General Chemistry – Key Vocabulary

Essential vocabulary covering atomic structure, bonding, acids–bases, redox, polymers, biochemistry, analytical methods and green chemistry for exam review.

Atom

Smallest unit of an element, composed of a nucleus and surrounding electrons.

Proton

Positively charged particle in the nucleus; defines the atomic number.

Neutron

Neutral nuclear particle that contributes to atomic mass.

Electron

Negatively charged particle moving in shells around the nucleus.

Atomic Number

Number of protons in an atom; determines its place in the periodic table.

Mass Number

Total number of protons plus neutrons in one atom.

Isotope

Atoms of the same element with different mass numbers.

Relative Atomic Mass (Ar)

Average mass of natural isotopes on a scale where 12C = 12.00.

Electron Shell

Energy level around the nucleus holding a fixed maximum number of electrons.

Valence Electrons

Electrons in the outermost shell; involved in chemical bonding.

Octet Rule

Atoms gain, lose or share electrons to obtain eight valence electrons.

Period (Periodic Table)

Horizontal row; number equals shells in use.

Group (Periodic Table)

Vertical column; elements share valence electron patterns.

Metal

Element that forms cations, conducts heat/electricity and shows metallic bonding.

Non-metal

Element that forms anions or covalent bonds; right-hand side of table.

Halogen

Reactive group-17 non-metal (F, Cl, Br, I, At).

Noble Gas

Group-18 element with complete outer shell; chemically inert.

Cation

Positively charged ion formed by electron loss.

Anion

Negatively charged ion formed by electron gain.

Ion Bond (Ionic Bond)

Electrostatic attraction between oppositely charged ions in a lattice.

Covalent Bond

Shared pair of electrons between two non-metal atoms.

Metallic Bond

Attraction between positive metal ions and a sea of delocalised electrons.

Molecule

Neutral group of atoms held together by covalent bonds.

Molecular Mass

Sum of atomic masses in a molecule, expressed in u.

Polar Bond

Covalent bond with unequal electron sharing, creating δ+ and δ– ends.

Dipole-Dipole Force

Attraction between permanent molecular dipoles.

Van der Waals Force

Weak attraction from temporary dipoles in all molecules.

Hydrogen Bond

Strong dipole interaction involving H bonded to N, O, or F.

Lewis Structure

Diagram showing bonds and lone pairs in a molecule.

VSEPR Theory

Predicts 3-D shape by maximizing separation of electron pairs.

Tetrahedral

Molecular geometry with four regions of electron density; 109.5° angles.

Ionic Compound (Salt)

Substance of cations and anions in a regular ion lattice.

Electronegativity

Ability of an atom to attract bonding electrons; influences bond polarity.

Acid

Proton donor that increases [H3O+] in water.

Base

Proton acceptor producing OH⁻ or removing H⁺ from water.

pH

–log[H3O+]; numerical measure of acidity/basicity.

Water Constant (Kw)

[H3O+][OH⁻] = 1.0 × 10⁻¹⁴ at 25 °C.

Buffer Solution

Mixture of weak acid and its base resisting pH changes.

Redox Reaction

Reaction with simultaneous oxidation and reduction (electron transfer).

Oxidation

Loss of electrons or increase in oxidation number.

Reduction

Gain of electrons or decrease in oxidation number.

Oxidator (Oxidizing Agent)

Species that accepts electrons and is reduced.

Reductor (Reducing Agent)

Species that donates electrons and is oxidized.

Half-Reaction

Equation showing electron loss or gain separately in redox processes.

Electrochemical Cell

Device converting chemical redox energy to electrical energy or vice versa.

Anode (Voltaic)

Electrode where oxidation occurs; negative in galvanic cells.

Cathode (Voltaic)

Electrode where reduction occurs; positive in galvanic cells.

Electrolyte

Conducting solution containing ions that complete the circuit.

Polymer

Very large molecule made of repeating monomer units.

Monomer

Small molecule that can join to form a polymer.

Addition Polymerisation

Process where unsaturated monomers add to form a polymer without by-product.

Condensation Polymerisation

Polymer formation with elimination of small molecules like water.

Isomer

Compounds with same molecular formula but different structures.

Structural Isomer

Isomers differing in atom connectivity or functional-group position.

Cis-Trans Isomer

Stereoisomers with restricted rotation showing groups on same/opposite sides.

Enantiomer

Pair of molecules that are non-superimposable mirror images.

Hydrolysis

Reaction where water splits a molecule into two fragments.

Esterification

Condensation of an alcohol with a carboxylic acid forming an ester and water.

Amide

Compound containing –CONH– group; product of acid plus amine.

Amino Acid

Molecule with both –NH2 and –COOH groups; building block of proteins.

Peptide Bond

Amide linkage between amino acid residues in proteins.

Enzyme

Protein catalyst with high specificity and activity under mild conditions.

DNA

Double-helical nucleic acid storing genetic information in base sequences.

RNA

Single-strand nucleic acid involved in gene expression and protein synthesis.

Chromatography

Separation technique based on differential distribution between mobile and stationary phases.

Gas Chromatography (GC)

Chromatography with gas mobile phase; retention time identifies components.

Mass Spectrometry

Technique that ionises molecules and measures mass-to-charge ratios for structural analysis.

Titration

Volumetric analysis method using a standard solution to determine unknown concentration.

Indicator

Substance showing a visible change at titration end point.

Atom Economy

% of reactant atoms incorporated into desired product; measure of synthetic efficiency.

E-Factor

Mass of waste per mass of product; lower values mean greener process.

Green Chemistry

Design of chemical processes that reduce or eliminate hazardous substances.

Cracking

Thermal or catalytic splitting of large hydrocarbons into smaller ones.

Polymerisation Degree

Average number of monomer units in a polymer chain.

Triglyceride

Triester of glycerol with three long-chain fatty acids (fat/oil).

Phospholipid

Glycerol ester with two fatty acids and a phosphate; major membrane component.

Monosaccharide

Single-ring carbohydrate such as glucose or fructose.

Polysaccharide

Carbohydrate polymer like starch, glycogen, or cellulose.

Photosynthesis

Light-driven conversion of CO2 and H2O into glucose and O2 in plants.

Fossil Fuel

Energy source formed from ancient biomass: coal, oil, natural gas.

Buffer Capacity

Amount of acid/base a buffer can neutralise without significant pH change.

Kw (Water Constant)

Product of [H+][OH-]; 1.0 × 10⁻¹⁴ at 25 °C.

Kwik Hydraterion?

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Catalyst

Substance that speeds a reaction without being consumed.