Science / Chemistry Glossary

Mole: SI unit for amount of substance, defined as the number of atoms in exactly 12 g of carbon-12. One mole of a molecular compound contains Avogadro's number molecules and has a mass equal to th . . . View Full Definition

Mole Fraction: Concentration of a substance in a mixture measured as moles of the substance per mole of mixture. For example, the mole fraction of oxygen in air is about 0.21, which means that 1 mol of air . . . View Full Definition

Molecular Equation: A molecular equation is a balanced chemical equation in which ionic compounds are written as neutral formulas rather than as ions. For example, agno3(aq) + nacl(aq) = agcl(s) + nano3(aq) is . . . View Full Definition

Molecular Formula: A notation that indicates the type and number of atoms in a molecule. The molecular formula of glucose is C6H12O6, which indicates that a molecule of glucose contains 6 atoms of carbon, 12 a . . . View Full Definition

Molecular Geometry: 1. The three-dimensional shape of a molecule. For example, methane (CH4) has a tetrahedral molecular geometry. 2. The study of molecular shapes.

Molecular Model: A representation of a molecule. The model can be purely computational or it can be an actual physical object. Stick models show bonds, ball-and-stick models show bonds and atoms, and spacefi . . . View Full Definition

Molecular Orbital: A wavefunction that describes the behavior of an electron in a molecule. Molecular orbitals are usually spread across many atoms in the molecule, and they are often described as a combinatio . . . View Full Definition

Molecular Sieve: A material that contains many small cavities interconnected with pores of precisely uniform size. Zeolites are an example. Molecular sieves adsorb molecules that are small enough to pass thr . . . View Full Definition

Molecular Weight: The average mass of a molecule, calculated by summing the atomic weights of atoms in the molecular formula. Note that the words mass and weight are often used interchangeably in chemistry.

Molecule: The smallest particle of an element or compound that retains the chemical properties of the element or compound. A molecule is a collection of chemically bound atoms with characteristic comp . . . View Full Definition

Momentum: Momentum is a property that measures the tendency of a moving object to keep moving in the same direction. Increasing the speed of an object increases its momentum, and a heavy object will h . . . View Full Definition

Monochromatic: Radiation that has a single wavelength.

Monodentate: A ligand that has only one atom that coordinates directly to the central atom in a complex. For example, ammonia and chloride ion are monodentate ligands of copper in the complexes [Cu(NH3)6 . . . View Full Definition

Monomer: A small molecule that is linked with large numbers of other small molecules to form a chain or a network (polymer).

Monosaccharide: A carbohydrate that cannot be decomposed into simpler carbohydrates by hydrolysis.

Mother Liquor: The solution in recrystallization.

Msds: Safety information sheet for a particular substance that lists physical properties, hazards, cleanup and disposal procedures, fire and explosion data, and protective equipment required.

Msg: MSG is monosodium glutamate, used as a flavor enhancer in many foods.

Multiple Bond: Sharing of more than one electron pair between bonded atoms. A double bond consists of two shared pairs of electrons; a triple bond consists of three shared pairs.

Nano: Prefix used in the SI system meaning 'multiply by 10-9'. For example 1 nm means '0.000000001 m'; 2.8 ng could also be written '2.8 × 10-9 g'.

Nanometer: A unit of length, equal to 10-9 meters, and equal to 10 Å (Angstroms).

Native: Naturally occuring forms of precious metals, for example, native copper, native gold, and native silver. Native metals are often very impure.

Natural Abundance: The average fraction of atoms of a given isotope of an element on Earth.

Natural Gas: A mixture of methane and other gases, found trapped over petroleum deposits under the earth.

Needle Valve: A valve which allows fine control over the rate of gas or liquid flowing through it. The valve contains a thin needle with a point that fits into a conical cup. When the valve is closed, the . . . View Full Definition

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