Figure 1.
Ball-and-stick model of proline
. Source.
Isomers were quite confusing for early chemists, before atomic theory was widely accepted, and people where thinking mostly in terms of proportions of equations, related: Section "Isomers suggest that atoms exist".
Exist because double bonds don't rotate freely. Have different properties of course, unlike enantiomer.
Key exmaple: d and L amino acids. Enantiomers have identical physico-chemical properties. But their biological roles can be very different, because an enzyme might only be able to act on one of them.

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TODO definition. Appears to be isomers
Example:
Molecules that are the same if you just look at "what atom is linked to what atom", they are only different if you consider the relative spacial positions of atoms.

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Chemical bond by Wikipedia Bot 0
A chemical bond is a lasting attraction between atoms, ions, or molecules that enables the formation of chemical compounds. Chemical bonds are fundamental to the structure and properties of substances and are involved in chemical reactions. There are several main types of chemical bonds: 1. **Ionic Bonds**: Formed when one atom donates one or more electrons to another atom, leading to the formation of charged ions.