Appearance of real linear polymer chains as recorded using an atomic force microscope on a surface, under liquid medium. Chain contour length for this polymer is ~204 nm; thickness is ~0.4 nm.
Steam and liquid water are two different forms of the same chemical (pure) substance: water.
Cartoon schematic of polymer molecules
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.
Structure of a styrene-butadiene chain, from a molecular simulation.
Native sulfur crystals. Sulfur occurs naturally as elemental sulfur, in sulfide and sulfate minerals and in hydrogen sulfide.
Some memorable milestones in the history of polymers
Potassium ferricyanide is a compound of potassium, iron, carbon and nitrogen; although it contains cyanide anions, it does not release them and is nontoxic.
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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.
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Chemicals in graduated cylinders and beaker.
Microstructure of part of a DNA double helix biopolymer
Branch point in a polymer
A polyethylene sample that has necked under tension.
Thermal transitions in (A) amorphous and (B) semicrystalline polymers, represented as traces from differential scanning calorimetry. As the temperature increases, both amorphous and semicrystalline polymers go through the glass transition (Tg). Amorphous polymers (A) do not exhibit other phase transitions, though semicrystalline polymers (B) undergo crystallization and melting (at temperatures Tc and Tm, respectively).
Phase diagram of the typical mixing behavior of weakly interacting polymer solutions, showing spinodal curves and binodal coexistence curves.
A plastic item with thirty years of exposure to heat and cold, brake fluid, and sunlight. Notice the discoloration, swelling, and crazing of the material
Chlorine attack of acetal resin plumbing joint
Ozone-induced cracking in natural rubber tubing

is a substance or material consisting of very large molecules, or macromolecules, composed of many repeating subunits.

- Polymer

Polymers almost always appear as mixtures of molecules of multiple molar masses, each of which could be considered a separate chemical substance.

- Chemical substance
Appearance of real linear polymer chains as recorded using an atomic force microscope on a surface, under liquid medium. Chain contour length for this polymer is ~204 nm; thickness is ~0.4 nm.

1 related topic

Alpha

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

Molecule

Group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion.

Group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion.

Atomic force microscopy (AFM) image of a PTCDA molecule, in which the five six-carbon rings are visible.
A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings.
AFM image of 1,5,9-trioxo-13-azatriangulene and its chemical structure.
A covalent bond forming H2 (right) where two hydrogen atoms share the two electrons
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.
3D (left and center) and 2D (right) representations of the terpenoid molecule atisane
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.

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

Most molecules are far too small to be seen with the naked eye, although molecules of many polymers can reach macroscopic sizes, including biopolymers such as DNA.