In chemistry the numbers of atoms, molecules, or formula units, amount of substance, in a sample is reported in the SI unit “mole” (abbreviated mol). By definition 1 mole of something contains the same number of objects as there are atoms in exactly 12 g of carbon-12. This number (i.e., 6.0221 x 10^23) is known as Avogadro's constant.

A chemical substance may consist of atoms of a single element (e.g., O2), or of different elements (e.g., CO2). The molar mass of an element is the mass per mole of its atoms. The molar mass of a compound is the mass per mole of its molecules. The molar mass of an ionic compound is mass per mole of its formula units. To calculate the molar mass of a substance we add up the individual molar masses of the constituent atoms.

Note: In nature a sample of an element contains isotopes. Isotopes are atoms with the same number of protons in the nucleus (atomic number), but different masses. The difference in mass between isotopes is the result of different numbers of neutrons. The value of the molar mass of an element used in chemical calculations takes the natural abundance of isotopes into account (i.e., the molar mass is the weighted sum of the isotopic masses found in a typical sample).

To use this calculator enter a chemical formula and tap OK, or alternatively, select a sample molecule from the menu. For example, if you needed the molar mass of sulfuric acid you would enter H2SO4. Parentheses can also be used: the formula for pentane could be entered as CH3(CH2)3CH3 or CH3CH2CH2CH2CH3.

Atoms and ions are brought to life in "Salts" -- a fully interactive atomistic simulation that reveals the motions of atoms and ions as they interact to form beautiful crystals. Discover the physics behind the structures and properties of these minerals, and explore the effects of charge and ionic radii on melting points, bond strength, and crystal lattices.

Fun for all ages! In this App you can interact with a sophisticated computational chemistry simulation right on your iPad. This 2-D Molecular Dynamics simulation computes the motions of atoms and ions as they attract or repel, and collide with one another. Modeled after the user interactions from "Atoms in Motion": with the tap of a finger you can add, delete, and move atoms, pinch or expand to dynamically change the volume, and with a gentle swipe of your finger the temperature can be scaled between 1 - 1,500K. Now as you build and create experiments, you can easily save, manage, and organize them from within the App.

Learn about Coulomb's law, the states-of-matter, and the behaviors of ionic solids, liquids, and gases! This Molecular Dynamics simulation solves the pairwise Coulombic interactions between ions and includes a strong repulsive shell to define their radius. "Salts" includes the following ions: Na+, Cl-, Ca2+, and S2-; and a neutral gas atom: He. In the simulation you can readily make NaCl (Sodium Chloride) and CaS (Calcium Sulfide) crystals -- both of which have the rock salt structure. Alternatively, you can create more complex salts such as CaCl2 (Calcium Chloride) and Na2S (Sodium Sulfide) to explore the effects of balancing charges within the crystals. Finally, the simulation includes helium (He), which is a neutral noble gas element that interacts through van der Waals forces.

Enjoy the atoms (and the ions)!

ChemiCalc is a powerful unit converter for chemistry and physics calculations. Students and teachers can enter and simultaneously view converted values for energy, wavelength and frequency. Formulas and fundamental constants relevant for quantum mechanics are included.

Chemical reactions don’t just happen—you have to make them happen. ChemCrafter lets you build your own lab to run fun and creative experiments. Use the Chem-o-convertor to measure energy released and gain points that unlock new experiments, equipment, and chemicals. Use your new supplies to craft more gases, liquids, and solids.

As your strategy guides you through experiments with water, acids, and salts, you’ll create surprising color changes, encounter fire and smoke, release various gases, and shatter equipment as your achievements earn you an impressive set of trophy-room badges.