AICE Chemistry AS Ultimate Exam Study Guide (Cambridge 9701)

A comprehensive vocabulary review of key terms, definitions, and concepts from the AICE Chemistry AS 9701 syllabus, covering physical, inorganic, and organic chemistry topics.

Isotopes

Atoms of the same element with the same proton number but different numbers of neutrons, resulting in the same chemical properties but different physical properties like density and rate of diffusion.

Relative atomic mass ($A_r$)

The weighted mean mass of an atom of an element compared to $\frac{1}{12}$ of the mass of a $^{12}C$ atom.

Mole

The amount of substance containing $6.02 \times 10^{23}$ particles, which is known as Avogadro's number.

First Ionisation Energy (IE)

The energy needed to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous $+1$ ions ($X(g) \rightarrow X^+(g) + e^-$).

Hund's rule

The rule stating that electrons occupy $p$ or $d$ orbitals singly with parallel spins before pairing.

Pauli exclusion principle

The principle stating that each orbital holds a maximum of two electrons with opposite spin.

Dative (coordinate) bond

A covalent bond where both shared electrons come from one atom, such as in $NH_4^+$ or $Al_2Cl_6$.

Electronegativity

The ability of an atom to attract bonding electrons, which increases across periods and decreases down groups.

Hydrogen bonding

The strongest intermolecular force, occurring when $H$ is bonded to the highly electronegative atoms $N$, $O$, or $F$.

Enthalpy change ($\Delta H$)

The heat energy change measured at constant pressure, expressed in $kJ\,mol^{-1}$.

Standard enthalpy of formation ($\Delta H_f^\theta$)

The enthalpy change when 1 mole of a compound forms from its elements in their standard states.

Hess's Law

The principle that the total enthalpy change for a reaction is independent of the route taken.

Bond enthalpy

The energy required to break 1 mole of a bond in gaseous molecules, often expressed as average values for polyatomic molecules.

Oxidation

The loss of electrons or a decrease in oxidation number.

Disproportionation

A redox reaction where the same element is simultaneously oxidised and reduced.

Dynamic equilibrium

A state in a reversible reaction in a closed system where the forward and reverse rates are equal and macroscopic properties remain constant.

Le Chatelier's Principle

If a system at equilibrium is disturbed, the system shifts its position to counteract the change.

Brønsted–Lowry Acid

A species that acts as a proton ($H^+$) donor.

Activation energy ($E_a$)

The minimum energy particles must possess during a collision for a reaction to occur.

Boltzmann distribution

A graph showing the number of molecules versus kinetic energy, demonstrating how the proportion of molecules with energy $\geq E_a$ changes with temperature or catalysts.

Amphoteric oxide

An oxide that can react with both acids and alkalis, such as $Al_2O_3$.

Polarising power

The ability of a cation to distort the electron cloud of an anion, which is proportional to the cation's charge/radius ratio.

Stereoisomers

Molecules with the same structural formula but a different spatial arrangement of atoms, including cis-trans ($E/Z$) and optical isomers.

Chiral centre

A carbon atom bonded to four different groups, resulting in non-superimposable mirror images called enantiomers.

Homolytic fission

Bond breaking where each atom from the bond receives one electron, resulting in the formation of free radicals.

Electrophile

An electron-pair acceptor, typically a positive or electron-deficient species like $Br^+$ or $H^+$.

Nucleophile

An electron-pair donor, such as a lone pair or negative ion like $OH^-$ or $CN^-$.

Markovnikov's rule

In the electrophilic addition of $HX$ to an alkene, the $H$ adds to the carbon atom that already has more $H$ atoms attached.

Brady's reagent (2,4-DNPH)

A reagent used to detect the carbonyl group ($C=O$) in aldehydes and ketones, forming an orange/yellow crystalline precipitate.

Tollens' reagent

A solution of $Ag(NH_3)_2^+$ used to distinguish aldehydes (which form a silver mirror) from ketones.

Molecular ion peak ($M^+$)

The peak in a mass spectrum with the highest $m/z$ value (ignoring the $M+1$ peak), represents the relative molecular mass ($M_r$) of the compound.

Concordant titres

Titration results that are within $\pm 0.10\,cm^3$ of each other, used to calculate the mean titre.