Matter, Atoms, Molecules, Ions, Substances, Mixtures, and Energy
Matter
Matter is anything that occupies space, has mass, and is subject to measurable changes over time and interactions with measuring devices. In physics and philosophy, matter constitutes objective material reality, perceivable identically by different subjects. It includes all objects visible or detectable by physical means.
The term also refers to the subject of literary, scientific, or political works. This leads to the “matter-form” opposition, where the same content or subject can be treated in various ways: style, expression, focus, or point of view. It also denotes a subject or discipline in teaching.
Atom
In chemistry and physics, an atom (from Latin atomum, from Greek ἄτομον, “indivisible”) is the smallest unit of a chemical element retaining its identity and properties, and indivisible by chemical processes.
Its dense nucleus, containing protons and neutrons (baryons), accounts for 99.9% of the atom’s mass. A cloud of electrons surrounds the nucleus, equal in number to the protons in a neutral atom.
Ancient Greek atomists postulated atoms as indivisible building blocks of matter. However, their existence was only proven in the nineteenth century. Twentieth-century nuclear physics revealed that atoms can be further divided into smaller particles.
Molecule
In chemistry, molecules are neutral particles formed by a stable group of at least two covalently linked atoms.
Organic and much of inorganic chemistry concern the synthesis and reactivity of molecules and molecular compounds. Physical chemistry and quantum chemistry study the properties and reactivity of molecules quantitatively. Biochemistry and molecular biology study living organisms at the molecular level. Supramolecular chemistry examines specific intermolecular interactions, including molecular recognition. These forces determine physical properties like solubility and boiling point.
Molecules rarely exist without interactions, except in rarefied gases. They form crystal lattices (e.g., H2O in ice) or exhibit strong, rapidly changing interactions (e.g., liquid water). The most important intermolecular forces, in increasing intensity, are Van der Waals forces and hydrogen bonds. Molecular dynamics simulations use these forces to explain molecular properties.
Ion
An ion is an electrically charged particle formed by an atom or molecule that is not electrically neutral. This occurs when an atom or molecule gains or loses electrons, a process known as ionization.
Negatively charged ions (more electrons than protons) are anions, attracted to the anode. Positively charged ions (fewer electrons) are cations, attracted to the cathode.
Anion
An anion is an ion with a negative electric charge, having gained electrons. Anions have a negative oxidation state.
Cation
A cation is an ion (atom or molecule) with a positive electric charge, having lost electrons. Cations have a positive oxidation state.
Salts typically consist of cations and anions, although the bonding always has a covalent component. Cations, such as sodium (Na) and potassium (K), are also present in the body.
Substance
In chemistry, a substance is any portion of matter sharing certain intensive properties. The term also refers to the kind of matter forming bodies.
Substances are classified as pure substances or mixtures.
A pure substance cannot be decomposed into other substances by physical processes (heating, magnetic fields). It may decompose through chemical processes. If it can, it’s a compound; otherwise, it’s a simple substance.
A mixture results from combining pure substances and can be separated by physical (distillation, evaporation, suspension, filtration) or mechanical (decanting, magnetization) means.
A homogeneous mixture has uniform intensive properties throughout (e.g., salt dissolved in water). Intensive properties are independent of the amount of material (e.g., density, flavor, viscosity, specific heat). The Tyndall effect can determine if a mixture is homogeneous; if no particles are visible when illuminated perpendicularly, it’s homogeneous.
A heterogeneous mixture has parts with different intensive properties (e.g., sand and sawdust).
Homogeneous Mixture
Components are not visible to the naked eye or microscope. It consists of a solute and a solvent.
Colloidal Dispersion
Colloids are homogeneous mixtures with particles in the 1 to 1000 nanometer range (e.g., a particle 8 nm in diameter would be like a 40 km water drop or a 400-block structure).
Heterogeneous Mixture
A heterogeneous mixture has a non-uniform composition, with distinguishable components unevenly distributed. Components can be mechanically separated (e.g., salads, salt and earrings).
Suspension
Suspensions have fine particles temporarily suspended in a liquid, eventually settling. The initial phase shows different elements. They can be separated physically (e.g., glue (water and flour), water and oil).
Energy
The term energy (from Greek ἐνέργεια / energeia, activity, operation; ἐνεργός / energos = action, force, strength, work) has various meanings related to the capacity to act, transform, or move. In physics, energy is the ability to do work. In technology and economy, it refers to a natural resource (and its technology) for extraction, transformation, and industrial or economic use. The universal law of conservation of energy (first law of thermodynamics) states that energy in an isolated system remains constant over time. Special relativity establishes mass-energy equivalence: all bodies contain energy by virtue of their mass, and can have additional energy. Energy is conceptually divided into types based on system properties: kinetic energy (movement), chemical energy (composition), potential energy (deformation or position relative to forces), and thermal energy (thermodynamic state).