Grade 8 Physical Sciences: Elements, Compounds, and the Particle Model of Matter

Flashcards covering definitions and terminology for Grade 8 Chemistry, including categories of matter, subatomic particles, states of matter, and separation techniques.

Pure substance

A material that is made of only one type of particle, which may be atoms, molecules, or ions.

Compound

A chemical substance made of only one type of particle consisting of two or more different elements chemically joined together in a fixed ratio.

Electrolysis

A chemical reaction caused by electrical charges used to break up a pure salt into the elements from which it is made.

Element

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

Molecule

A particle that is made from more than one atom joined chemically to another.

Diatomic

A word used to describe a molecule made of two atoms joined together chemically.

Atom

The basic particle or 'building block' of matter that shows the chemical properties of an element and cannot be broken down further using chemical means.

Ion

An atom that has an unbalanced charge and is not electrically neutral, existing as either a cation or an anion.

Anion

An ion that carries a negative charge, such as a chlorine ion ($Cℓ^-$).

Cation

An ion that carries a positive charge, such as a copper ion ($Cu^{++}$) or sodium ion ($Na^+$).

Electrode

A conductor, often a carbon graphite rod, through which electricity enters or leaves a substance.

Anode

A positively charged electrode that attracts negative anions in a solution towards it.

Cathode

A negatively charged electrode that attracts positive cations in a solution towards it.

Electrolyte

A salt solution containing positive and negative ions that conducts electricity through it.

Cell

A single device that is used to generate electricity.

Battery

A power source consisting of a collection of cells joined to each other.

Periodic Table of Elements

A classification system devised by Dmitri Mendeleev in the 1860s that organises elements into groups sharing similar physical and chemical properties.

Chemical bond

The force that holds atoms together in the particles of a compound.

Mixture

A combination of different substances in which the component parts are individually distinct and are not chemically combined.

Homogeneous mixture

A mixture where the substances are in the same phase and are equally spread, such as orange syrup and water.

Heterogeneous mixture

A mixture where the substances are of different phases and are unequally spread, such as fruit salad or cereal.

Solute

A solid substance that mixes completely with a liquid to form a pure homogenous mixture.

Solvent

A liquid substance, such as water, that mixes completely with a solid to form a solution.

Solution

A pure homogenous mixture made from a solute mixed with a solvent.

Scientific Theory

A well-established explanation of scientific data that is repeatedly tested but typically cannot be proven.

Model

A construction of reality that explains the structure and functioning of objects and processes.

Kinetic energy

The energy that an object possesses due to its motion; also referred to as movement energy.

Brownian motion

The continuous, random, irregular movement of particles caused by collisions with other particles.

Diffusion

The movement of atoms or molecules from an area of higher concentration to an area of lower concentration until they are uniformly spread out.

Temperature

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

Melting

The process of making a liquid from a solid through heating.

Evaporation

The process of a liquid changing into a gas through heating.

Condensation

The process of the conversion of a gas into a liquid through cooling.

Solidification

The process of making a liquid a solid through cooling or freezing.

Sublimation

A process of a solid changing directly into a gas through heating, such as with solid carbon dioxide or iodine crystals.

Plasma

The fourth state of matter, consisting of an ionized gas with positive ions and free electrons at very high temperatures.

Density

The relationship between the mass and volume of an object, calculated as $D = \frac{m}{V}$.

Expansion

The process by which a material increases in volume due to the addition of heat.

Contraction

The process by which a material decreases in volume due to the removal of heat.

Sieving

The separation of particles from a mixture based on the difference in particle size using sieve plates.

Chromatography

A technique used to identify chemicals in foods or inks where a solvent separates different sized chemicals based on their speed.

Distillation

A separation method based on different boiling points where a liquid is separated from a solution and collected by condensation.

Proton

A subatomic particle found in the nucleus that carries a positive charge.

Neutron

A subatomic particle found in the nucleus that is neutral and has no charge.

Electron

A subatomic particle found in the space around the nucleus (orbital) that carries a negative charge.

Nucleons

The collective name for protons and neutrons which give the atom its mass.