Fix unit for Element properties: density_of_solid and Molar volume

[DanielYang59]

Summary

• Remove unit in docstring for Element properties, to close Units in docstring appear to be wrong for density_in_solid #4453
• Check other units in docstring

[DanielYang59]

This could be breaking.

These two units are exactly the same but feels like MPa might be more common than MN m^-2 (also more consistent with docstring and other hardness)?

pymatgen/src/pymatgen/core/periodic_table.py

Lines 107 to 112 in f9d9fe8

	bulk_modulus (float, optional): Bulk modulus (GPa).
	youngs_modulus (float, optional): Young's modulus (GPa).
	brinell_hardness (float, optional): Brinell hardness (MPa).
	rigidity_modulus (float, optional): Rigidity modulus (GPa).
	mineral_hardness (float, optional): Mohs hardness.
	vickers_hardness (float, optional): Vickers hardness (MPa).

[DanielYang59]

I have no strong opinion on this, I originally thought we just remove all units from the docstring if it's a scalar and redirect people to get the unit from FloatWithUnit, but feels like it's not good for docstring clarity as most data for ptable wouldn't be updated very often, also many units are pretty much "singleton" (e.g. K for temperature, angstrom for radii,...):

pymatgen/src/pymatgen/core/periodic_table.py

Lines 84 to 116 in f9d9fe8

	Attributes:
	Z (int): Atomic number of the element.
	symbol (str): Element symbol (e.g., "H", "Fe").
	long_name (str): Full name of the element (e.g., "Hydrogen").
	A (int, optional): Atomic mass number (sum of protons and neutrons).
	atomic_radius_calculated (float, optional): Calculated atomic radius (Å).
	van_der_waals_radius (float, optional): Van der Waals radius (Å).
	mendeleev_no (int, optional): Mendeleev number based on crystal-structure maps.
	electrical_resistivity (float, optional): Electrical resistivity (Ω·m).
	velocity_of_sound (float, optional): Velocity of sound (m/s).
	reflectivity (float, optional): Reflectivity (%).
	refractive_index (float, optional): Refractive index.
	poissons_ratio (float, optional): Poisson's ratio.
	molar_volume (float, optional): Molar volume (cm³/mol).
	electronic_structure (str): Electronic structure (e.g., "[Ar].3d6.4s2").
	atomic_orbitals (dict): Orbital energies (Hartree units).
	atomic_orbitals_eV (dict): Orbital energies in electron volts (eV).
	thermal_conductivity (float, optional): Thermal conductivity (W/m·K).
	boiling_point (float, optional): Boiling point (K).
	melting_point (float, optional): Melting point (K).
	critical_temperature (float, optional): Critical temperature (K).
	superconduction_temperature (float, optional): Superconducting transition temperature (K).
	liquid_range (float, optional): Temperature range for liquid phase (K).
	bulk_modulus (float, optional): Bulk modulus (GPa).
	youngs_modulus (float, optional): Young's modulus (GPa).
	brinell_hardness (float, optional): Brinell hardness (MPa).
	rigidity_modulus (float, optional): Rigidity modulus (GPa).
	mineral_hardness (float, optional): Mohs hardness.
	vickers_hardness (float, optional): Vickers hardness (MPa).
	density_of_solid (float, optional): Density in solid phase (g/cm³).
	coefficient_of_linear_thermal_expansion (float, optional): Thermal expansion coefficient (K⁻¹).
	ground_level (float, optional): Ground energy level of the element.
	ionization_energies (list[Optional[float]]): Ionization energies (kJ/mol), indexed from 0.