All Chemistry 1010 Terms

Matter

Anything that has mass and occupies space.

Non-matter

Things that do not have mass and occupy space as matter does, such as energy, light, and electromagnetic radiation.

Pure substance

Matter with a fixed, uniform chemical composition. Pure substances are either elements or compounds.

Mixture

A physical combination of two or more substances in which each substance retains its chemical identity. The composition can vary.

Element

A pure substance made of only one type of atom and cannot be broken down into simpler substances by ordinary chemical reactions.

Compound

A pure substance made of two or more different elements chemically bonded together in a fixed ratio.

Homogeneous mixture / Uniform mixture

A mixture with uniform composition throughout, meaning different portions of the mixture have the same composition. A uniform mixture is another way of describing a homogeneous mixture.

Heterogeneous mixture / Non-uniform mixture

A mixture whose composition is not uniform throughout, meaning different regions can have different compositions. A non-uniform mixture is another way of describing a heterogeneous mixture.

Chemically homogeneous

Having the same chemical composition throughout the entire sample.

Chemically heterogeneous

Having different chemical compositions in different parts of the sample.

Physically homogeneous

Having the same physical properties or physical phase throughout the sample.

Physically heterogeneous

Having different physical regions or phases within the sample, even if the chemical substances present may be similar.

Particle

A general term for a very small unit of matter, such as an atom, molecule, ion, proton, neutron, or electron.

Atom

The smallest unit of an element that still retains the chemical identity of that element.

Molecule

Two or more atoms chemically bonded together as a discrete unit.

Chemical composition

The identities and relative amounts of the elements or substances that make up a material.

Substance

Matter with a definite chemical composition and characteristic properties.

A colloid

A mixture containing very small particles dispersed throughout another substance. The particles are larger than those in a true solution but usually do not settle out.

States/phases of matter

A state of matter describes the general physical form of matter, such as solid, liquid, or gas. A liquid has a definite volume but takes the shape of its container, while a gas has neither a definite shape nor a definite volume. A physical phase is a region of matter with uniform physical and chemical properties. State and phase are not exactly the same thing. For example, oil and water can form two separate liquid phases even though both have the same state of matter: liquid. A sample can contain one or multiple phases. A phase diagram shows which phase of a substance is stable at different temperatures and pressures.

Solids

A solid has a definite shape and volume because its particles are held relatively fixed in position. A crystalline solid has particles arranged in an ordered, repeating structure called a crystal, while an amorphous solid lacks long-range repeating order.

Intermolecular forces (IMFs)

Attractive forces between separate molecules or particles. They affect properties such as boiling point, melting point, vapor pressure, and solubility.

Irreducible composition

A material whose chemical composition cannot be separated into simpler components by physical methods. Its composition is inherent to the substance.

Separation of mixtures

The process of separating components of a mixture using differences in physical properties rather than changing their chemical identities. Physical separation includes methods such as filtration or evaporation. Distillation separates substances mainly by differences in boiling points.

Chemical reaction

A process in which atoms are rearranged and substances are converted into different substances through the breaking and/or formation of chemical bonds.

Reactant

A starting substance that is consumed or changed during a chemical reaction.

Product

A substance formed by a chemical reaction.

Reagent

A chemical substance used to cause, test for, or participate in a chemical reaction. A reagent may also be a reactant.

Chemical change

A change that produces one or more substances with different chemical compositions or chemical properties.

Chemical bonding / Bonding

The attractive interactions that hold atoms together in compounds or molecules.

Attractive force

A force that pulls particles toward each other, such as attraction between opposite electric charges.

Repulsive force

A force that pushes particles apart, such as the repulsion between particles with the same electric charge.

Law of Conservation of Mass

In an ordinary chemical reaction, matter is not created or destroyed. The total mass of the reactants equals the total mass of the products.

Law of Definite Proportions (Law of Constant Composition)

A particular pure compound always contains the same elements in the same fixed proportions by mass.

Law of Multiple Proportions

When two elements form more than one compound, the different masses of one element that combine with a fixed mass of the other occur in small whole-number ratios.

Mass ratio

A comparison of the masses of two substances or elements, usually written as one mass divided by another.

Whole-number ratio

A ratio that can be expressed using small whole numbers. In chemistry, these ratios often reveal relationships between atoms or formulas of compounds.

Dalton’s atomic theory

Dalton's model proposed that matter consists of atoms, atoms of different elements differ from one another, compounds form from atoms in whole-number ratios, and chemical reactions rearrange atoms rather than create or destroy them.

Atomic theory

The general scientific theory that matter is composed of atoms and that the behavior and arrangement of atoms explain chemical properties and reactions.

Scientific method

A general process for investigating questions using observations, hypotheses, experiments, analysis, and conclusions. It is not necessarily a rigid sequence of steps.

Observation

Information obtained by measuring or examining something using the senses or scientific instruments.

Hypothesis / Scientific hypothesis

A proposed explanation for an observation that can be tested and could potentially be shown to be incorrect.

Testable

Capable of being investigated using observations or experiments that can produce evidence.

Falsifiable

Capable, in principle, of being shown to be wrong by evidence.

Experiment

A controlled procedure designed to gather evidence, test a hypothesis, or investigate a relationship.

Scientific fact

An observation or result that has been repeatedly confirmed by reliable evidence.

Scientific law

A concise description of a consistently observed relationship in nature. A law describes what happens, often mathematically, rather than necessarily explaining why.

Theory / Scientific theory

A broad, well-supported explanation of natural phenomena based on extensive evidence and repeated testing.

Scientific model

A simplified representation of a real system used to describe, explain, or predict its behavior.

Solution

A homogeneous mixture in which one or more solutes are uniformly dispersed in a solvent.

Solvent

The component of a solution that dissolves the solute and is typically present in the greatest amount.

Solute

A substance dissolved in a solvent.

Concentration

A measure of how much solute is present relative to a given amount of solution or solvent.

Molarity (M)

A concentration unit equal to moles of solute per liter of solution. M = mol solute / L solution.

Stock solution

A solution of known concentration that is used to prepare other solutions, usually by dilution.

Stock concentrate

A relatively concentrated solution intended to be diluted before use.

Sample

A portion of material or solution selected for measurement, testing, or analysis.

Solubility / Molar solubility

Solubility is the maximum amount of a solute that can dissolve in a particular amount of solvent under specified conditions, especially temperature. Solubility can be expressed using several concentration units. Molar solubility specifically expresses the maximum amount that dissolves as moles of solute per liter of solution, usually in mol/L.

Saturated

A solution containing the maximum amount of dissolved solute possible at a particular temperature and conditions. Dissolved and undissolved solute are at equilibrium if excess solid is present.

Solubility product (Ksp)

The equilibrium constant describing the dissolution of a sparingly soluble ionic compound.

Soluble

Able to dissolve to a significant extent in a particular solvent.

Insoluble

Dissolves only to a very small extent in a particular solvent. In chemistry, insoluble usually does not mean that literally zero dissolves.

Solution product (Q)

The product of the relevant ion concentrations at the current moment, calculated in the same form as Ksp. Comparing Q with Ksp predicts whether precipitation or additional dissolution will occur.

Unsaturated

A solution containing less dissolved solute than its maximum possible amount, so additional solute can dissolve.

Supersaturated

A solution containing more dissolved solute than would normally be stable at equilibrium. It is unstable and excess solute can crystallize out.

Dilution

The process of decreasing a solution's concentration by adding solvent without changing the amount of solute present. For a simple dilution in which the amount of solute stays constant, C₁V₁ = C₂V₂. A serial dilution performs several dilutions in sequence. The stock concentration is the concentration of the original solution, while the current-step concentration Cₙ is the concentration after a particular dilution step. The dilution factor Df tells how much the solution has been diluted. Df = total volume / transferred volume. For a serial dilution, Cₙ = Cₙ₋₁ / Df.

Light

Electromagnetic radiation that behaves as both a wave and a stream of particles called photons.

Electromagnetic radiation

Energy that travels through space as oscillating electric and magnetic fields. Examples include radio waves, visible light, ultraviolet light, and X-rays.

Radiation

Energy transmitted through space or matter in the form of waves or particles. Electromagnetic radiation is one type.

Electromagnetic

Describes phenomena involving interacting electric and magnetic fields.

Wave-particle duality

The principle that light and other quantum objects can display both wave-like and particle-like behavior depending on how they are observed.

Bright

Describes light with relatively high intensity. For otherwise comparable light, greater intensity corresponds to more energy arriving per unit area and time.

Dim

Describes light with relatively low intensity.

Electronic composition

The electric component of electromagnetic radiation is the oscillating electric field that travels as part of an electromagnetic wave.

Magnetic composition

The magnetic component of electromagnetic radiation is the oscillating magnetic field that travels perpendicular to the electric field and direction of motion.

Wave

A traveling disturbance that transfers energy. A wave has crests at its highest points and troughs at its lowest points. Amplitude is the vertical distance from the equilibrium position to a crest or trough. High amplitude corresponds to greater intensity, while low amplitude corresponds to lower intensity. For electromagnetic waves such as light, intensity is proportional to the square of the wave's amplitude, not directly proportional to amplitude. Wavelength is the distance between equivalent points on consecutive waves, such as the distance between two crests.

Beer-Lambert law

Relates the amount of light absorbed by a solution to the solution's concentration using A = εbc, where A is absorbance, ε is molar absorptivity, b is path length through the sample, and c is concentration. Under conditions where Beer-Lambert behavior is valid, absorbance increases linearly with concentration.

Spectrophotometry

A method that uses a spectrophotometer to measure how much light a sample absorbs. I₀ is the intensity of the incident light entering the sample, while I is the intensity of the transmitted light leaving the sample. Transmittance is T = I/I₀. Absorbance is related to transmittance by A = −log₁₀(T). A spectrophotometer can produce a curve of absorbance versus wavelength. The wavelength giving maximum absorbance, or peak maximum (λmax), is often used for measurements. For many dye solutions, greater concentration produces stronger color intensity and greater absorbance.

Grams per liter (g/L)

A concentration unit representing the number of grams of solute present per liter of solution.

Subatomic level

The scale involving particles smaller than an atom, such as electrons, protons, and neutrons, and the internal structure of atoms.

Cathode-ray tube / Discovery of the electron

A cathode-ray tube produces a beam called a cathode ray. J. J. Thomson showed that the beam was deflected by electric and magnetic fields, demonstrating that it consisted of negatively charged particles later called electrons. His experiments measured the electron's charge-to-mass ratio. The modern accepted value is approximately −1.76 × 10⁸ C/g. These experiments provided evidence that atoms contain smaller subatomic particles.

Electron

A negatively charged subatomic particle found outside the nucleus of an atom. Its charge is one negative elementary charge, approximately −1.60 × 10⁻¹⁹ C, and its mass is approximately 9.11 × 10⁻²⁸ g. The elementary charge is the fundamental magnitude of electric charge carried by a proton or electron, with the electron carrying −e.

Oil-drop experiment

Millikan's experiment used an oil-drop apparatus in which electrically charged oil droplets were balanced using an electric field. The modern accepted magnitude of the electron's charge is approximately 1.60 × 10⁻¹⁹ C. The experiment also demonstrated quantization of charge, meaning observed electric charges occur in whole-number multiples of the elementary charge.

Electric charge

A property of particles that causes electric attraction or repulsion. Charge may be positive or negative and is measured in coulombs (C), the SI unit of electric charge.

Alpha-particle experiments

Rutherford's scattering experiments fired positively charged alpha particles at thin metal foil. Most passed through, showing that atoms are mostly empty space, while a small number were strongly deflected, revealing a tiny, dense, positively charged nucleus. These observations led to the nuclear theory of the atom, in which nearly all positive charge and most atomic mass are concentrated in the nucleus.

Proton

A positively charged subatomic particle located in the nucleus. The number of protons determines the identity of an element.

Neutron

An electrically neutral subatomic particle found in the nucleus. Neutrons contribute to atomic mass and distinguish isotopes of the same element.

Atomic number (Z)

The number of protons in the nucleus of an atom. It uniquely identifies the element.

Mass number (A)

The total number of protons plus neutrons in the nucleus of a particular atom. A = Z + N. Because it counts particles, mass number is always a whole number. It is different from atomic mass measured in amu.

Neutron number (N)

The number of neutrons in an atom. N = A − Z.

Ion

An atom or group of atoms with a net electric charge because the number of electrons does not equal the number of protons.

Ion formation

The process by which a neutral atom or molecule gains or loses electrons and becomes charged. The nucleus normally does not change during ordinary ion formation.

Cation

A positively charged ion, usually formed when an atom loses one or more electrons.

Anion

A negatively charged ion, usually formed when an atom gains one or more electrons.

Atomic mass

The measured mass of an individual atom, normally expressed in atomic mass units (amu). One atomic mass unit is defined as exactly 1/12 of the mass of a carbon-12 atom. Atomic mass is different from mass number. Mass number is a whole-number count of protons plus neutrons, whereas atomic mass is a measured real value and is generally not a whole number because nuclear binding energy causes the actual mass to differ slightly from the simple sum of the particle masses. Carbon-12 is the special reference isotope whose atomic mass is defined as exactly 12 amu.

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons, giving them different mass numbers. Isotopic abundance is the fraction or percentage of each isotope found naturally. An element's average atomic mass is a weighted average based on the masses and relative abundances of its naturally occurring isotopes.

Periodic table

An arrangement of elements that reveals repeating periodic patterns in chemical and physical properties. Elements are represented by an element symbol, such as C for carbon, and are arranged primarily by atomic number. The f block contains the lanthanide and actinide series. IUPAC, the International Union of Pure and Applied Chemistry, establishes internationally accepted chemical names, symbols, terminology, and standards.

Radioactive

Describes an unstable atomic nucleus that spontaneously undergoes nuclear change and emits radiation.

Trace element

An element present in only a very small amount in a sample, substance, organism, or environment.

Mole (mol)

The SI unit for amount of substance. One mole contains exactly 6.02214076 × 10²³ specified particles, a value called Avogadro's number. Molar mass is the mass of one mole of a substance, usually expressed in grams per mole (g/mol). A gram (g) is a unit of mass, and molar mass provides the conversion between grams of a substance and moles of that substance.

Mass

A measure of the amount of matter in an object. Unlike weight, mass does not depend on the local gravitational field.