Working with Physical Units

Added in version 1.1.0.

mendeleev integrates with pint to provide unit-aware access to physical properties. Append _u to any property name to get a pint.Quantity with proper units attached.

Quick Example

>>> from mendeleev import Fe, Al
>>> Fe.atomic_weight_u
55.845 dalton
>>> Al.density_u
2.7 gram / centimeter ** 3

That’s it — just add _u.

How It Works

When you access element.property_u, mendeleev:

  1. Strips the _u suffix to get the base property name.

  2. Looks up the unit in the PropertyMetadata database table.

  3. Multiplies the raw value by that unit using pint.

  4. Returns a pint.Quantity object.

If the property doesn’t exist, you’ll get an AttributeError. If it has no unit defined, you’ll also get an AttributeError. If the value is None (missing data), the _u version returns None too.

Basic Usage

Accessing properties with units

>>> from mendeleev import H, C, Fe
>>> H.atomic_weight
1.008
>>> H.atomic_weight_u
1.008 dalton
>>> C.density
2.267
>>> C.density_u
2.267 gram / centimeter ** 3

Without the _u suffix, you get raw numbers (just like before). With it, you get pint Quantity objects that know their units.

Unit Conversions

The returned Quantity objects support easy unit conversions:

>>> from mendeleev import Al, Fe
>>> Al.melting_point_u
933.47 kelvin
>>> Al.melting_point_u.to('celsius')
660.3199999999997 degree_Celsius
>>> Al.melting_point_u.to('fahrenheit')
1220.576 degree_Fahrenheit

>>> Fe.atomic_radius_u
126 picometer
>>> Fe.atomic_radius_u.to('angstrom')
1.26 angstrom

Calculations with Units

pint Quantities support arithmetic while preserving dimensional correctness:

>>> from mendeleev import Al
>>> from mendeleev.models import ureg

>>> # Mass = density × volume
>>> density = Al.density_u
>>> volume = 100 * ureg.milliliter
>>> mass = density * volume
>>> mass.to('gram')
270.0 gram

>>> from mendeleev import Fe
>>> # Convert electron affinity to joules
>>> Fe.electron_affinity_u.to('joule')
3.9342e-19 joule

The ureg (pint UnitRegistry) is available from mendeleev.models if you need to create new quantities for calculations.

Error Handling

Properties without units raise AttributeError:

>>> from mendeleev import H
>>> H.symbol_u
Traceback (most recent call last):
    ...
AttributeError: ...

Properties with None values return None:

>>> H.melting_point
None
>>> H.melting_point_u
None

Supported Classes

The _u suffix works on these model classes:

Properties with Units

Element properties with units

Atomic properties:

  • atomic_radius_u (pm) — Atomic radius

  • atomic_radius_rahm_u (pm) — Atomic radius by Rahm et al.

  • atomic_volume_u (cm³/mol) — Atomic volume

  • atomic_weight_u (Da) — Relative atomic weight

  • atomic_weight_uncertainty_u (Da) — Uncertainty in atomic weight

Abundance:

  • abundance_crust_u (mg/kg) — Abundance in Earth’s crust

  • abundance_sea_u (mg/L) — Abundance in seawater

Covalent radii:

  • covalent_radius_bragg_u (pm) — Bragg covalent radius

  • covalent_radius_cordero_u (pm) — Cordero covalent radius

  • covalent_radius_pyykko_u (pm) — Pyykkö single bond covalent radius

  • covalent_radius_pyykko_double_u (pm) — Pyykkö double bond covalent radius

  • covalent_radius_pyykko_triple_u (pm) — Pyykkö triple bond covalent radius

Van der Waals radii:

  • vdw_radius_u (pm) — Van der Waals radius

  • vdw_radius_alvarez_u (pm) — Alvarez VdW radius

  • vdw_radius_batsanov_u (pm) — Batsanov VdW radius

  • vdw_radius_bondi_u (pm) — Bondi VdW radius

  • vdw_radius_dreiding_u (pm) — Dreiding VdW radius

  • vdw_radius_mm3_u (pm) — MM3 VdW radius

  • vdw_radius_rt_u (pm) — RT VdW radius

  • vdw_radius_truhlar_u (pm) — Truhlar VdW radius

  • vdw_radius_uff_u (pm) — UFF VdW radius

Thermal properties:

  • boiling_point_u (K) — Boiling point

  • melting_point_u (K) — Melting point

  • critical_temperature_u (K) — Critical temperature

  • critical_pressure_u (MPa) — Critical pressure

  • triple_point_temperature_u (K) — Triple point temperature

  • triple_point_pressure_u (kPa) — Triple point pressure

  • evaporation_heat_u (kJ/mol) — Heat of vaporization

  • fusion_heat_u (kJ/mol) — Heat of fusion

  • heat_of_formation_u (kJ/mol) — Heat of formation

  • molar_heat_capacity_u (J/mol/K) — Molar heat capacity

  • specific_heat_capacity_u (J/g/K) — Specific heat capacity

  • thermal_conductivity_u (W/m/K) — Thermal conductivity

Physical properties:

  • density_u (g/cm³) — Density

  • lattice_constant_u (Å) — Lattice constant

  • metallic_radius_u (pm) — Metallic radius

  • metallic_radius_c12_u (pm) — Metallic radius (coordination 12)

Electronic properties:

  • dipole_polarizability_u (bohr³) — Dipole polarizability

  • dipole_polarizability_unc_u (bohr³) — Uncertainty in dipole polarizability

  • electron_affinity_u (eV) — Electron affinity

  • c6_u (hartree/bohr⁶) — C₆ dispersion coefficient

  • c6_gb_u (hartree/bohr⁶) — C₆ dispersion coefficient (Gould-Bučko)

  • hardness_u (eV) — Chemical hardness

  • softness_u (1/eV) — Chemical softness

Electronegativity scales:

  • electronegativity_allen_u (eV) — Allen electronegativity

  • electronegativity_allred_rochow_u (e²/pm²) — Allred-Rochow electronegativity

  • electronegativity_cottrell_sutton_u (e⁰·⁵/pm⁰·⁵) — Cottrell-Sutton electronegativity

  • electronegativity_ghosh_u (1/pm) — Ghosh electronegativity

  • electronegativity_gordy_u (e/pm) — Gordy electronegativity

  • electronegativity_li_xue_u (1/pm) — Li-Xue electronegativity

  • electronegativity_martynov_batsanov_u (eV⁰·⁵) — Martynov-Batsanov electronegativity

  • electronegativity_mulliken_u (eV) — Mulliken electronegativity

  • electronegativity_nagle_u (1/bohr) — Nagle electronegativity

  • en_gunnarsson_lundqvist_u (eV) — Gunnarsson-Lundqvist electronegativity

  • en_miedema_u (V) — Miedema electronegativity

  • en_robles_bartolotti_u (eV) — Robles-Bartolotti electronegativity

Chemical properties:

  • gas_basicity_u (kJ/mol) — Gas basicity

  • proton_affinity_u (kJ/mol) — Proton affinity

Economic properties:

  • price_per_kg_u (USD/kg) — Price per kilogram

  • production_concentration_u (%) — Production concentration

  • recycling_rate_u (%) — Recycling rate

  • reserve_distribution_u (%) — Reserve distribution

Miedema parameters:

  • miedema_molar_volume_u (cm³) — Miedema molar volume

Other classes with units

IonicRadius:

  • charge_u (e) — Ionic charge

  • crystal_radius_u (pm) — Crystal radius

  • ionic_radius_u (pm) — Ionic radius

IonizationEnergy:

  • ion_charge_u (e) — Ion charge

  • ionization_energy_u (eV) — Ionization energy

  • uncertainty_u (eV) — Uncertainty in ionization energy

Isotope:

  • mass_u (Da) — Isotopic mass

  • mass_uncertainty_u (Da) — Uncertainty in isotopic mass

  • quadrupole_moment_u (100 fm²) — Nuclear quadrupole moment

  • quadrupole_moment_uncertainty_u (100 fm²) — Uncertainty in quadrupole moment

PhaseTransition:

  • boiling_point_u (K) — Boiling point

  • critical_pressure_u (MPa) — Critical pressure

  • critical_temperature_u (K) — Critical temperature

  • melting_point_u (K) — Melting point

  • triple_point_pressure_u (kPa) — Triple point pressure

  • triple_point_temperature_u (K) — Triple point temperature

ScatteringFactor:

  • energy_u (eV) — Energy

See Also