Chemistry
An atom is a nested structure: a nucleus (dense enclosure of protons and neutrons) surrounded by electron shells (outer enclosures). The whole thing is a pattern of enclosures within enclosures.
The periodic table — that iconic chart of all elements — is a map of pattern complexity. Hydrogen is the simplest: one proton, one electron. As you move across the table, the patterns become more complex: more marks, deeper nesting, more juxtaposed elements.
When two atoms bond, they're not "sticking together." They're sharing an enclosure:
In covalent bonds, atoms share electrons — the marks that define the outer boundary. In ionic bonds, one atom transfers a mark to another — one enclosure loses a mark, the other gains one. In metallic bonds, marks are free to move across a sea of enclosures.
Every bond type is a different way of arranging marks and enclosures.
A chemical reaction is Calling and Crossing applied to molecular patterns:
The conservation of mass is a pattern principle: you can't create or destroy marks, only rearrange them. The energy released or absorbed is the "cost" of reorganizing the pattern — breaking old enclosures and forming new ones.
Every molecule is a sentence in the language of marks and enclosures. Every reaction is a rewrite according to Calling and Crossing. The periodic table is the alphabet. Stoichiometry is counting marks. Organic chemistry is complex nesting. Biochemistry is pattern systems that maintain themselves.