OCR • J248 • 39 key terms
Activation energy
The minimum amount of energy required to break the initial bonds in reactants and start a chemical reaction.
From: Physical vs Chemical Changes
Allotrope
Different structural forms of the same element existing in the same physical state.
From: Structural Representations
Ball and stick model
A 3D physical or visual representation where spheres represent atoms and rods represent chemical bonds.
From: Structural Representations
Boiling Point
The specific temperature at which a liquid turns into a gas throughout the bulk of the substance.
From: Features of the Particle Model
Buckminsterfullerene
A hollow spherical fullerene molecule with the formula , consisting of exactly 20 hexagons and 12 pentagons.
From: Structural Representations
Chemical Change
A change that involves the breaking and making of chemical bonds to form new substances with different properties.
From: Features of the Particle Model
Combustion
A chemical reaction in which a substance reacts rapidly with oxygen, often producing heat and light (burning).
From: Physical vs Chemical Changes
Compressibility
The ability of a substance to be squashed into a smaller volume, which is high in gases due to large spaces between particles.
From: Features of the Particle Model
Condensation
The change of state from a gas to a liquid as a substance cools and particles are pulled together by attractive forces.
From: Features of the Particle Model
Conservation of Mass
The principle that mass is conserved during any state change because the total number of particles remains exactly the same.
From: Features of the Particle Model
Delocalised electron
An electron that is not associated with a single atom or covalent bond, making it free to move throughout a structure.
From: Structural Representations
Density
The mass per unit volume of a substance, which generally decreases from a solid to a gas as the same mass occupies a larger volume.
From: Features of the Particle Model
Diamond
A giant covalent structure of carbon where each atom is strongly covalently bonded to four others in a rigid 3D tetrahedral lattice.
From: Structural Representations
Displayed formula
A 2D representation showing every atom and every bond in a molecule as individual lines.
From: Structural Representations
Dot and cross diagram
A 2D representation showing the arrangement of electrons in atoms or ions, using dots for electrons from one atom and crosses for another.
From: Structural Representations
Electrostatic forces
The forces of attraction or repulsion between particles due to their electric charges, which are ignored in the simple particle model.
From: Limitations of the Particle Model
Endothermic
A process (like bond breaking) that takes in heat energy from the surroundings.
From: Physical vs Chemical Changes
Exothermic
A process (like bond making) that releases heat energy to the surroundings.
From: Physical vs Chemical Changes
Fluidity
The ability of particles to move past each other, allowing a substance like a liquid or gas to flow.
From: Features of the Particle Model
Fullerene
A molecule of carbon atoms with a hollow shape, typically consisting of interlocking hexagonal and pentagonal rings.
From: Structural Representations
Giant covalent structure
A 3D network of atoms held together by strong covalent bonds extending continuously throughout the lattice.
From: Structural Representations
Graphene
A single 2D sheet of graphite, consisting of a continuous hexagonal lattice of carbon atoms just one atom thick.
From: Structural Representations
Graphite
A giant covalent structure of carbon where each atom is bonded to three others, forming flat hexagonal layers held together by weak intermolecular forces.
From: Structural Representations
Inelastic spheres
A specific simplification where particles are treated as hard, non-deformable balls that do not change shape and have no internal subatomic structure.
From: Limitations of the Particle Model
Intermolecular forces
Weak forces of attraction between individual molecules that must be overcome during melting or boiling.
From: Limitations of the Particle Model
Internal Energy
The total sum of the kinetic energy (temperature-related) and potential energy (stored in forces/bonds) of particles in a substance.
From: Features of the Particle Model
Kinetic energy
The energy possessed by particles due to their motion, which increases when a substance is heated.
From: Limitations of the Particle Model
Latent Heat
The energy required for a substance to change state without a change in temperature.
From: Features of the Particle Model
Lattice
A regular, repeating 3D arrangement of particles (atoms, ions, or molecules) in a solid.
From: Physical vs Chemical Changes
Melting Point
The specific temperature at which a solid absorbs enough energy to overcome attractive forces and turn into a liquid.
From: Features of the Particle Model
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