Understanding Atomic Properties: Radius, Ionization, and More
Understanding Atomic Properties
Atomic Radius
Atomic radius is half the distance between the nuclei of two identical atoms bonded together.
Ionization Energy
Ionization energy is the minimum energy required for a neutral atom of an element in a gaseous state and in its ground electronic state to yield an electron in its outer level and lead to a monopositive ion, also in a gaseous state and in its ground electronic state. Ionization energy increases upwards and to the right on the periodic table.
Electron Affinity
Electron affinity is the energy exchanged in the process by which a neutral atom in its gaseous state and its ground electronic state receives an electron and becomes a mononegative ion, also in a gaseous state and in its fundamental state. Electron affinity increases downwards and to the left on the periodic table.
Electronegativity
Electronegativity is defined as the relative tendency of atoms to attract electrons from other atoms with which they are linked. Electronegativity increases upwards and to the right on the periodic table.
Electromagnetic Spectrum
The electromagnetic spectrum is made up of all electromagnetic waves arranged in order of frequency.
Atomic Emission Spectrum
The atomic emission spectrum is the radiation emitted by an element in a gaseous state when sufficient energy is communicated. The spectrum of sunlight is continuous, containing radiation at all frequencies. By contrast, the emission spectra of the elements are discontinuous. For example, elements in a gas emit only at certain frequencies.
A chemical element always gives the same spectrum, and no two elements have the same emission spectrum. Therefore, it is the fingerprint of the element.
Vision of the Hydrogen Spectrum
The hydrogen spectrum is the simplest of all and is composed of several series of bands, which appear in the ultraviolet, visible, and infrared regions.
Planck’s Quantum Theory
Planck’s quantum theory states that bodies emit or absorb energy in packets or quanta of energy.
Group Trends
In one group, with increasing atomic number, atomic radius increases. As the atomic number of the elements in a group increases, the number of occupied levels increases, while the effective nuclear charge on the outermost electron remains relatively constant. Therefore, the atomic radius increases.
Cations
Cations are smaller than the atoms from which they come. The lower number of electrons on the neutral atom results in lower shielding, and therefore, the outermost electron of the cation is subject to a higher effective nuclear charge. The radius of the cation is smaller than the neutral atom because the outermost electron is subject to a stronger nuclear attraction.
Anions
Anions are larger than the atoms from which they come. The anion is formed with more electrons than the neutral atom, so its shielding on its outermost electron is greater. As the nuclear charge is the same in both, the effective nuclear charge on the outermost electron is lower in the anion than in its corresponding atom. As a result, the radius of the anion is greater than the neutral atom.
Wave Motion
Wave motion is a form of energy transfer without net transport of material through the propagation of any form of disturbance. This disturbance is called a wave.
Mechanical Waves
Mechanical waves involve the propagation of a mechanical disturbance through a material medium for transmitting the mechanical energy of the wave. The material medium can be air, water, a rope, etc. A material medium is indispensable for the existence of the wave.
Electromagnetic Waves
Electromagnetic waves involve the transmission of electromagnetic energy through the propagation of two oscillatory fields, the electric and magnetic fields, which requires no physical medium, since they are periodic variations of the electric and magnetic state of space, and therefore also spread into space. An electromagnetic wave is characterized by amplitude (maximum displacement of a point on the upright), wavelength (distance between two consecutive similar points), frequency (number of vibrations per unit time), period (time taken to perform one complete vibration), and speed (with which the wave propagates).