isotope. 2. Electron Shells and Subshells Electron shells are the energy levels that electrons occupy around the nucleus. These shells are further divided into subshells, which are designated by the letters s, p, d, and f. Each subshell has a specific capacity for electrons, and the arrangement of electrons in these subshells determines the chemical properties of an element. Characteristic of Shells The principal quantum number is denoted by ‘n’. It represents the name, size and energy of the shell to which the electron belongs. The value of n lies between 1 to ∞. Shells The maximum number of electrons present in the shell on the 2n2 rule. Name of Shell The value of ‘n’ Maximum electrons present (2n2) K 1 2 L 2 8 M 3 18 N 4 32 Subshell All the electrons having the same shall do not have the same energy. Based on the energy of the electrons, the shells are divided into sublevels or subshells. Each shell is composed of one or more subshells, which are themselves composed of atomic orbitals The subshells are described with the help of Azimuthal quantum numbers (l). The value of l‘’ depends upon the value of the shell (n) with which it is associated. These subshells have been designated as s (l = 0), p (l =1), d (l = 2) and f (l =3). The energies of the various subshells in the same shell are in the order s < p < d