Chapter 2:Unit 6. Electronic Arrangement in an Atom

Electronic Arrangement in an Atom

The goal of this section is to understand the electron orbitals (location of electrons in atoms), their different energies, and other properties. The use of quantum theory provides the best understanding to these topics. This knowledge is a precursor to chemical bonding.

The chemical properties of an element are determined by the number of electrons in an atom.

Inside the atom, electrons do not move randomly in space, instead an electron is confined to a specific region giving it a particular energy. The energy of the electrons is quantized. It means that it can be equal only to certain specific values and can jump from one energy level to another but not transition smoothly or stay between these levels.

The shells of an atom can be thought of concentric circles radiating out from the nucleus. The electrons that belong to a specific shell are most likely to be found within the corresponding circular area. Electrons occupy discrete energy levels (numbered 1,2,3 and so on) that contain subshells (s,p,d and f) and subshells consist of orbitals with the same name. These discrete energy levels are called principal energy level or shells. The further a shell is from the nucleus, the larger the volume becomes and more electrons it can hold and it contains more energy.

The lowest possible energy level is called ground state. Also, shells farther from nucleus are higher in energy and are called excited state. An orbital is a region of space within the subshell shell where the probability of finding electron is maximum.

Any s subshell contains only one “s”orbital, p subshell has three “p” orbitals, d subshell has five “d” orbitals and f subshell has 7 “f” orbitals. Each orbital can hold 2 electrons.

An s orbital has a sphere of electron density. It is lower in energy than other orbitals in the same shell. A p orbital has a dumbbell shape. A p orbital is higher in energy than a s orbital in the same shell, consequently d is higher in energy than p and f is higher in energy than d.( d and f orbitals not shown here). Any orbital can hold maximum two electrons of opposite spin. Since p subshell comes in set of three orbitals, they can hold maximum 6 electrons.

Find below the diagrams of different types of orbitals.

Watch the following video:

Questions:

1. How many total electrons can stay in n=4 level?

2. 1s orbital is larger than 2s orbital.
   a) True
   b) False

Ans: 1. 2.4²= 32 electrons

2.b) False