Short answers, pulled from the story.
Chemistry is the scientific study of the properties and behavior of matter, including its composition, structure, and the changes it undergoes during reactions. It is called the central science because it occupies an intermediate position between physics and biology and provides a foundation for understanding both basic and applied scientific disciplines.
The word chemistry comes from a Renaissance modification of the word alchemy, an earlier set of practices that mixed metallurgy, philosophy, astrology, astronomy, mysticism, and medicine. Alchemy traces through the Arabic al-kimiya to the Ancient Greek and possibly to Kemet, the ancient name of Egypt.
An atom is the basic unit of chemistry, with a nucleus of protons and neutrons surrounded by an electron cloud. A chemical element is a pure substance made of a single type of atom defined by its number of protons, while a compound is a pure substance composed of more than one element.
Chemistry became an established science through Antoine Lavoisier, who developed a law of conservation of mass that demanded careful measurement and quantitative observation. The crucial difference from alchemy was the scientific method that chemists employed, replacing alchemy's non-scientific approach.
The chemical bond can be a covalent bond, an ionic bond, a hydrogen bond, or a result of Van der Waals force. An ionic bond forms when a metal loses electrons to a non-metal, as in sodium chloride, while a covalent bond involves two atoms sharing pairs of valence electrons.
Chemistry is typically divided into analytical chemistry, biochemistry, inorganic chemistry, materials chemistry, organic chemistry, physical chemistry, and theoretical chemistry. It also generates interdisciplinary fields such as astrochemistry, geochemistry, green chemistry, and medicinal chemistry.