Year 8 Science: Periodic Table, Atomic Structure, and Change

Comprehensive vocabulary flashcards reviewing the classification of matter, atomic structure, periodic table trends, energy transformations, chemical versus physical changes, and geological processes.

Matter

Anything that has mass and takes up space.

Element

A pure substance made of only one type of atom that cannot be broken down into simpler substances by chemical means.

Compound

A pure substance made of two or more different elements chemically joined (bonded) in a fixed ratio, such as water ($\text{H}_2\text{O}$) or sodium chloride ($\text{NaCl}$).

Mixture

Two or more substances physically mixed together but not chemically joined, which can be separated by physical methods.

Alloy

A mixture of a metal with one or more other elements (usually metals), made to improve its properties (e.g., steel, brass, bronze).

Physical Property

A feature of a substance that can be observed or measured without changing the substance into a new substance, such as colour, melting point, or conductivity.

Lustrous

Shiny when freshly cut or polished due to reflecting light.

Malleable

Capable of being hammered or bent into a new shape without breaking.

Ductile

Capable of being stretched or drawn out into a thin wire.

Brittle

Breaks, shatters, or crumbles easily when struck or bent.

Conductor

A material that allows heat or electricity to pass through easily.

Insulator

A material that does not allow heat or electricity to pass through easily.

Metalloid (Semi-metal)

An element possessing physical and chemical properties in between those of metals and non-metals, such as silicon, boron, or germanium.

Atom

The smallest unit of an element that retains all the physical and chemical properties of that element.

Subatomic Particles

The constituent particles that compose an atom: protons, neutrons, and electrons.

Proton

A positively charged subatomic particle with a relative mass of $1$ atomic mass unit, located inside the nucleus.

Neutron

A subatomic particle with no electrical charge ($0$) and a relative mass of $1$ atomic mass unit, located inside the nucleus.

Electron

A negatively charged subatomic particle with negligible mass ($0$, or about $\frac{1}{1840}$ of a proton) orbiting the nucleus in energy levels or shells.

Atomic Nucleus

The tiny, dense centre of an atom composed of protons and neutrons (nucleons), which contains virtually all of the atom's mass.

Plum Pudding Model

J.J. Thomson's 1897 atomic model proposing that an atom consists of a diffuse sphere of positive charge containing negatively charged electrons scattered throughout.

Nuclear Model

Ernest Rutherford's 1911 atomic model, established by the gold foil experiment, showing that an atom is mostly empty space with a tiny, dense, positively charged nucleus orbited by electrons.

Planetary (Bohr) Model

Niels Bohr's 1913 atomic model in which electrons orbit the nucleus in fixed circular paths or shells at distinct energy levels.

Electron Cloud Model

Erwin Schrödinger's 1926 quantum model stating that electrons do not travel in defined orbits, but occupy regions of high probability known as electron clouds.

Periodic Table

A tabular arrangement of all known chemical elements ordered by increasing atomic number, aligning elements with similar chemical properties into columns.

Period

A horizontal row in the periodic table (7 total); all elements in the same row possess the same number of electron shells.

Group

A vertical column in the periodic table (18 total); elements within the same column have identical numbers of valence electrons and similar chemical reactivity.

Alkali Metals

Group 1 elements (excluding hydrogen) which are soft, lustrous metals that react vigorously with water to produce hydrogen gas, with reactivity increasing down the column.

Alkaline Earth Metals

Group 2 metallic elements that are reactive, though less reactive than the Group 1 alkali metals.

Transition Metals

Elements found in Groups 3 to 12 characterized by hardness, strength, high melting points, lower chemical reactivity, and the formation of colourful compounds.

Halogens

Highly reactive non-metals in Group 17 that combine with metals to form salts, with chemical reactivity decreasing down the group.

Noble Gases

Group 18 colourless, odourless, and chemically inert gases that have full outer electron shells and very low boiling points.

Flame Test

A diagnostic procedure identifying specific metal elements based on the characteristic colour of light emitted when excited electrons return to lower energy states in a flame.

Pop Test

A diagnostic test confirming hydrogen gas, where a lit splint exposed to the gas produces a distinctive squeaky 'pop' sound ($\text{hydrogen} + \text{oxygen} \rightarrow \text{water}$).

Glowing Splint Test

A diagnostic test confirming oxygen gas, where a glowing wooden splint placed into the gas relights and bursts back into flame.

Atomic Number ($Z$)

The total number of protons in the nucleus of an atom, defining the identity of a chemical element.

Mass Number ($A$)

The sum of the number of protons and neutrons in the nucleus of a single atom ($\text{protons} + \text{neutrons}$).

Isotopes

Atoms of the same chemical element that share the same number of protons but have different numbers of neutrons, resulting in different mass numbers.

Electron Configuration

The numerical arrangement of electrons distributed among energy shells moving from the innermost shell outward (e.g., sodium is $2,8,1$).

Physical Change

A change affecting the form, state, or shape of a substance without breaking or creating chemical bonds or generating a new substance; typically easy to reverse.

Chemical Change

A process where chemical bonds between atoms are broken and new bonds are formed, rearranging atoms to produce one or more new substances with different properties.

Precipitate

An insoluble solid that forms and settles out of a liquid mixture when two clear solutions chemically react, making the liquid cloudy.

Reactants

The starting substances consumed during a chemical reaction, written on the left-hand side of a word equation.

Products

The new substances generated by a chemical reaction, written on the right-hand side of a word equation.

Law of Conservation of Mass

The physical law stating that mass is neither created nor destroyed during a chemical reaction; the total mass of the reactants equals the total mass of the products.

Exothermic Reaction

A chemical reaction that releases energy (usually as heat) into the surrounding environment, resulting in a temperature increase.

Endothermic Reaction

A chemical reaction that absorbs energy from the surrounding environment, resulting in a temperature decrease.

Photosynthesis

An endothermic biological process in plant chloroplasts utilizing radiant energy from the Sun to convert carbon dioxide and water into glucose and oxygen.

Cellular Respiration

An exothermic biological process in the mitochondria of living cells that breaks down glucose in the presence of oxygen to release usable cellular energy, yielding carbon dioxide and water.

Thermal Energy

The total internal kinetic energy possessed by all the moving and vibrating particles comprising a substance.

Conduction

The transfer of thermal energy through matter via successive collisions between neighbouring particles without bulk movement of the particles themselves.

Convection

The transfer of thermal energy through fluids (liquids or gases) caused by the physical circulation of fluid currents as warmer, less dense regions rise and cooler, denser regions sink.

Thermal Radiation

The transfer of heat via electromagnetic waves (primarily infrared) that requires no physical medium and can propagate through a vacuum.

Potential Energy ($\text{PE}$)

Energy stored within an object or physical system due to its position, physical shape, or chemical composition.

Kinetic Energy ($\text{KE}$)

The form of energy an object possesses as a result of its motion, given mathematically by $\frac{1}{2} m v^2$.

Joule ($\text{J}$)

The standard International System (SI) unit used to quantify energy and work ($1\,\text{kJ} = 1000\,\text{J}$).

Energy Transfer

The relocation of energy from one object, place, or system to another while maintaining the identical form of energy.

Energy Transformation

The process of converting energy from one distinct form into another (e.g., chemical energy turning into thermal and light energy).

Open System

A physical system capable of freely exchanging both energy and matter with its external surroundings.

Closed System

A physical system that can exchange energy with its surroundings, but cannot exchange matter.

Law of Conservation of Energy

A fundamental law of physics stating that energy cannot be created or destroyed, only transferred or transformed, maintaining a constant total quantity.

Lithosphere

The rigid, brittle outer shell of Earth consisting of the crust and the uppermost portion of the mantle, fragmented into moving tectonic plates.

Divergent Boundary

A constructive tectonic plate boundary where plates separate, permitting rising mantle magma to cool and solidify into new crust (e.g., Iceland along the Mid-Atlantic Ridge).

Convergent Boundary

A destructive tectonic plate boundary where plates move toward each other, resulting in subduction and crust destruction or the formation of collision fold mountains (e.g., the Himalayas).

Transform Boundary

A conservative tectonic boundary where adjacent plates grind horizontally past one another, generating fault lines and earthquakes without creating or destroying crust (e.g., the San Andreas Fault).

Continental Drift

Alfred Wegener's 1912 hypothesis proposing that Earth's continents were once assembled into a single supercontinent (Pangaea) before splitting apart and drifting across the globe.

Sea Floor Spreading

Harry Hess's geological theory proposing that new oceanic crust continually generates at mid-ocean ridges and spreads laterally away before subducting at oceanic trenches.

Earthquake

The abrupt, intense shaking of Earth's surface resulting from the sudden release of built-up mechanical stress along a fault line.

Volcano

A rupture or opening in Earth's crust that permits molten rock (magma), ash, and volcanic gases to erupt onto the surface.

Mineral

A naturally occurring, inorganic solid exhibiting a definite chemical composition and an ordered, repeating internal crystal structure.

Rock

A naturally occurring solid aggregate composed of one or more minerals or mineraloids bound together.

Igneous Rock

Rock created by the cooling, crystallization, and solidification of molten rock (magma beneath the surface or lava upon the surface).

Intrusive Igneous Rock

Igneous rock formed from magma cooling slowly deep below Earth's surface, resulting in large, visible interlocking crystals (e.g., granite).

Extrusive Igneous Rock

Igneous rock formed from lava cooling rapidly on Earth's exterior, forming microscopic crystals or a glassy, vesicular texture (e.g., basalt, pumice, obsidian).

Sedimentary Rock

Rock formed by the weathering, erosion, deposition, compaction, and cementation of mineral particles, rock fragments, or organic remains over time.

Clastic Sedimentary Rock

Sedimentary rock produced from mechanical weathering debris and compacted fragments (clasts) of pre-existing rocks (e.g., conglomerate, sandstone, shale).

Metamorphic Rock

Rock formed when an existing parent rock undergoes profound physical or chemical restructuring caused by extreme heat and pressure without complete melting.

Regional Metamorphism

Large-scale metamorphism occurring over broad continental zones under directed pressure and high temperatures, commonly yielding foliated, banded rocks.

Contact Metamorphism

Localised thermal metamorphism occurring when country rock directly abuts a hot magma intrusion, altering rocks primarily via intense heat to form non-foliated textures (e.g., limestone into marble).

Rock Cycle

A dynamic, continuous geological sequence of processes through which igneous, sedimentary, and metamorphic rocks are formed, altered, destroyed, and reformed over geological timescales.

Fossil

The preserved remains, impressions, or traces of past living organisms embedded within rock strata, almost exclusively found in sedimentary rock.

Law of Superposition

A geological principle establishing that within undisturbed sedimentary rock layers, the oldest stratum lies at the bottom, with progressively younger layers situated on top.

Rube Goldberg Machine

A deliberately over-engineered contraption designed to execute an elementary task through an intricate, sequential series of energy transfers and transformations.