Grade 8 Chemistry Complete Study Guide

Comprehensive vocabulary flashcards covering matter, atomic structure, the periodic table, physical/chemical changes, acids/bases, metals, and plastics based on Grade 8 Chemistry notes.

Matter

Defined as anything that has mass (contains a specific quantity of particles) and occupies volume (takes up physical space).

Diffusion

The process by which scent molecules or airborne waste gasses move from an area of high concentration and mix with air particles to spread throughout a space.

Solid

A state of matter with a fixed shape and volume, characterized by a regular, repeating lattice of tightly packed particles with extremely strong intermolecular forces and low kinetic energy.

Liquid

A state of matter with a fixed volume but variable shape, characterized by particles that are close together in a random arrangement and can slide past each other.

Gas

A state of matter with variable volume and shape, characterized by highly dispersed particles in rapid, random, straight-line motion with negligible attractive forces.

Sublimation

The process where a solid (such as dark purple iodine crystals) converts directly into a gas without passing through a liquid phase.

Deposition

The process where a gas undergoes a phase change back into solid crystals upon contacting a cold surface.

Physical Change

A combination or process resulting in a change of state or appearance of the same substance where no new chemical compounds are formed, and is generally easily reversible.

Chemical Change

A combination or process resulting in the formation of entirely new chemical substances driven by the breaking and making of chemical bonds; typically permanent and difficult to reverse.

Atomic Number ($Z$)

The total number of protons in the nucleus of an atom, which defines the identity of the element.

Mass Number ($A$)

The total number of protons plus neutrons inside the nucleus of an atom.

Proton ($p^+$)

A subatomic particle located in the nucleus with a relative mass of $1$ and a relative charge of $+1$.

Neutron ($n^0$)

A subatomic particle located in the nucleus with a relative mass of $1$ and a relative charge of $0$.

Electron ($e^-$)

A subatomic particle orbiting in shells/energy levels with a relative mass of $1/1840$ and a relative charge of $-1$.

Element

A pure substance made entirely from one type of atom which cannot be broken down into simpler substances by chemical means.

Compound

A fixed chemical combination of two or more different types of atoms or elements bonded together.

Mixture

A physical combination of different elements or compounds that are not chemically bonded together and can be separated by physical techniques.

Homogeneous Mixture

A mixture that has a uniform composition and appearance throughout, such as a salt solution or air.

Heterogeneous Mixture

A mixture with a non-uniform composition where individual components remain distinct, such as sand in water or oil and vinegar.

Tyndall Effect

The scattering of light beams by a colloid, which is a stable mixture with particles of intermediate size ($1$ to $1000\,nm$).

Acid

A substance with a pH value less than $7$ ($pH < 7$), which tastes sour, releases hydrogen ions ($H^+$) in solution, and turns blue litmus paper red.

Base

A substance with a pH value greater than $7$ ($pH > 7$), which tastes bitter, feels slippery, releases hydroxide ions ($OH^-$) in solution, and turns red litmus paper blue.

Alkali

A water-soluble base.

Neutralization

The chemical reaction between an acid and a base to produce a neutral ionic compound (salt) and water ($Acid + Base \rightarrow Salt + Water$).

Metal

Elements typically possessing $1$ to $3$ electrons in their outermost shell that readily lose these electrons to form positive ions; they are shiny, malleable, ductile, and excellent conductors.

Non-Metal

Elements typically possessing $4$ to $8$ electrons in their valence shell that tend to gain or share electrons; they are often dull, brittle as solids, and poor conductors.

Corrosion (Rusting)

An electrochemical process that strictly requires the simultaneous presence of Oxygen ($O_2$) and Water ($H_2O$).

Alloy

A solid solution or mixture of two or more metals (or a metal and a non-metal) combined to create a material with enhanced physical properties.

Stainless Steel

An alloy of Iron + Carbon + Chromium + Nickel that is extremely strong and entirely rust-resistant, used for cutlery and surgical tools.

Thermoplastics

Synthetic non-metals that soften and melt completely upon heating, allowing them to be repeatedly reshaped and recycled.

Thermosetting Plastics

Plastics that undergo chemical cross-linking during their initial curing and become permanently rigid, meaning they cannot be remelted or reshaped upon heating.