The Descriptive Properties Section of the Elements Chapter contains properties used to identify and characterize element entities. The section contains six fields: symbol field; periodic group field; valences field; electrons field; atom number field; atomic weight field.

The Element's Symbol field contains the identifier commonly found in chemical formulae and molecular structures. It is typically a text string less than three characters in length.

Element	Symbol	Structure
Carbon	C
Hydrogen	H
Nitrogen	N
Oxygen	O

You edit the element Symbol field like other text fields. Clicking the left mouse button on the field's value control activates the edit dialog. See the documentation for the Text-Reference Edit dialog for editing details.

The element Group field represents the element's column in the periodic table. Although this field may contain any text value, the values provided by Molecular Knowledge Systems use the modern numbering system, i.e., values 1 through 18.

You edit the element group field like other text fields. Clicking the left mouse button on the field's value control activates the edit dialog. See the documentation for the Text-Reference Edit dialog for further editing details

The element group field is currently used for information purposes only. However, periodic groups are sometimes used to identify alternate groups when contributions are missing in group contribution techniques. For example, if a technique is missing a -AsH2 group, one might try substituting the contribution for the -PH2 group or the -NH2 group if that one was missing. All this group substitutions use alternate elements from group 15 of the periodic table.

The element Valences field is used by Cranium and Synapse when atoms are bonded together in chemical and group molecular strctures. For example, when you add a carbon atom to a structure editor pane, the application looks up the valece of carbon, which is 4, and adds that many hydrogen atoms to satisfy the valence.

Valences are always entered as positive numbers. Thus, the valence for calcium is 2 and the valence for oxygen is also 2.

An element may have up to nine valences. Some elements with multiple valences are shown here:

Element	Symbol	Valences
Americium	Am	3, 4, 5, 6
Bismuth	Bi	3, 5
Chlorine	Cl	1, 5, 7
Germanium	Ge	2, 4
Indium	In	1, 2, 3
Nitrogen	N	3, 5
Sulfur	S	2, 4, 6
Tin	Sn	2, 4

Cranium and Synapse will not allow you to enter a molecular structure whose atoms do not satify each element's valence. Thus, to enter the molecular structure of certain chemicals it may be necessary to change an element's valences. For example, by default xeon has a valence of 0 (zero). To enter xenon hexafluoride (XeF6), it is necessary to add a valence of 6 to xenon. Once you enter xenon hexafluoride's molecular structure, you can, if you wish, remove this added valence. The molecular structure can be fully used even after this valence is removed. However, next time you edit the molecular structure, the application will signal a valence error if you do not again add the appropriate valence.

The element's Electrons field store the element's electronic configuration, i.e., the occupancy of each electron shell. Cranium and Synapse call denotes electron shells by the letters K through R.

The element's Atomic Weight field stores the element's averaged atomic mass. To edit an element's atomic mass, you click the left mouse button in the field's value control. The application activates the Element's Atomic Weight edit dialog. See the documentation for the Datum-Reference Edit Dialog for additional details.

The Atomic Weight field can also be used to store non-active data values. The field displays a green triangle in the upper right corner of its datum control when additional, non-active data are available.

Topic	Description
Estimating Chemical Properties	a short video demonstrating how to estimate physical properties using either Synapse or Cranium.
Chemicals Chapter	the chemicals chapter contains numerous sections for entering and displaying data and estimates including the chemical structure section.
Elements Chapter	the elements chapter manages information about the atoms used to construct the molecular structures of chemicals and groups.
Groups Chapter	the groups chapter's main section enables you to enter molecular structure information.