Edexcel IAL Chemistry Unit 1

Atom

The smallest, electrically neutral particle of an element that can take part in a reaction.

Element

A substance which cannot be broken down into simpler substances by chemical means and contains only one type of atom.

Ion

An electrically charged atom or group of atoms that has gained or lost electrons.

Molecule

The smallest electrically neutral particle of an element or compound which can exist on its own.

Compound

A pure substance containing two or more different atoms chemically joined together.

Empirical Formula

The smallest whole number ratio of atoms of each element in a compound or molecule.

Molecular Formula

The actual number of atoms of each element in a compound or molecule.

Mole (mol)

The unit for amount of substance; contains 6.02 times 10²³ particles.

Avogadro Constant (L)

6.02 times 10²³ mol^-1.

Relative Atomic Mass (A_r)

The weighted average mass of an atom of an element relative to 1/12th the mass of a carbon-12 atom.

Molar Mass

The mass per mole of a substance (gmol^-1).

Molar Volume

The volume occupied by 1 mole of any gas at a specific temperature and pressure (24 dm³ at RTP).

Ideal Gas Equation

pV = nRT (where p is pressure in Pa, V is volume in m³, T is temp in K).

Concentration

The amount of solute (mol) dissolved in a volume of solution (dm³).

Atom Economy

(Molar mass of desired product / Sum of molar masses of all products) x 100.

Percentage Yield

(Actual yield / Theoretical yield) x 100.

Proton

Relative mass 1, relative charge +1, located in the nucleus.

Neutron

Relative mass 1, relative charge 0, located in the nucleus.

Electron

Relative mass 1/1840, relative charge -1, located in orbitals.

Atomic Number

The number of protons in the nucleus of an atom.

Mass Number

The total number of protons and neutrons in the nucleus.

Isotopes

Atoms of the same element with the same number of protons but different numbers of neutrons.

Mass Spectrometer Step 1

Vaporisation: The sample is turned into a gas.

Mass Spectrometer Step 2

Ionisation: Gaseous atoms are bombarded with high-energy electrons to form 1+ cations.

Mass Spectrometer Step 3

Acceleration: Cations are accelerated by an electric field to the same kinetic energy.

Mass Spectrometer Step 4

Velocity Selection: Ions are filtered by speed.

Mass Spectrometer Step 5

Deflection: Ions are deflected by a magnetic field according to their mass-to-charge (m/z) ratio.

Molecular Ion Peak

The peak with the highest m/z ratio, representing the relative molecular mass (M_r).

Quantum Shell

The main energy level of an electron (n=1, 2, 3, etc.).

Orbital

A region that can hold up to two electrons with opposite spins.

s-orbital Shape

Spherical.

p-orbital Shape

Dumbbell-shaped.

Hund's Rule

Electrons occupy orbitals of the same energy singly before pairing to minimize repulsion.

First Ionisation Energy

The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of 1+ gaseous ions.

Successive IE "Big Jump"

Indicates that an electron is being removed from a inner quantum shell closer to the nucleus.

Periodicity

The repeating pattern of physical and chemical properties across periods.

Ionic Bond

The strong net electrostatic force of attraction between oppositely charged ions.

Hydrocarbon

A compound containing only carbon and hydrogen.

Homologous Series

A family of compounds with the same functional group and general formula, differing by CH₂.

Functional Group

An atom or group of atoms that determines the chemical properties of a molecule.

Structural Isomerism

Molecules with the same molecular formula but different structural formulas.

Saturated

Contains only single carbon-carbon bonds (Alkanes).

Unsaturated

Contains at least one C=C double bond (Alkenes).

Free Radical

A species with an unpaired electron.

Homolytic Fission

The breaking of a covalent bond where each atom takes one electron from the pair.

Heterolytic Fission

The breaking of a covalent bond where one atom takes both electrons.

Electrophile

An electron-pair acceptor (attracted to high electron density).

Nucleophile

An electron-pair donor (attracted to electron-deficient areas).

Substitution Reaction

An atom or group is replaced by another.

Addition Reaction

Two molecules react to form a single larger molecule.

Hazard: Toxic

Represented by a skull and crossbones; can cause death if swallowed or inhaled.

Hazard: Corrosive

Can damage skin or eyes on contact and destroy metals.

Fractional Distillation

The process of separating crude oil into fractions based on boiling points.

Cracking

Breaking long-chain alkanes into smaller, more useful alkanes and alkenes.

Reforming

Converting straight-chain alkanes into branched or cyclic hydrocarbons for better combustion.

Cation

A positively charged ion (usually metal), smaller than its parent atom.

Anion

A negatively charged ion (usually non-metal), larger than its parent atom.

Isoelectronic Ions

Ions with the same number of electrons (e.g., N^3-, O^2-, F^-, Na⁺, Mg²⁺, Al³⁺.

Polarisation

The distortion of the electron density of an anion by a neighboring cation.

Polarising Power

The ability of a cation to distort an anion; increased by high charge and small radius.

Polarisability

The ease with which an anion's electron cloud is distorted; increased by large radius and high charge.

Covalent Bond

The strong electrostatic attraction between two nuclei and a shared pair of electrons.

Dative Covalent Bond

A bond where both electrons in the shared pair come from the same atom.

Bond Length

The distance between the nuclei of two covalently bonded atoms.

Bond Energy

The energy required to break one mole of a specific bond in the gaseous state.

Electronegativity

The ability of an atom to attract a bonding pair of electrons in a covalent bond.

Polar Bond

A covalent bond where electrons are shared unequally due to a difference in electronegativity.

Metallic Bonding

The strong electrostatic attraction between metal cations and a sea of delocalised electrons.

Giant Ionic Lattice

A regular 3D arrangement of oppositely charged ions (e.g., NaCl).

Giant Covalent Structure

A 3D network of atoms joined by covalent bonds (e.g., Diamond, Graphite, Silicon).

Linear Shape

2 bonding pairs, 0 lone pairs, 180° bond angle.

Trigonal Planar Shape

3 bonding pairs, 0 lone pairs, 120° bond angle.

Tetrahedral Shape

4 bonding pairs, 0 lone pairs, 109.5° bond angle.

Trigonal Pyramidal Shape

3 bonding pairs, 1 lone pair, 107° bond angle (e.g., NH₃.

V-Shaped / Bent

2 bonding pairs, 2 lone pairs, 104.5° bond angle (e.g., H₂O).

Mole (Mass)

Mass / Molar Mass

Mole (Gas at RTP)

Volume / 24

Ideal Gas Equation

pV = nRT

Pressure unit for pV=nRT

Pascals (Pa)

Volume unit for pV=nRT

Cubic meters (m3)

Temperature unit for pV=nRT

Kelvin (K)

Atom Economy

(Molar mass of desired product / Total molar mass of all products) x 100

Percentage Yield

(Actual yield / Theoretical yield) x 100

Parts per million (ppm)

(Mass of solute / Mass of solution) x 1,000,000

Density

Mass / Volume

Reactivity Series (High to Low)

K, Na, Li, Ca, Mg, Al, Zn, Fe, Cu, Ag, Au

Group 2 Reactivity Trend

Increases down the group

Group 7 Reactivity Trend

Decreases down the group

Electronegativity Trend

Increases across a period and up a group

First Ionisation Energy Trend

Increases across a period, decreases down a group

Atomic Radius Trend

Decreases across a period, increases down a group

Chlorine + Potassium Bromide

Orange solution forms (Bromine displaced)

Bromine + Potassium Iodide

Brown solution forms (Iodine displaced)

Complete Combustion

Carbon Dioxide + Water

Incomplete Combustion

Carbon Monoxide + Water

Alkane + Halogen (UV)

Halogenoalkane + Hydrogen Halide

Alkene + Hydrogen (Nickel)

Alkane

Alkene + Bromine Water

1,2-dibromoalkane (Colourless)

Alkene + Steam

Alcohol

Alkene + Acidified Potassium Manganate

Diol (Purple to Colorless)