# Scales

Scales are color-coded lists of chemical elements based on different properties or classifications. Some scales are also clarified by scaling the element symbols in the periodic table.

### Standard atomic weight

Standard atomic weight as a dimensionless arithmetic mean of the relative masses of all isotopes of an element, weighted by their frequency on earth.

### Atomic mass

Mass of an atom of a chemical element in u, the atomic mass unit. The atomic mass is slightly less than the sum of the masses of its protons, neutrons and electrons due to the mass loss of binding energy.

The atomic radius provides an approximate determination of the spatial size of an element. The empirical atomic radius results from the observation of elements, i.e. from experiments and measurements.

The atomic radius gives an approximate determination of the spatial size of an element. Calculated values for atomic radii are determined by theoretical assumptions and calculations.

The covalent radius is defined as half the distance between two atoms of the same element that are covalently bonded. It depends on the type of bond (single, double, ...) and the electronegativity of the bonding partners.

The atomic radius named after Johannes Diderik van der Waals is based on the calculation of an imaginary hard sphere, which is used as a model for atomic behavior.

### Density

Density describes the ratio of a substance’s mass to its volume. It is independent of shape and size, but generally decreases with increasing temperature. It results from the masses of atoms and their distances from each other.

### Molar volume

The volume filled by 6.022·10²³ particles (Avogadro constant) of a substance.

### Speed of sound

The speed of sound indicates the speed at which sound waves propagate in a medium. It depends on the density of the substance, the pressure and the temperature.

### Melting point

The melting point corresponds to the conditions that exist during the phase transition of a substance from the solid to the liquid phase (melting). Unless otherwise stated, the boiling temperature is given under normal pressure of one atmosphere (101.325 Pa).

### Boiling point

The boiling point corresponds to the conditions that exist during the phase transition of a substance from the liquid to the gaseous phase (boiling). Unless otherwise stated, the boiling temperature is given under normal pressure of one atmosphere (101.325 Pa).

### Liquid range

The liquid range describes at distance between melting and boiling temperature of a substance; i.e., the temperature range in which a substance is in the liquid state. This value is calculated from the aforementioned phase transitions.

### Sublimation point

Sublimation describes the transition of a system from the solid to the gaseous state, without first liquefying. Unless otherwise stated, the boiling temperature is given under normal pressure of one atmosphere (101.325 Pa).

### Triple point

At the triple point, the temperature and pressure of three phases (gaseous, liquid and solid) are in thermodynamic equilibrium. Depending on the substance, different states of aggregation can exist at the triple point.

### Critical point

The critical point describes the extreme value of a phase boundary line (binodal), at which a substance undergoes a minimum or maximum of pressure and temperature. At this point, existing phases are fluids (individual particles can move freely in space).

### Transition temperature

Below the transition tempperature (also referred to as critical temperature), the substance is dominated by quantum mechanical effects and acquires superconducting properties.

### Melting enthalpy

Melting enthalpy refers to the amount of energy that must be expended to melt a sample at its melting point at constant pressure (isobaric).

### Enthalpy of vaporization

Enthalpy of vaporization refers to the amount of energy required to transform a certain amount of a liquid into the gaseous state (vaporization).

### Binding energy

The binding energy describes the amount of energy that must be supplied to a molecule to completely split its covalent bond. It depends on, among other things, the bond length, polarity and type of bond.

### Specific heat capacity

The specific heat capacity measures the ability of a substance to store thermal energy.

### Thermal conductivity

Thermal conductivity indicates the heat flow through a material. From this it can be derived how well a material conducts heat or how well it is suitable for thermal insulation.

### Expansion coefficient

The material-specific coefficient of expansion describes how much a material expands when the temperature changes due to supplied heat.

### Work function

Work function is the energy that must be applied to release an electron from an uncharged solid.

### Mohs hardness

Hardness test according to Friedrich Mohs: “hard substances scratch soft ones”. The hardness value can only be determined in comparison with other materials or material states. The ordinal scale (Mohs scale) is still in use in mineralogy and geology today. Minerals of Mohs hardness 1 to 2 are considered soft, from 3 to 5 as medium hard, and all minerals above Mohs hardness 6 are considered hard.

### Brinell hardness

The hardness test by Swedish engineer Johan August Brinell is used for soft to medium-hard metals and materials with uneven grain structure. A hard metal ball with a specified test force is pressed into the surface of the workpiece to be tested.

### Vickers hardness

The Vickers hardness test is used for testing homogeneous materials, thin-walled or surface-hardened workpieces and edge zones. The test is carried out by pressing an equilateral diamond pyramid into the workpiece.

### Young’s modulus

The material characteristic named after Thomas Young describes the proportional relationship between stress and strain during deformation of a solid body.

### Shear modulus

The shear modulus is an indicator given in GPa for the linear-elastic deformation of a component due to a shear force or shear stress.

### Bulk modulus

The bulk modulus describes the amount of pressure change needed to cause a certain volume change. It is an intensive, material-specific size from elasticity theory.

### Poisson’s ratio

Material characteristic named after Siméon Denis Poisson, which serves to calculate the deformation behavior of components under mechanical stress. It is also a measure of the compressibility of materials and one of the elastic constants of a material.

### Electrical conductivity

Electrical conductivity (given in Siemens per meter) is a physical property of a material that indicates how well it conducts electrical current.

### Resistance

Electrical resistance describes the required electrical voltage to allow a certain current to flow through an electrically conductive material.

### Reflectivity

Reflectivity is the ratio between reflected and incident intensity as an energy quantity.

### Refractive index

The dimensionless optical material property refractive index is the ratio of the wavelength of light in vacuum to the wavelength in the material.

### Standard potential

The electrode potential is the voltage that an electrode of an electrochemical cell delivers. If the normal hydrogen electrode is used as a reference, this voltage is referred to as standard potential.

### Pauling scale

Linus Pauling’s model as a measure of the ionic portion of the bond between two atoms is based on their electronegativity differences. Knowledge of experimentally determined bond dissociation energies is a prerequisite.

### Sanderson scale

R. T. Sanderson attributes electronegativity, like Albert Allred and Eugene Rochow, to the effective nuclear charge.

### Allred-Rochow scale

The scale according to the theory of Albert Allred and Eugene Rochow assumes that electronegativity is proportional to the electrostatic attraction exerted by the nuclear charge on the bonding electrons.

### Mulliken scale

Robert S. Mulliken calculates the electronegativity of the Mulliken scale named after him as the average of the ionization energy and the electron affinity.

### Allen scale

Leland C. Allen calculates electronegativity from the energy state of the valence electrons, which allows spectroscopic determination.

### Ghosh-Gupta scale

The electronegativity according to Dulal C. Ghosh and Kartick Gupta is a relative measure of the tendency of a chemical element to attract the electron pair of a bond. It is based on the polarizability of atoms and is given in electron volts.

### Boyd-Edgecombe scale

The method of measurement developed by Richard H. Boyd and Geoffrey C. Edgecombe is based on the assumption that the electronegativity of an atom depends on its ability to attract electrons in a chemical bond. It takes into account ionization energies and electron affinities.

### Nagle scale

A method for measuring electronegativity published by the chemist Jeffrey K. Nagle in 1990.

### Pearson absolute negativity

The scale developed by Ralph G. Pearson takes into account both the ionization energy and the electron affinity of an atom.

### Price

Average market prices per kilogram of a chemical element in US dollars. Market and daily deviations not calculated; data status before 2020.