7.1 - From Classical Physics to Quantum Theory
We must first grasp the nature of waves to comprehend Planck's quantum theory.
A wave is a vibrating disturbance via which energy is conveyed.
The distance between similar spots on successive waves is measured in wavelength.
The number of waves that travel through a specific place in one second is known as the frequency v (nu).
The vertical distance between a wave's midline and its peak or trough is called amplitude.
An electromagnetic wave has an electric field component and a magnetic field component, according to Maxwell's theory.
The emission and transfer of energy in the form of electromagnetic waves are known as electromagnetic radiation.
The smallest amount of energy that may be emitted in the form of electromagnetic radiation was given the name quantum by Planck.
7.2 - The Photoelectric Effect
The photoelectric effect is a process in which electrons are ejected from the surface of certain metals when they are exposed to light with a minimum frequency, known as the threshold frequency.
The lightwave theory is a hypothesis that describes how light travels through space.
Einstein, on the other hand, made a remarkable assumption.
He proposed that a light beam is a stream of particles. Photons are the new name for these light particles.
7.3 - Bohr’s Theory of the Hydrogen Atom
Physicists have looked into the properties of emission spectra, or the continuous or line spectra of radiation released by substances.
Energizing a sample of the material with thermal energy or another source of energy can reveal a substance's emission spectrum.
Light emission at specific wavelengths is represented by line spectra.
When n = 1, which corresponds to the highest stable energy state, the most negative value is reached.
This is referred to as the ground state or ground level, and it relates to a system's lowest energy state.
For n = 2, 3, Each of these levels is referred to as an aroused state or excited level since it is more energetic than the ground state.
7.4 - The Dual Nature of the Electron
An electron bound to the nucleus, according to de Broglie, acts as a standing wave.
Some spots on the string, known as nodes, do not move at all, implying that the wave amplitude at these points is 0.
7.5 - Quantum Mechanics
Werner Heisenberg developed the Heisenberg uncertainty principle, which states: It is impossible to know the momentum p and the position of a particle with certainty at the same time.
The wave function of an electron in an atom is known as an atomic orbital.
7.6 - Quantum Numbers
Three quantum numbers are necessary for quantum mechanics to represent the distribution of electrons in hydrogen and other atoms.
These figures are derived from the Schrödinger equation's mathematical solution for the hydrogen atom.
The main quantum number, the angular momentum quantum number, and the magnetic quantum number are the three types of quantum numbers.
These quantum numbers will be used to characterize atomic orbitals as well as to identify electrons that live within them.
7.7 - Atomic Orbitals
The p orbitals begin with the primary quantum number n = 2 as should be obvious.
There is only a 1s orbital if n = 1. The angular momentum quantum number l can only take the value zero if n = 1.
When l = 2, there are five different ml values, each of which corresponds to a different d orbital. For a d orbital, the lowest value of n is 3.
7.8 - Electron Configuration
To understand electronic behavior in many-electron atoms, however, we must first understand the atom's electron configuration, or how the electrons are distributed throughout the many atomic orbitals.
The Pauli exclusion principle is used to determine electron configurations in many-electron atoms.
No two electrons in an atom may have the same set of four quantum numbers, according to this concept.
The term "paramagnetic" refers to materials that have net unpaired spins and are attracted to a magnet.
Diamagnetic materials have no net unpaired spins and are somewhat repelled by magnets.
7.9 - The Building-Up Principle
According to the Aufbau principle, as protons are added one by one to the nucleus to form the elements, electrons are similarly added to the atomic orbitals.
Except for hydrogen and helium, the electron configurations of all elements are represented by a noble gas core
which displays in brackets the noble gas element that most nearly precedes the element in question, followed by the symbol for the highest filled subshells in the outermost shells.
Transition metals either have partially full d subshells or quickly produce cations with partially filled d subshells.