Properties (Molecular Weight)

Description

This article describes a method for retrieving the molecular weight of chemical compounds.

Model theory

Table 1. Atomic weight.

Element	Atomic weight (g/mol)
Ac	227
Ag	107.8682
Al	26.9815384
Am	243
Ar	39.948
As	74.921595
At	210
Au	196.96657
B	10.811
Ba	137.327
Be	9.0121831
Bi	208.9804
Bk	247
Br	79.904
C	12.0107
Ca	40.078
Cd	112.414
Ce	140.116
Cf	251
Cl	35.453
Cm	247
Co	58.933194
Cr	51.9961
Cs	132.90545196
Cu	63.546
Dy	162.5
Er	167.259
Es	252
Eu	151.964
F	18.998403163
Fe	55.845
Fm	257
Fr	223
Ga	69.723
Gd	157.25
Ge	72.63
H	1.00794
He	4.002602
Hf	178.486
Hg	200.592
Ho	164.930328
I	126.90447
In	114.818
Ir	192.217
K	39.0983
Kr	83.798
La	138.90547
Li	6.941
Lr	262
Lu	174.9668
Md	258
Mg	24.305
Mn	54.938043
Mo	95.95
N	14.0067
Na	22.98976928
Nb	92.90637
Nd	144.242
Ne	20.1797
Ni	58.6934
No	259
Np	237
O	15.9994
Os	190.23
P	30.973761998
Pa	231.03588
Pb	207.2
Pd	106.42
Pm	145
Po	209
Pr	140.90766
Pt	195.084
Pu	244
Ra	226
Rb	85.4678
Re	186.207
Rh	102.90549
Rn	222
Ru	101.07
S	32.065
Sb	121.76
Sc	44.955908
Se	78.971
Si	28.0855
Sm	150.36
Sn	118.71
Sr	87.62
Ta	180.94788
Tb	158.925354
Tc	98
Te	127.6
Th	232.0377
Ti	47.867
Tl	204.3833
Tm	168.934218
U	238.02891
V	50.9415
W	183.84
Xe	131.293
Y	88.90584
Yb	173.045
Zn	65.38
Zr	91.224

This function returns the molecular weight of a chemical compound based on the atomic weights of its constituent elements.

The following applies to use of the molecular weight function:

• The atomic weights of the elements which are used by the function are presented in Table 1.
• Only alphanumeric characters are allowed in the molecule definition
• Only stoichiometric (integer) counts of elements are permitted; no fractions or decimals
• Bracket notation is permitted
• Nested brackets are permitted
• Dot notation is not permitted; use brackets instead

Excel

The molecular weight calculation may be invoked from the Excel formula bar with the following function call:

=mdProps_MW(Formula as String, Optional returnElementCount as Boolean = false)

Invoking the function with no arguments will print Help text associated with the model, including a link to this page.

The input parameters and calculation results are defined below in matrix notation, along with an example image showing the selection of the same cells and arrays in the Excel interface:

${\begin{aligned}{\mathit {Formula}}&={\big [}s_{\rm {m}}{\big ]}\\{\mathit {returnElementCount}}&={\big [}{\text{(True/False)}}{\big ]}\\\end{aligned}}$ ${\mathit {mdProps\_MW}}={\begin{bmatrix}{\rm {MW}}{\text{ (g/mol)}}\\{s_{\rm {e}}}^{*}\\\end{bmatrix}}$ where: $s_{\rm {m}}$ is a string of characters representing the molecular formula of the substance ${\mathit {returnElementCount}}$ indicates whether to return a stoichiometric count of each element identified in the molecular formula (default is to omit) ${\rm {MW}}$ is the molecular weight of the substance (g/mol) $s_{\rm {e}}$ is a string of characters representing the stoichiometric count of each element identified in the molecular formula the $^{*}$ superscript denotes an optionally-returned result

Figure 1. Example showing the selection of the input parameters (shaded blue frame), and Results (light blue frame) array in Excel. The parameter ${\mathit {returnElementCount}}={\text{True}}$ in this example.