= Chemical bond
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A <chemical bond> associates <chemical atoms> or groups of <chemical atoms> into a sufficiently stable structure to treat it as a distinct entity. The concept covers connections within <molecules> and in extended solids; see the https://goldbook.iupac.org/terms/view/CT07009[IUPAC Gold Book, chemical bond]. It is useful because composition alone does not specify how the <chemical atoms> are connected, and those connections help determine a <chemical substance>'s properties and possible <chemical reactions>.
In a <covalent bond>, <Electrons> are shared between <chemical atoms>. Two <hydrogen> <chemical atoms> can form a <molecular hydrogen> <molecule>, with its <Electrons> interacting with both <atomic nuclei>. In the usual description of this diatomic <molecule>, the <potential energy> as a function of nuclear separation has a minimum: moving the nuclei too close or too far raises the <energy>. See <Chemistry 2e by Paul Flowers and others/7.2 Covalent Bonding>.
Separating bonded <chemical atoms> requires <energy>; forming the corresponding <chemical bonds> releases <energy>. Whether an overall <chemical reaction> releases <energy> depends on both the <chemical bonds> broken and those formed. The lines in the <stoichiometry> diagram indicate connections schematically, rather than literal rods or a sequence of microscopic events.
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