Atomic force microscopy (AFM) image of a PTCDA molecule, in which the five six-carbon rings are visible.
Steam and liquid water are two different forms of the same chemical (pure) substance: water.
Isobutane structural formula
Molecular formula: C4H10
Condensed or semi-structural chemical formula: (CH3)3CH
A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings.
Colors of a single chemical (Nile red) in different solvents, under visible and UV light, showing how the chemical interacts dynamically with its solvent environment.
Traditional formula: MC60 The "@" notation: M@C60
AFM image of 1,5,9-trioxo-13-azatriangulene and its chemical structure.
Native sulfur crystals. Sulfur occurs naturally as elemental sulfur, in sulfide and sulfate minerals and in hydrogen sulfide.
A covalent bond forming H2 (right) where two hydrogen atoms share the two electrons
Potassium ferricyanide is a compound of potassium, iron, carbon and nitrogen; although it contains cyanide anions, it does not release them and is nontoxic.
Sodium and fluorine undergoing a redox reaction to form sodium fluoride. Sodium loses its outer electron to give it a stable electron configuration, and this electron enters the fluorine atom exothermically.
Cranberry glass, while appearing homogeneous, is a mixture consisting of glass and gold colloidal particles of about 40nm in diameter, giving it a red color.
3D (left and center) and 2D (right) representations of the terpenoid molecule atisane
Chemicals in graduated cylinders and beaker.
Structure and STM image of a "cyanostar" dendrimer molecule.
Hydrogen can be removed from individual H2TPP molecules by applying excess voltage to the tip of a scanning tunneling microscope (STM, a); this removal alters the current-voltage (I-V) curves of TPP molecules, measured using the same STM tip, from diode like (red curve in b) to resistor like (green curve). Image (c) shows a row of TPP, H2TPP and TPP molecules. While scanning image (d), excess voltage was applied to H2TPP at the black dot, which instantly removed hydrogen, as shown in the bottom part of (d) and in the rescan image (e). Such manipulations can be used in single-molecule electronics.

Chemical formulae can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than chemical names and structural formulae.

- Chemical formula

Earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties.

- Molecule

The chemical formula for a molecule uses one line of chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, and plus (+) and minus (−) signs.

- Molecule

A chemical compound can be either atoms bonded together in molecules or crystals in which atoms, molecules or ions form a crystalline lattice.

- Chemical substance

Chemists frequently refer to chemical compounds using chemical formulae or molecular structure of the compound.

- Chemical substance
Atomic force microscopy (AFM) image of a PTCDA molecule, in which the five six-carbon rings are visible.

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Chemical compound

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A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) composed of atoms from more than one element held together by chemical bonds.

A chemical formula specifies the number of atoms of each element in a compound molecule, using the standard abbreviations for the chemical elements and numerical subscripts.