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A–Z
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Chemical Bonding & Molecular Structure

Polar Covalent Bond

A covalent bond in which the shared electrons are unequally distributed because the bonded atoms differ in electronegativity.

δ⁺A—Bδ⁻ D
Chemical Bonding & Molecular Structure

Polarisability

The ease with which the electron cloud of an atom, ion or molecule can be distorted by an external electric field.

μ_induced = α × E C·m²/V
Chemical Bonding & Molecular Structure

Polarising Power

The ability of a cation to distort the electron cloud of a neighbouring anion.

∝ charge / radius² Dimensionless
Foundations of Chemistry

Polyatomic Ion

A covalently bonded group of atoms that carries an overall electrical charge and behaves as a single unit in reactions.

C (charge)
Inorganic & Coordination Chemistry

Polydentate Ligand

A ligand that binds to a single metal centre through three or more donor atoms.

Dimensionless
Biochemistry & Polymer Chemistry

Polymer

A large molecule built from many repeating structural units joined by covalent bonds.

–(A)ₙ– g/mol
States of Matter & Gas Laws

Polymorphism

The ability of a single substance to exist in more than one crystalline form.

Dimensionless
Acids, Bases & Salts

Polyprotic Acid

An acid capable of donating more than one proton per molecule.

H₂A ⇌ H⁺ + HA⁻ ⇌ 2H⁺ + A²⁻ mol/L
Biochemistry & Polymer Chemistry

Polysaccharide

A carbohydrate polymer built from many monosaccharide units linked by glycosidic bonds.

(C₆H₁₀O₅)ₙ Dimensionless
Organic Chemistry

Position Isomerism

Structural isomerism arising from a functional group occupying different positions on the same carbon skeleton.

Dimensionless
Solutions & Colligative Properties

Positive Deviation

Behaviour in which a solution exerts a higher vapour pressure than Raoult's law predicts.

p > x p° Pa
Nuclear & Radiochemistry

Positron Emission

Radioactive decay in which a proton converts into a neutron, emitting a positron and a neutrino.

p → n + e⁺ + ν MeV
Chemical Kinetics & Catalysis

Pre-exponential Factor

The constant A in the Arrhenius equation, representing the frequency of appropriately oriented collisions.

A = pZ Various
Stoichiometry & Chemical Reactions

Precipitate

An insoluble solid that separates from a solution as the result of a chemical reaction.

g
Stoichiometry & Chemical Reactions

Precipitation Reaction

A reaction in which two solutions combine to form an insoluble solid that separates from the mixture.

A⁺(aq) + B⁻(aq) → AB(s) Dimensionless
Analytical Chemistry & Spectroscopy

Precipitation Titration

A titration in which the analyte and titrant combine to form an insoluble product.

Ag⁺ + Cl⁻ → AgCl(s) mol/L
Foundations of Chemistry

Precision

The closeness of repeated measurements of the same quantity to one another, regardless of their accuracy.

RSD = (s / x̄) × 100 Dimensionless
Chemical Equilibrium

Predicting Precipitation

The use of the ionic product and solubility product to decide whether a solid will form on mixing two solutions.

Q_sp > Ksp → precipitate Dimensionless
Chemical Equilibrium

Pressure Equilibrium Constant

The equilibrium constant for a gaseous reaction expressed in terms of partial pressures.

Kp = p_C^c p_D^d / p_A^a p_B^b Various
Electrochemistry & Redox

Primary Cell

A cell in which the electrode reaction is irreversible, so it cannot be recharged.

V
Analytical Chemistry & Spectroscopy

Primary Standard

A highly pure, stable substance that can be weighed accurately and used directly to prepare a solution of known concentration.

g/mol
Biochemistry & Polymer Chemistry

Primary Structure

The linear sequence of amino acids in a polypeptide chain.

Dimensionless
Inorganic & Coordination Chemistry

Primary Valence

In Werner's theory, the ionisable valence of a metal, equal to its oxidation state and satisfied by negative ions.

Dimensionless
Atomic Structure & Periodicity

Principal Quantum Number

The quantum number n that specifies the main energy level and average distance of an electron from the nucleus.

E_n = −13.6 Z² / n² eV Dimensionless