The behavior of massive fractionally charged particles in matter is governed by the laws of chemistry if electromagnetic interactions dominate at atomic distances. Chemical properties of such "quark atoms" can be predicted by interpolating isoelectronic sequences. The properties of quark atoms lie between those of a neutral atom and an ion. Electronegativity helps in the qualitative understanding of quark chemistry. Electronegativities, together with ionization potentials and electron affinities, are computed for the quark elements. The concepts of chemical analogy and isomorphism are introduced. Analogies based on shell structure and electronegativity are established. Many quark elements cannot be compared to a single ordinary element. They are chemical chimeras. An understanding of quark chemistry is essential for the design and interpretation of quark-search experiments. The impact of chemical reactions on quark impurities in matter can be monitored by observing the behavior of more abundant isomorphic control elements. Contrary to common belief, the chemical differences between a quark element and its ordinary counterpart are substantial.