Standard States of Elements
The standard states of elements are the forms that they adopt at a temperature of 25°C and pressure of 1 atmosphere (1 atm).
These forms of the elements are the reactants in the formation equations of multi- element substances.
The heat of formation (∆H°f) of an element in its standard state is zero.
Below is the list of the elements whose standard states you need to know for this course. Please note that some elements have multiple possible forms at the standard state such as carbon, which can be either graphite or diamond. However only one of these forms is the true standard state; in those cases the proper state will be listed next to the formula for the element.
• Hydrogen H2(g)
• Nitrogen N2(g)
• Oxygen O2(g)
• Fluorine F2(g)
• Chlorine Cl2(g)
• Bromine Br(l)
• Mercury Hg(l)
There are two distinct classes of elemental solids. Molecular solids, unlike other elemental solids, have specific molecular structures (arrangements of bonded atoms) that are packed close to each other (held by van der Waals forces) to form the solid. The atoms of a molecular solid are only bonded to the other atoms in their specific molecule, unlike the elements in the other elemental solids, which are bound to all their nearest neighboring elements.
Phosphorus P4 – white
Sulfur S8(s) – rhombic crystalI2(s)
Carbon C(s) – graphite
Common Ionic Species in Aqueous Solution
Below is the list of common aqueous ions that you are expected to know for this course. You need to know the name, formula, and charge of each ion as the names and formulas will be used interchangeably in homework and exam questions.
Cations (positively charged ions)
Anions (negatively charged ions)