M
Molality

The number of moles of solute per kilogram of solvent. Because weights of a solute/solvent are generally fixed at all temperatures, this scale is useful for experiments where physical properties (e.g., boiling point, freezing point) are examined over a temperature range.
Cf., molarity, formality, normality, mole fraction

Molarity

The number of moles of the solute in one liter of solution. Useful where experiments use measured volumes and where temperature effects are not being studied.
Cf., formality, normality, molality, mole fraction

Mole fraction

Number of moles of one component divided by the total number of moles of all components.
Cf., molarity, formality, normality, molality

Molecular dynamics (MD)

A molecular simulation for calculating time-averaged properties of a molecular system. The model system is simulated by solving Newton’s equations of motion, including kinetic and potential energy terms. The energy terms can be obtained by using classical (force field) or quantum (Density Functional Theory) methods. System constraints (e.g., constant volume, temperature, pressure) usually correspond to a thermodynamic ensemble.
Cf., density functional theory, force field, Grand Canonical Monte Carlo simulation, Monte Carlo molecular simulation, quantum calculation

Molecular orbital method

A method of calculating the electronic structure and related properties of a finite molecular system consisting of two or more atoms by solving the Schrodinger equation to determine the electronic structure. Various methods exist to approximate the simultaneous solution of the Schrodinger equation for all electrons in the molecular system.

Molecular simulation

A set of computational methods used to calculate physical or chemical properties of a model system consisting of atoms or molecules. Computed properties can include chemical reactions, structure, spectroscopy, and transport. Many techniques exist for such simulations based on model system size and desired accuracy, from quantum methods to classical (force field) methods.
Cf., force field, quantum calculations

molecularity

the number of reacting molecules, atoms, or ions in a single-step chemical reaction. For example, a unimolecular reaction may involve radioactive decay of a single atom, or one molecule producing other molecules. A bimolecular reaction involves the collision and reaction between two molecules, atoms or ions to form other products. Cf., Transition State Theory

Molecularity

The number of reacting molecules, atoms, or ions in a single-step chemical reaction. For example, a unimolecular reaction may involve radioactive decay of a single atom, or one molecule producing other molecules. A bimolecular reaction involves the collision and reaction between two molecules, atoms or ions to form other products.
Cf., Transition State Theory

Monolayer, phyllosilicate

Between 2:1 layers of a phyllosilicate, a monolayer involves an arrangement within the interlayer of one single plane of H2O molecules around interlayer cations (= hydration shell). Although the plane is only approximate, the spacing seems to suggest a planar feature. Because the H2O molecules are in planar coordination around the cation, the spacing appears as an H2O plane or “layer”.
Cf., bilayer; bilayer, phyllosilicate

Monrepite

An obsolete term for ferrian annite.