Science - 8

Matter - Substance (pure substance)

Matter with a fixed composition and definite properties (element or compound).

Matter - Element

Pure substance made of only one type of atom; cannot be broken down chemically.

Matter - Compound

Pure substance made of two or more elements chemically combined in a fixed ratio.

Matter - Chemical formula

A combination of element symbols and subscripts showing types and numbers of atoms in a compound.

Matter - Subscript in a formula

Small number that tells how many atoms of that element are present in one formula unit/molecule.

Matter - Mixture

Combination of substances that are not chemically bonded; composition can vary; can be separated physically.

Matter - Heterogeneous mixture

Mixture that is not evenly mixed; you can see different parts/phases.

Matter - Homogeneous mixture (solution)

Mixture evenly mixed throughout; appears uniform.

Matter - Solute

Substance dissolved in a solution (usually smaller amount).

Matter - Solvent

Substance that does the dissolving (usually larger amount).

Matter - Compound vs Solution

Compound: elements chemically bonded, fixed ratio. Solution: substances physically mixed, variable ratio.

Matter - Physical property

A characteristic observed/measured without changing a substance’s identity.

Matter - Chemical property

A characteristic describing a substance’s ability to form new substances.

Matter - Physical change

Change in form/state/size without forming a new substance.

Matter - Chemical change

Change that forms one or more new substances (new composition).

Matter - Evidence of chemical change

Possible signs: gas produced, precipitate forms, color change, odor change, energy change (heat/light).

Matter - Law of Conservation of Mass

Mass is not created or destroyed in physical or chemical changes; atoms are conserved.

Matter - Mass

Amount of matter in an object; measured with a balance.

Matter - Volume

Amount of space an object takes up.

Matter - Volume of a rectangular solid

V = length × width × height (cm³).

Matter - Volume by water displacement

Submerge object; volume = final water level − initial water level.

Matter - Density (concept)

How much mass is packed into a given volume; a characteristic property of a substance.

Matter - Density and floating

Less dense than fluid → floats; more dense → sinks.

Matter - Conductivity

Ability to transfer heat or electricity.

Matter - Solubility

How much solute can dissolve in a given amount of solvent at a given temperature.

Matter - Solubility and temperature (common pattern)

Many solids dissolve better in warmer liquids; gases usually dissolve better in colder liquids.

Matter - Melting point

Temperature at which a solid becomes a liquid.

Matter - Boiling point

Temperature at which a liquid becomes a gas throughout the liquid.

Matter - Filtration

Separation method using a filter to separate an insoluble solid from a liquid.

Matter - Distillation

Separation method using different boiling points; vaporize then condense.

Matter - Evaporation (as separation)

Let solvent evaporate to leave dissolved solute behind.

Matter - Chromatography

Separation method based on different attractions to a moving solvent and a stationary medium.

Matter - Magnetism (as separation)

Use a magnet to remove magnetic materials from a mixture.

Matter - Physical property: viscosity

Resistance of a liquid to flow (thicker = higher viscosity).

Matter - Physical property: luster

How a surface reflects light (shiny vs dull).

Matter - Physical property: malleability

Ability to be hammered into sheets.

Matter - Physical property: ductility

Ability to be drawn into wire.

Matter - Intensive vs extensive property

Intensive does not depend on amount (density, melting point). Extensive depends on amount (mass, volume).

States of Matter - Kinetic Molecular Theory (KMT)

Matter is made of particles in constant motion; particle speed increases with temperature.

States of Matter - Particle motion in solids

Particles vibrate in fixed positions; strong attractions.

States of Matter - Particle motion in liquids

Particles slide past each other; moderate attractions; fixed volume, variable shape.

States of Matter - Particle motion in gases

Particles move freely, far apart; weak attractions; no fixed shape or volume.

States of Matter - Plasma

High-energy state of matter made of charged particles (ions and electrons).

States of Matter - Thermal energy

Total energy of all particles in a substance (kinetic + potential).

States of Matter - Kinetic energy (particles)

Energy of motion; higher temperature usually means higher average kinetic energy.

States of Matter - Potential energy (particles)

Stored energy from particle attractions/spacing; changes during state changes.

States of Matter - Temperature

Measure of average kinetic energy of particles.

States of Matter - Endothermic state change

Absorbs energy: melting, vaporization/boiling, evaporation, sublimation.

States of Matter - Exothermic state change

Releases energy: freezing, condensation, deposition.

States of Matter - Melting

Solid → liquid; particles gain energy, move more, attractions weaken.

States of Matter - Freezing

Liquid → solid; particles lose energy, move less, attractions strengthen.

States of Matter - Vaporization

Liquid → gas (includes boiling and evaporation).

States of Matter - Boiling vs Evaporation

Boiling: throughout liquid at boiling point. Evaporation: at surface, can happen below boiling point.

States of Matter - Condensation

Gas → liquid; particles lose energy; forms droplets.

States of Matter - Sublimation

Solid → gas without becoming liquid.

States of Matter - Deposition

Gas → solid without becoming liquid.

States of Matter - Gas pressure

Force per area from gas particles colliding with surfaces.

States of Matter - Boyle’s Law

At constant temperature, gas pressure and volume are inversely related (P↑ when V↓).

States of Matter - Boyle’s Law example

If volume is cut in half (T constant), pressure doubles.

States of Matter - Charles’s Law

At constant pressure, gas volume is directly related to temperature (V↑ when T↑).

States of Matter - Absolute zero

0 K; theoretical point where particle motion is minimal.

States of Matter - Kelvin conversion

K = °C + 273 (approx).

States of Matter - Surface tension

Attraction between liquid particles at the surface causing the surface to act like a skin.

States of Matter - Cohesion

Attraction between molecules of the same substance (water-water).

States of Matter - Adhesion

Attraction between molecules of different substances (water-glass).

States of Matter - Vapor

Gas form of a substance that is normally a liquid or solid at room temperature (water vapor).

States of Matter - Crystalline solid

Particles in a repeating, orderly pattern (crystals).

States of Matter - Amorphous solid

No repeating crystal structure (glass, many plastics).

Atom - Atom

Smallest unit of an element that still has that element’s properties.

Atom - Nucleus

Dense center of the atom containing protons and neutrons.

Atom - Proton

Positively charged particle in the nucleus; mass about 1 amu.

Atom - Neutron

Neutral particle in nucleus; mass about 1 amu.

Atom - Electron

Negatively charged particle in electron cloud; tiny mass compared to proton/neutron.

Atom - Charge rules

Opposite charges attract; like charges repel.

Atom - Atomic number

Number of protons in the nucleus; identifies the element.

Atom - Mass number

Protons + neutrons in the nucleus.

Atom - Isotope

Atoms of the same element with different numbers of neutrons.

Atom - Average atomic mass

Weighted average of isotopes based on natural abundance (on periodic table).

Atom - Ion

Atom that has gained or lost electrons, giving it a net charge.

Atom - Cation

Positive ion formed by losing electrons.

Atom - Anion

Negative ion formed by gaining electrons.

Atom - Finding neutrons

Neutrons = mass number − atomic number.

Atom - Neutral atom electron count

In a neutral atom, number of electrons = number of protons.

Atom - Democritus

Proposed matter is made of tiny particles called atoms (idea, not tested).

Atom - Dalton Atomic Theory (core ideas)

Matter made of atoms; atoms of an element are identical; atoms combine in whole-number ratios; reactions rearrange atoms.

Atom - Cathode ray tube experiment

Showed rays were made of negatively charged particles (electrons).

Atom - J.J. Thomson model

Plum pudding model: electrons embedded in positive matter.

Atom - Rutherford gold foil experiment

Most alpha particles passed through; some deflected strongly.

Atom - Rutherford conclusion

Atom is mostly empty space with a small, dense, positively charged nucleus.

Atom - Proton discovery (idea)

Positive charge concentrated in nucleus; later identified as protons.

Atom - Chadwick

Discovered the neutron, explaining extra mass in nucleus.

Atom - Bohr model

Electrons orbit nucleus in specific energy levels; explains line spectra for hydrogen.

Atom - Electron cloud model

Electrons are found in regions of probability (orbitals), not fixed paths.

Atom - Energy level

Region around nucleus where an electron is likely to be found with a certain energy.

Atom - Valence electrons (definition)

Electrons in the outermost energy level; involved in bonding.

Atom - Quarks

Smaller particles that make up protons and neutrons.

Atom - Scanning tunneling microscope (STM)

Device that can produce images of individual atoms on surfaces.

Atom - Radioactivity

Spontaneous emission of radiation from unstable nuclei.

Atom - Nuclear decay

Process where an unstable nucleus changes to become more stable, releasing particles/energy.

Atom - Alpha particle

2 protons + 2 neutrons; positive; low penetration.