The Element( descriptor, prop ) command constructs an element or isotope object, which represents an accepted property of an element or isotope. The object can be used, for example, to access the value, see GetValue, or the uncertainty in its value, see GetError.

isotope syntax: An isotope in the ScientificConstants package is specified by using one of the three forms of the isotope syntax: $\left[\mathrm{an}\,\mathrm{mn}\right]$, $X_{\mathrm{mn}}$, ${\mathrm{yyyy}}_{\mathrm{mn}}$, $\mathrm{Xmn}$, or $\mathrm{yyyymn}$, where an is the atomic number, mn is the mass number, X is the element symbol, and yyyy is the element name.  It is an error to specify a mass number less than the (given or implied) atomic number.

For a complete list of elements, see Initial Elements of the Periodic Table. To list the isotopes of an element, use the 'element' option with the GetIsotopes function.

If no options are specified, an object is returned with no system of units. When such an object is evaluated or queried, it returns the property value in the current system of units. For more information, see Units[UsingSystem].

If the 'units' option is specified and the 'system' equation is not specified, the units are selected from the current system of units.

To access the value of an object with units, use the evalf function.

The opts argument can contain one or more of the following equations that set object options.

'system' = symbol

This option controls the system of units associated with the object. If the system specified is a system of units accepted by the Units package, the returned element or isotope object has the system of units specified in index notation. For a list of accepted systems of units, see Units/Systems. When such an object is evaluated or queried, it returns the element or isotope property value in the indicated system of units.

parameterized element properties and stored procedures: An Element object can refer to an element with a property that has its value or uncertainty defined by a stored procedure.  When such an object is evaluated (by evalf, GetValue, or GetError), the value or uncertainty is obtained by evaluating the stored procedure. The result is then passed to the required units conversion.

Furthermore, any parameters to the property given in the Element object are passed as arguments to the procedure when it is evaluated.  In such a case, the property is said to be parameterized.

If the property value is defined by a procedure, then at the time of construction of the Element object, a trial evaluation of the procedure is done (and the result is discarded).  This allows any error from a procedure defining the property value to be rethrown immediately at the time of construction of the Element object.  Any error from a procedure defining the property uncertainty is rethrown when the Element object is evaluated with GetError.

If parameters are given for the property in the Element constructor and the corresponding stored value is not a procedure, an error is returned. Or, if parameters are given and the corresponding stored uncertainty is not undefined and not a procedure, an error is returned.

$\mathrm{with}\left(\mathrm{ScientificConstants}\right)$

$\left[\mathrm{AddConstant}\,\mathrm{AddElement}\,\mathrm{AddProperty}\,\mathrm{Constant}\,\mathrm{Element}\,\mathrm{GetConstant}\,\mathrm{GetConstants}\,\mathrm{GetElement}\,\mathrm{GetElements}\,\mathrm{GetError}\,\mathrm{GetIsotopes}\,\mathrm{GetProperties}\,\mathrm{GetProperty}\,\mathrm{GetUnit}\,\mathrm{GetValue}\,\mathrm{HasConstant}\,\mathrm{HasElement}\,\mathrm{HasProperty}\,\mathrm{ModifyConstant}\,\mathrm{ModifyElement}\right]$

$\mathrm{Element}\left(\mathrm{Na}\left[23\right]\,\mathrm{atomicmass}\right)$

$\mathrm{Element}\left({\mathrm{Na}}_{23}\,\mathrm{atomicmass}\right)$

$\mathrm{GetValue}\left(\right)\;$$\mathrm{GetUnit}\left(\right)$

$3.817543673\times {10}^{\mathrm{-26}}$

$⟦\mathrm{kg}⟧$

$\mathrm{Element}\left(\mathrm{Na}\left[23\right]\,\mathrm{atomicmass}\,\mathrm{units}\right)$

${\mathrm{Element}}_{\mathrm{SI}}\left({\mathrm{Na}}_{23}\,\mathrm{atomicmass}\right)⟦\mathrm{kg}⟧$

$\mathrm{evalf}\left(\right)$

$3.817543673\times {10}^{\mathrm{-26}}⟦\mathrm{kg}⟧$

$\mathrm{Element}\left(\mathrm{Na}\left[23\right]\,\mathrm{atomicmass}\,\mathrm{system}=\mathrm{CGS}\right)$

${\mathrm{Element}}_{\mathrm{CGS}}\left({\mathrm{Na}}_{23}\,\mathrm{atomicmass}\right)$

$\mathrm{GetValue}\left(\right)\;$$\mathrm{GetUnit}\left(\right)$

$3.817543673\times {10}^{\mathrm{-23}}$

$⟦g⟧$

$\mathrm{Element}\left(\left[11\,23\right]\,\mathrm{atomicmass}\right)$

$\mathrm{Element}\left({\mathrm{Na}}_{23}\,\mathrm{atomicmass}\right)$

$\mathrm{Element}\left(\mathrm{Mo}\,\mathrm{atomicweight}\right)$

$\mathrm{Element}\left(\mathrm{Mo}\,\mathrm{atomicweight}\right)$

$\mathrm{Element}\left(\mathrm{O}\,\mathrm{density}\right)$

Error, (in ScientificConstants:-Element) element is a gas, access ideal density with parameter 'gas'

$\mathrm{Element}\left(\mathrm{O}\,\mathrm{density}\left(\mathrm{gas}\right)\right)$

$\mathrm{Element}\left(\mathrm{O}\,\mathrm{density}\left(\mathrm{gas}\right)\right)$