Chemistry: Types of Matter, Particulate Theory, and Changes of State

Comprehensive vocabulary flashcards covering the classification of pure substances and mixtures, the particulate theory of matter, evidence for particle behavior (diffusion, osmosis, Brownian motion), and physical changes of state.

Matter

Anything that has volume and mass, is composed of particles, and exists in solid, liquid, or gaseous states.

Pure substance

A substance composed of a single type of material with a fixed composition and constant properties (such as melting point, boiling point, and density) that cannot be separated by physical processes.

Element

A pure substance that cannot be broken down into simpler substances by any ordinary physical or chemical process, composed of atoms of one kind only.

Compound

A pure substance formed from atoms of two or more different types of elements chemically bonded together in fixed proportions in a way that alters their properties.

Mixture

A combination of two or more substances that are not chemically combined, having variable composition and properties, which can be separated by physical methods.

Homogeneous mixture

A uniform mixture possessing the same composition and properties throughout, where component parts cannot be distinguished from each other (e.g., solutions like lime juice, air, bronze).

Heterogeneous mixture

A non-uniform mixture where component parts can be distinguished from each other, though not always with the naked eye (e.g., suspensions and colloids).

Solution

A homogeneous mixture of two or more substances, typically consisting of a solute dissolved in a liquid solvent.

Solute and solvent

The solvent is the substance present in higher concentration that does the dissolving; the solute is the substance present in lower concentration that dissolves.

Aqueous solution

A solution in which water is the solvent.

Suspension

A heterogeneous mixture in which minute, visible particles of one substance are dispersed in another substance (e.g., chalk in water, oil in water, dust in air).

Colloid

A heterogeneous mixture in which minute dispersed particles are larger than those of a solution but smaller than those of a suspension (e.g., milk, clouds, smoke).

Effect of impurities on melting and boiling points

The presence of impurities in a substance usually lowers its melting point and raises its boiling point.

Particulate Theory of Matter

A theory stating that all matter is composed of particles that are in constant motion, have empty spaces between them, and exert forces of attraction on one another.

Diffusion

The net movement of particles from an area of high concentration to an area of lower concentration down a concentration gradient until they are evenly distributed.

Rate of gas diffusion ($NH_3$ vs $HCl$)

When ammonia and hydrochloric acid diffuse toward each other in a tube, a white ring of ammonium chloride ($NH_4Cl$) forms closer to the $HCl$ end because ammonia particles travel faster.

Osmosis

The net movement of water molecules through a differentially (or partially) permeable membrane from a region of higher water concentration to a region of lower water concentration.

Osmotic behavior of plant tissue

Living tissue (such as pawpaw) swells, increases in length, and becomes rigid in pure water, but shrinks, decreases in length, and becomes softer in concentrated sodium chloride solution.

Brownian motion

The random, irregular movement of microscopic particles suspended in a fluid resulting from continuous bombardment by molecules of the surrounding fluid.

Einstein's explanation of Brownian motion

In 1905, Albert Einstein modeled the erratic motion of pollen grains observed by Robert Brown (1827) as collisions with water molecules, validating the atomic hypothesis and enabling the calculation of atomic sizes.

Applications of osmosis

Practical uses include eradicating slugs and snails via dehydration, preserving food by drawing water out of bacteria and fungi, and relieving sore throats by drawing excess water from swollen throat cells using salt water gargles.

Melting

The phase change from solid to liquid occurring when particles gain kinetic energy to overcome intermolecular attractions; happens at a constant temperature called the melting point.

Evaporation

The slow vaporization of a liquid into a gas that occurs only at the liquid's surface at any temperature below the boiling point, producing a cooling effect.

Boiling

The rapid vaporization of a liquid into a gas occurring throughout the bulk of the liquid at a specific constant temperature known as the boiling point.

Sublimation

The direct transition of a substance from a solid to a gas without passing through the liquid state (e.g., dry ice, iodine, ammonium chloride, naphthalene).

Deposition

The phase change where a gas transforms directly into a solid without entering an intermediate liquid state.

Cooling curve

A plot of temperature against time as a substance is cooled, displaying horizontal plateaus at phase transitions where temperature remains constant while heat is removed.

Factors affecting the rate of evaporation

The rate of evaporation increases with increased surface area, higher temperature, and higher wind speed, and decreases with higher humidity.

Latent heat of vaporization

The heat energy absorbed from the surroundings when a liquid changes into a gas, which accounts for the cooling effect experienced during evaporation.

Conservation of mass during state changes

The total mass of a substance remains constant when changing states, even though its volume and density vary.

Temperature

A measure of the average kinetic energy of the particles within a sample of matter.

Atom, molecule, and ion

An atom is the smallest unit of an element; a molecule consists of two or more bonded atoms existing independently; an ion is an electrically charged atom or group of atoms.