**Foundations of Chemistry**:
– Etymology: Chemistry originates from alchemy practices, derived from the Arabic word al-kīmīā, which may have Egyptian origins.
– Evolution: Chemistry evolved from alchemy during the Renaissance.
– Modern Principles: Chemistry studies matter in various states, involves rearrangement of electrons in chemical reactions, is based on the quantum mechanical model, and considers energy and entropy crucial. Chemists use tools like spectroscopy and chromatography.
**Basic Concepts of Matter**:
– Matter Definition: Matter is defined as having rest mass and volume, can be pure substances or mixtures, and is composed of particles with rest mass.
– Atoms: Atoms are the basic units of chemistry, consisting of an atomic nucleus with protons and neutrons, balanced by electrons. Atoms retain the chemical properties of the element and are the smallest entities with chemical properties.
– Compound: Compounds are pure chemical substances with more than one element, whose properties differ from its elements. Compounds are named following IUPAC guidelines, and each has a CAS registry number for identification.
**Atomic and Molecular Structure**:
– Atom: Atoms consist of an atomic nucleus and electron cloud, with protons and neutrons in the nucleus balanced by electrons. Atoms retain the chemical properties of the element.
– Molecule: Molecules are the smallest indivisible portions of pure chemical substances, composed of atoms bound by covalent bonds. They are electrically neutral structures with paired valence electrons, and molecular ions exist when a molecule carries a charge.
**Chemical Elements and Compounds**:
– Chemical Elements: Inert gases consist of lone atoms, while other elements form molecules or atom networks. Identifiable molecules include water, air, and organic compounds. Solid Earth substances lack identifiable molecules, and ionic compounds and network solids lack molecules.
– Molecular Structure: Molecule geometry is crucial for the chemical nature, determining properties, reactivity, and stability. Diatomic, triatomic, and polyatomic molecules have varying complexities.
**Quantitative Concepts in Chemistry**:
– Substance and Mixture: Chemical substances have definite composition and properties, while mixtures are collections of substances. Examples include air and alloys, with components retaining their properties and being separable by physical means.
– Mole and Amount of Substance: The mole is a unit for the amount of substance, defined by Avogadro’s number. Molar mass is the mass of one mole of a substance, used to relate mass and the number of particles, and important in chemical reactions.
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during reactions with other substances. Chemistry also addresses the nature of chemical bonds in chemical compounds.
In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant growth (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the properties of the soil on the Moon (cosmochemistry), how medications work (pharmacology), and how to collect DNA evidence at a crime scene (forensics).
Chemistry has existed under various names since ancient times. It has evolved, and now chemistry encompasses various areas of specialisation, or subdisciplines, that continue to increase in number and interrelate to create further interdisciplinary fields of study. The applications of various fields of chemistry are used frequently for economic purposes in the chemical industry.