# Chemistry: Atomic Structure and Chemical Bonding: Electromagnetic Radiations and Heisenberg՚s Uncertainty Principle (For CBSE, ICSE, IAS, NET, NRA 2022)

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• Electromagnetic radiation is a kind of energy, which is transmitted through space in the form of electric and magnetic fields. These do not require any medium to propagate. Visible light, radiant heat, radio waves, X-rays and gamma radiation are some of the examples of electromagnetic radiations.
• Amplitude: This refers to the maximum height to which the wave oscillates. It equals the height of the crests or depth of the troughs.
• Wavelength: It is the linear distance between two consecutive wave-crests or wave- troughs as. It is represented by a Greek letter lambda (λ) and is expressed in terms of m, cm, nm, or Angstrom ( = ) .
• Frequency: It is defined as the number of wave crests or wave troughs that pass-through a given point per second. It is represented by a Greek letter nu (ν) and is expressed in terms of (second inverse or per second) . It is also called as Hz (Hertz) .
• Wave number: It equals the number of waves per unit length. It is denoted as v (nu bar) and is equal to the reciprocal of the wavelength. The SI unit of v is (meter inverse) . However, sometimes it is also expressed as (centimeter inverse) .

## Heisenberg՚s Uncertainty Principle

• The principle states that for a particle it is impossible to know the exact position and momentum simultaneously.
• Heisenberg՚s principle questioned the validity of Bohr՚s model. It is so because according to Bohr՚s model we can precisely calculate the radius of the orbit (i.e.. , the position of the electron) and the velocity of electron in it. But it is not possible according to Heisenberg՚s principle.

## The Wave Mechanical Model – Orbitals

• Wave Mechanical Model of atom was proposed by Erwin Schrödinger- an Austrian physicist in 1926.
• Each electron circling an atom՚s nucleus occupies a specific orbital and spins a certain direction.
• According to this model, the motion of electron inside an atom could be described in terms of a mathematical function called, wave function, ψ (Greek letter, psi) . The orbital is like a cloud or the wave of energy.
• The wave functions are assumed to contain all the information about the electron and are obtained by solving a differential equation called Schrödinger wave equation (SWE) . The square of the wave function ψ2 is a measure of the probability of finding an electron in a three-dimensional space around the nucleus.
• Principle Quantum Number N Azimuthal Quantum Number l, Magnetic quantum number, is the three quantum numbers obtained Schrödinger wave equation (SWE) .

## Quantum Numbers

• A set of values describing the state of an electron including its distance from the nucleus.
• Quantum numbers also include the orientation and type of orbital where it is likely to be found, and its spin.
• There are a total four quantum numbers: the principal quantum number (n) , the orbital angular momentum quantum number (l) , the magnetic quantum number (ml) , and the electron spin quantum number (MS) .
• The principal quantum number, n describes the energy level (or principal shell) of the electron within the atom. Can have only positive non zero integral values (i.e.. , ) . This means that in an atom, the electron can have only certain energies. Thus, we may say that n quantizes energy of the electron. The principal quantum number also determines the mean distance of the electron from the nucleus, i.e.. , its size. Greater the value of n, farther is the electron from the nucleus.

## Types of Orbital (S, P, D, F) : Shapes of S, P and D Orbital Orbitals (S, P, D, F) : Shapes of S, P, and D Orbitals
• The four different types of orbitals (s, p, d, and f) have different shapes, and one orbital can hold a maximum of two electrons. The p, d, and f orbitals have different sublevels, thus can hold more electrons.
• The four different types of orbitals (s, p, d, and f) have different shapes, and one orbital can hold a maximum of two electrons. The p, d, and f orbitals have different sublevels, thus can hold more electrons. As stated, the electron configuration of each element is unique to its position on the periodic table.