One of the main goals of the CSD model is that the datasets are self contained to simplify sharing of scientific data. An essential part of achieving this goal is that all quantities in a dataset are specified as proper scientific quantities, i.e. as a number and a unit. The use of quantities is integrated in all parts of CSDM.

The supporting material of the CSDM paper give an extended overview of the units and quantities allowed in CSDM. Here is a brief summary of the quantities allowed in CSDM. Note that the current JavaScript implementation does not give correct units of dimensionless units arising from ratios of quantities, such as the plane angle with dimensionality L/L.

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Test the unit parser here:

We are currently preparing generic libraries to handle quantities in other applications. You can see the status below.

Language	Implemented	Available	Comment
Python	😀	😀	The csdmpy package is available.
JavaScript	😀	😀	Debugging is still undergoing, but take a preview at gitlab.
Tcl	😀	😐	As part of the SIMPSON implementaion of CSDM, we are developing a Tcl interface that is still under development.
Obj-C	😀	😀	Units and quantities are supported by RMN and PhySyCalc. The libraries are not available for download.
C	😡	😡	We are planning to translate the JavaScript implementation into a C library. More information will become available here later.

😀: Fully implemented

😐: Partially implemented

😡: Not implemented

The entries of the table are the allowed quantities in CSDM.

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Quantity	SI unit	Dimensionality

As part of the quantities above, CSDM accepts a number of other physical symbols as listed in the table below.

Name	Symbol	Value in SI units

In 1916, ten years before the Schrodinger wave equation, G. N. Lewis suggested that a chemical bond involved sharing of electrons. He described what he called the cubical atom, because a cube has 8 corners, to represent the outer valence shell electrons which can be shared to create a bond. This was his octet rule.

1. Count the number of valence e^- each atom brings into the molecule.For ions, the charge must be taken into account.

   How many valence electrons in BeCl₂?

   How many valence electrons in NO₂^- and NO₂⁺?

2. Put electron pairs about each atom such that there are 8 electrons around each atom (octet rule), with the exception of H, which is only surrounded by 2 electrons. Sometimes it's necessary to form double and triple bonds. Only C, N, O, P and S (rarely Cl) will form multiple bonds.

   Draw the Lewis dot structure for CF₄.

   The number of valence electrons is 4 + 4 ( 7 ) = 32 electrons.

   So, we obtain:

   Draw the Lewis dot structure for CO.

   The number of valence electrons is 4 + 6 = 10 electrons or 5 pairs. Since both C and O allow multiple bonds we can still follow the octet and write:

3. If there is not enough electrons to follow the octet rule, then the least electronegative atom is left short of electrons.

   Draw the Lewis dot structure for BeF₂.

   In BeF₂ number of valence e^- = 2+ 2(7) = 16 e^- or 8 pairs. Since neither Be or F form multiple bonds readily and Be is least electronegative we obtain:

4. If there are too many electrons to follow the octet rule, then the extra electrons are placed on the central atom.

   Draw the Lewis dot structure for SF₄.

   In SF₄ the number of valence electrons is 6 + 4 ( 7 ) = 34 electrons or 17 pairs. Placing the extra electrons on S we obtain:

How can the octet rule be violated in this last example? The octet rule arises because the s and p orbitals can take on up to 8 electrons. However, once we reach the third row of elements in the periodic table we also have d-orbitals, and these orbitals help take the extra electrons. Note that you still need to know how the atoms are connected in a polyatomic molecule before using the Lewis-Dot structure rules.

Homework from Chemisty, The Central Science, 10th Ed.

Psycalc

8.45, 8.47, 8.49, 8.51, 8.53, 8.55, 8.57, 8.59, 8.61, 8.63